any chevy mechanics here?

[labradigger1]

My 03 chevy silverado 1500 w/ 4.3l v6 started something new yesterday, was driving along and engine started running terrible, check engine light flashing.
Today i scanned for codes and p0300 (multiple engine misfire).
I pulled the distributer shaft to check the cam gear, looks good.
I replaced the entire distributer assy last year.
Installed new cap and rotor button.
changed plug wires.
installed new ignition coil,
changed fuel and air filter.
checked all 6 spark plugs, changed these less than 1 year ago w/ double platinum plugs, 5 of 6 looked textbook light tan, #2 cylinder plug was black and slightly sooty indicating rich mixture or incomplete combustion, #2 was NOT oily. Changed wires after inspecting plugs. All electrodes and porcelin looked good.
Looked for vacuum leaks and leaking/cracked intake, no signs of leaks. Visually looked, listened w/stethescope and screwdriver, sprayed w/ ether. All looks ok.
Checked all wire connections.
Removed and inspected all 4 o2 sensors,
checked for exhaust restrictions, none found.

Engine idles terrible, runs terrible through all rpms, starts fair. Hot or cold temp does not seem to change things.
also, t-stat was bad and stuck open, changed it today also.
nothing i have done has helped. I have replaced the maf sensor before and it pulled a code. Only code is p0300 multiole missfire detected.
engine and truck has 177k miles. I never performed a compression check as plugs were not oily and engine does not consume oil.
I have not checked camshaft as trouble seems electrical to me.
i am at my witts end to possible causes. Any thoughts? I am a fair mechanic and would like to perform all work myself. Thanks, Lab

[Frosty Boolit]

Well I know that the 4.3 runs like hell when it is not running on all 6. Maybe you have a ignition coil pack gone bad. sometimes there are 3 sections that each do 2 cylinders. My bet is a spark issue since it still runs.

[merlin101]

Well I know that the 4.3 runs like hell when it is not running on all 6. Maybe you have a ignition coil pack gone bad. sometimes there are 3 sections that each do 2 cylinders. My bet is a spark issue since it still runs.

Thats a good idea to check, also I think those thing have a knock sensor mounted on the side of the block and remember something about when it goes bad it throws the timing WAY off. just another thing to check.

[Bullshop Junior]

Sounds like it could be a stuck valve. My 5.3 (2001) has seperate coil packs for each cylinder so that is a very good possibility. These trucks also have to have the air system tight..no leaks. My buddy had one that ran terrible for a long time and i finally figured it was just from the air filter not being in correctly. They are super picky. It could aslo be one of the ignition relays or one of the coil pack fuses. Did you check to see if it was sparking on #5?

[HeavyMetal]

How about O rings on the injectors?

Get some of that spray on white lythium grease and spray each injector base area while idling, if it gets better replace the O rings with the new blue ones from a chevy dealer.

If not go for the coil paks.

[labradigger1]

Thanks for the replies guys, mine only has one ignition coil instead of one for each cylinder, i installed a new coil yesterday to no avail. All plugs are firing a nice blue spark.

[Bullshop Junior]

Hmmmmm. Then i would say stuck valve, or a injector. Pull the valve cover off and see what its doing in there.

[labradigger1]

Hmmmmm. Then i would say stuck valve, or a injector. Pull the valve cover off and see what its doing in there.

I have been procrastonating pulling the valve covers but have been thinking stuck valve or worn cam lobes. If injector was at fault i would think excessive lean or rich condition would show up on plugs. I will check the valves and cam next week as i leave for deer camp tomorrow. Shure wish my ole truck was running ok to pull the camper. Camp is about 150 miles away from home. I will use the wifes x-terra instead. Thx, lab

[Bullshop Junior]

Worn cam lobe is a good possibilty. These newer "throwaway" engines chevy makes have problems with that and that had slipped my mind. I put aftermarket 3/4 cams in my truck about a week after i got it since it was acting up a little. It only had 92,000 on it at the time.

[CastingFool]

IMO, I don't think the 4.3 L engine is all that good and underpowered. Had one on a 90 GMC. Had problems with it, when the engine was torn down, one cylinder was found to be leaking real bad. At any rate, the engine was rebuilt, heads redone, and although it was much better, it never ran as well as it did before it had the problem. I used to get 21mph with it. I eventually replaced that truck with a 96 Silverado with a 350cu in 225hp engine. I was kinda leery of the expected gas mileage, but surprisingly, I got 19mph, and I had all the power I needed and more. The 96 had 80K miles when I first purchased. Today, it has 279K miles on it, and still running strong. My gas mileage has dropped to around 17 mph, but I don't drive it every day like I used to do.

[jonas302]

Quit wasting time and money on it and bring it to a shop your code reader does nothing for diagnosis my scanner will show what cylinders are causing the miss and mechanical causes are the least likely Have you cleaned the MAf sensor?

You would not believe the money people will spend to avoid taking it to the mechanic then when they finally bring it in for repair or scrap(: its an easy affordable fix

[6bg6ga]

Did you check the EGR valve? If it isn't seating correctly you get a rough idle.

[Bullshop Junior]

Quit wasting time and money on it and bring it to a shop your code reader does nothing for diagnosis my scanner will show what cylinders are causing the miss and mechanical causes are the least likely Have you cleaned the MAf sensor?

You would not believe the money people will spend to avoid taking it to the mechanic then when they finally bring it in for repair or scrap(: its an easy affordable fix

Alot of people also cant afford to pay $175 a hour to have someone mess their car up even worse. I have never had a car come back from a shop fixed, and will never take a car to a shop again. The last time i took one in to the dealer, it was for a fuel pump. $1100 later go to pick it up and it wont start. The warranty paid me back, i swapped it myself and will never take a vehichle to a shop or dealer again.

[6bg6ga]

Quit wasting time and money on it and bring it to a shop your code reader does nothing for diagnosis my scanner will show what cylinders are causing the miss and mechanical causes are the least likely Have you cleaned the MAf sensor?

You would not believe the money people will spend to avoid taking it to the mechanic then when they finally bring it in for repair or scrap(: its an easy affordable fix

This is so true. The time has long passed when you can drive the car or truck under the apple tree and work on it yourself. With the complexity of the newer systems it takes a factory scanner costing 10 grand and up to accurately diagnose the problem. Simply throwing parts at it is totally stupid.

So far you have spent how much money? It still isn't running correctly yet is it? And your not done yet.

[Bullshop Junior]

This is so true. The time has long passed when you can drive the car or truck under the apple tree and work on it yourself. With the complexity of the newer systems it takes a factory scanner costing 10 grand and up to accurately diagnose the problem. Simply throwing parts at it is totally stupid.

So far you have spent how much money? It still isn't running correctly yet is it? And your not done yet.

They actually make some decent scanners that are affordable. Mine hooks up to my laptop and it runs codes and diagnosics online. I rarely use it though. So far all my problems have been mechanical, and if i have a sensor throw a code i usually figure out a way to bypass it.

[6bg6ga]

They actually make some decent scanners that are affordable. Mine hooks up to my laptop and it runs codes and diagnosics online. I rarely use it though. So far all my problems have been mechanical, and if i have a sensor throw a code i usually figure out a way to bypass it.


While this type of scanner is better than the auto zone type of cheap **** out there its still not the quality of the Factory GM scanners.

I've been there before.

[Bullshop Junior]

No, its not. But in my case its better the taking it to a shop. Some of the shops in Fairbanks may be decent, thats over 100 miles away, and the two local shoos are run by druggies and i wouldnt take my car there if it beoke down right in front of the shop.

[6bg6ga]

Trust me...they are junk. Have had a number of hours on the GM scanner and the same on the laptop junk out there. The GM scanner is capable of 100% accuracy when diagnosing a problem and the laptop while close is no cigar. You simply cannot expect a cheap program to run head to head with the factory GM scanner and they don't.

I have laptop software for my Camaro and while its close its not 100%. Like I have said I have spent 100's of hours with both hooked up to my Z-28 and the laptop doesn't cut it.

[6bg6ga]

The laptop software is fine for programing the fuel tables and spark tables but when it comes to diagnostic codes its junk.

[Bullshop Junior]

I agree its not as good as the factory GM scanner. Butvi dont have ten grand to buy one of those, nor do i have the ability to tow my truck 120 miles to a decent shop, so the laptop gets by.

[labradigger1]

I concurr the aftermarket scanners are not par w/ dealer scanners.
i have the best scanner actron makes and it will also identify each cylinder individually, however, multiple missfire is what it is doing.
I have cleaned the maf sensor as suggested above.

[Bullshop Junior]

I concurr the aftermarket scanners are not par w/ dealer scanners.
i have the best scanner actron makes and it will also identify each cylinder individually, however, multiple missfire is what it is doing.
I have cleaned the maf sensor as suggested above.

Then i would be looking into the cam and valves next as bad as i hate to say it. Seems like you have checked pretty much everything else...

[6bg6ga]

I concurr the aftermarket scanners are not par w/ dealer scanners.
i have the best scanner actron makes and it will also identify each cylinder individually, however, multiple missfire is what it is doing.
I have cleaned the maf sensor as suggested above.


Did you check the EGR? May not show up in a scan

[6bg6ga]

An EGR that isn't seating will ALSO mirror a misfire condition. Are you showing a miss fire per a particular cylinder?

[Bullshop Junior]

EGR usually causes it to run rough at a idle but will smooth out some once RPM is picked up. From what he is saying and my understanding is he is getting a constant miss on his #5 cylinder.

[6bg6ga]

The MAF is not going to make the engine miss fire. It may make the engine a little rough and pop up a code. The roughness will feel much different than a miss fire

[6bg6ga]

EGR usually causes it to run rough at a idle but will smooth out some once RPM is picked up. From what he is saying and my understanding is he is getting a constant miss on his #5 cylinder.

I will have to disagree.. An improperly seated EGR will exhibit roughness regardless to rpm because of the vacuum leak and will not smooth up.

[labradigger1]

This is so true. The time has long passed when you can drive the car or truck under the apple tree and work on it yourself. With the complexity of the newer systems it takes a factory scanner costing 10 grand and up to accurately diagnose the problem. Simply throwing parts at it is totally stupid.

So far you have spent how much money? It still isn't running correctly yet is it? And your not done yet.

I am not a shade tree mechanic, i have a fully equipped garage w/ air lift and 3 tool chest full of tools and know how to use them.
As far as how much money i have thrown @ it is a little over $ 100.00, t-stat needed replaced as it was stuck open, coil was intermittenly jumping fire and needed changed anyhow. Plugs, wires,cap, rotor button, fuel filter and air filter are all maintainence items and needed changed anyways.
No, to answer your question as if it is not fixed.
I do not appreciate the sarcasam as throwing parts at is totally "stupid", i posted this question looking for advice, not to feel worse. Lab

[6bg6ga]

#5 cylinder... do a compression test

[6bg6ga]

I am not a shade tree mechanic, i have a fully equipped garage w/ air lift and 3 tool chest full of tools and know how to use them.
As far as how much money i have thrown @ it is a little over $ 100.00, t-stat needed replaced as it was stuck open, coil was intermittenly jumping fire and needed changed anyhow. Plugs, wires,cap, rotor button, fuel filter and air filter are all maintainence items and needed changed anyways.
No, to answer your question as if it is not fixed.
I do not appreciate the sarcasam as throwing parts at is totally "stupid", i posted this question looking for advice, not to feel worse. Lab


How do I know your not a shade tree mechanic? Have I met you? no I haven't. Sorry, its hard to tell someone in a thread how to fix something. Everyone always thinks they know more even with moderate experience. Have been a mechanic and I am qualified and certified. Generally people will somewhat zero experience seem to simply go to their little parts store use the $100 scanner and go by the generic untrue codes that pop up.

My suggestion now is to perform a compression test on at least the bad cylinder if not all and record the findings.

[Finster101]

Okay, if we are done bashing mechanics lets see if we can help. You said #2 plug looked off compared to the others. Do a compression test and see if it's low in that cylinder. Check the fuel pressure, the pump getting weak is a possibility. Clean the MAF with a little carb spray, gently is the key here. Try those and see what you come up with.

These types of threads are sometimes pretty difficult, as it's real hard to fix a vehicle over the phone. Sometimes it's a common failure that guys who turn wrenches everyday see and can recommend a fix, sometimes not. Most of what you have done would be considered maintenance. You have already spent a bit of money on it with things that certainly don't hurt to replace. Before you throw some expensive hard parts at it take it to a shop and get it diagnosed. I also note that in these threads we professional technicians rate right up there with lawyers and used car salesmen.

James

[labradigger1]

Cylinder #5 is not showing anything wrong, plug looks clean and correct color, no oil either. Only plug that looked iffy was #2 cyl, black sooty indicating weak or intermittent spark. Changed plugs and wires, soot went away. Have not checked to see if egr is sealed and acting correctly. Pcv valve is good.
Sorry for the retort, i'm irretated over not getting anywhere. Running out of time working on it as going to deer camp tomorrow. Wv's buck season starts monday and REALLY need my truck.

[Bullshop Junior]

Maybe try dumping some wd-40 in the gas tank. :kidding:

[Finster101]

Low compression in # 2 can also cause your plug to look like that. I will not show right away with a new plug. If you have a compression tester and it comes out okay then you have lost nothing but a little time, also if it passes you will know you do not have a valve train issue.

[6bg6ga]

Cylinder #5 is not showing anything wrong, plug looks clean and correct color, no oil either. Only plug that looked iffy was #2 cyl, black sooty indicating weak or intermittent spark. Changed plugs and wires, soot went away. Have not checked to see if egr is sealed and acting correctly. Pcv valve is good.
Sorry for the retort, i'm irretated over not getting anywhere. Running out of time working on it as going to deer camp tomorrow. Wv's buck season starts monday and REALLY need my truck.


First of all not rying to bash anybody. Sorry, thought someone mentioned #5 cylinder. Its number #2. Like I said before the MAF can be unplugged and engine will run a tad rougher and you will see a difference in the open loop and closed loop operation. Its not the MAF.
Have you put a vacuum gauge on it? If not I would try that. Also, just for grins take some gumout and spray along the manafold gaskets and see if there is any difference. Do this next to the EGR also.

[Bullshop Junior]

First of all not rying to bash anybody. Sorry, thought someone mentioned #5 cylinder. Its number #2. Like I said before the MAF can be unplugged and engine will run a tad rougher and you will see a difference in the open loop and closed loop operation. Its not the MAF.
Have you put a vacuum gauge on it? If not I would try that. Also, just for grins take some gumout and spray along the manafold gaskets and see if there is any difference. Do this next to the EGR also.

I did mention number five. Im talking with some guys on another forum about a truck missing on #5 and got the 2 conversations mixed up. Oddly enough they are both the same year range trucks with same engine. My bad. Sorry for confusing everyone.

[6bg6ga]

If your scanner is capable of doing this I would pull up the readings (fuel) from the bank with the number 2 cylinder and compare with the other side.

[labradigger1]

I have sprayed ether around everything on the top end w/ no change to rpm.
i have not performed a compression test or vacuum test yet.
it is finally light enough here to sight in some 240 grn xtp's i loaded this morning for my SRH. Thanks for the replies fellas and sorry if i am short tempered today, Lab

[6bg6ga]

Wish I was there to lend a hand. Its harder to tell someone what to check in a thread. Being there is kinda automatic to simple go thru checks and tests without a second thought.

[lancem]

I'm not sure if the 03 4.3 is like the 99 and earlier 4.3, but I've a lot of experience with them. Since you have checked/replaced most of the ignition parts I'm thinking it is fuel related. Check fuel pressure first, it needs to be 40+ psi if not time for a fuel pump, which is what it sounds like to me. If that is good I would pull the top off of the intake manifold. The vortec 4.3's use a spider injector system, the spiders are plastic and eventually get holes and leak directly into the manifold, causing rich running cylinders and in general bad running. It looks daunting but is pretty simple pulling it and replacing the spider if necessary, the inside of the intake will be carboned up, what to look for are clean areas where the leaking gas has cleaned the carbon off, got clean areas you have leaks.

[Full Mold Jack]

It may be the crank position sensor.

[Postalpaul]

My 2000 4.3 v6 was a great rig !
I could not run anything other than GM cap and rotor and also wires
Aftermarket did not last 6 months, truck would start missing throwing the exact same code
Cap and rotor I trace back to ac line ran right over distributor it would build condensation an drip on cap. When the cap is hot boom a hair line crack!!!

The only other trouble I had was crankshaft position sensor would cause it to run rough, changed it at 220000 miles smoothed right out.

Truck had 242000 miles running right till my son ran a red light and got TBoned

Hope this helps and good luck


To all the thread ninjas find another thread guy wants help !

[Jailer]

Check for a broken rocker arm.

[tomme boy]

Injectors in the intake are leaking. VERY common on early Vortec motors. Pop the top off and look. Or do a leak down test on the fuel system. That will tell right away.

[tomme boy]

Oh ya, make sure ALL of the ground wires are still hooked up.

[sparkz]

I would look to spark issues,, and remember this if nothing else

recheck spark routes and cap / rotor and bearing for dist shaft.
JUST CUZ ITS NEW DON'T MAKE IT GOOD,, Point of fact it's UN-Tested and not Road proven

I have over years install a ton if stuff to find it bad or fails shortly after, so recheck your work and parts

(dist. is plastic, is it broken where the screws hold cap down?
and is cap seated? screws brake the ears on dist when ya remove the torx dist cap hold down screws)

Try wetting it down at night in dark watch for corona spark leak, use a spray bottle,
check bottom for rotor for high voltage burn thu,


It's a bitch to take it in and find out they replace your new/er part/s and fix it

Get a Fuel pressure gauge and run it and check running and shut it off check for leak down if check valve and injector leaking, most ya can crimp off the return (Plastic) line for the injector test, check Mitchel manual for specs.

(I installed a premium cap and rotor and a 100 miles from home at 2 weeks later motor "Shut Off" on the Big road, had a TOW, and a repair done for $200 and guess what?? Caps dead!!! yeha I got the better one too,, guy Installed new cap and I drove to get my $20 back for cap),, Ouch.... Check work you have done...


A good scanner can shut down one cyl at a time and locate the prob to where to look if all else fails
Patrick

[HeavyMetal]

Reson I suggested Injector issue:
93 caprice, ex cop car with the LT1 engine in it, ran good would smoke tires 150 feet or more! Both of them!

Bought it at an auction $1500 drove it a couple years and then the wife passed, suddenly I got four cars and one License!

Sold some off kept the Contour for mileage reasons, drove the Caprice weekends eventually parked the Caprice for more than a year.

When I went to restart it it ran like **** missing on every cylinder all the time!

Spent most of a week trying to sort it out, then one of the guys at work who was, and still is, a big chevy racer suggested I pull the injector manifold ( fuel rail) and remove the injectors because he was told of a re issue of O rings on the injectors with a new material chevy was touting as the latest greatest break through since sliced bread!

Cost me 30 bucks at the Chevy dealer and 2 hours after work pulling and replacing the fuel rail and injectors.

Washed my hands sat behind the wheel and turned her over, started instantly and ran perfectly! No miss no hesitation just power like the day I bought her.

Now I don't claim to be a trained mechanic but I have been in the service end of the sweeping scrubbing industry for 15 years and sales end for the last 18 and what I can tell you is 80% of the time your issue is a simple one you've just overlooked!

I've seen it happen every day when customers bring in thier battered machine and say it won't run and they can't fix it.

One out of ten have an empty LP tank! Should see the look on thier face when we put on a fresh tank and it starts and runs fine!!!

If you haven't already done this pull the fuel rail and injectors and replace every O ring you can find and put it back together and try it.

If that doesn't work then proceed to other issues such as fuel pump and then, and only then, suspect an internal parts failure.

[monge]

fuel spider its the injectors reg and its under the manifold eASY TO CHECK PUT A FUEL PRESSURE GAUGE ON FUEL RAIL USE A CLAMP TO PINCH OFF RETURN LINE AT TANK TURN INGITION ON FUEL PRESSURE SHUOLD HOLD IF NOT REPLACE FUEL SPIDER1

[geargnasher]

Lots of guessing and a couple of people who actually know what sort of systems are under the hood of a 2003 4.3L Chevy. The rest of you who don't have a clue can butt out please.

If the ONLY trouble code present is a P0300, (random or multi-cylinder misfire), then the CMP, CKP, Knock, O2, TPS, MAF, IAT, and ECT are likely ok, so no throwing parts at it, OK? What you're looking for is a mechanical failure or failure in a non-continuously-monitored circuit.

The "spider" or CFI pod is prone to leaking fuel inside the intake manifold via hardened injector solenoid body o-rings. A more common cause of internal flooding is a blown diaphragm in the fuel pressure regulator located on the side of the CFI pod underneath the plastic upper intake manifold on the passenger side. Quickest way to tell is to pull off the throttle body or use a bright flashlight and pocket mirror with the throttle held wide open to observe any washing of the lower intake manifold under the fuel pressure regulator vent tube. Look for a clean, washed-out circle about 2" in diameter under the regulator (all else inside will be oily black carbon-coated). If you see that, pull the plastic upper intake and replace that part first.

Code readers are limited in that most of them cannot give you live data. This is where a REAL scan tool can save hours of guesswork: Look at left and right bank short-term and long-term fuel trim numbers, adaptive fuel cell ID, misfire counters, EGR pintle position, etc. etc. to help pinpoint what's going on.

If you don't have any P0171-2-3-4 codes present, or any P100-series codes you likely aren't over- or under-fueling or leaking vacuum, so based on only the symptoms and the P0300 I'm leaning toward a stuck-open EGR valve or broken cyl #2 intake valve spring rather than a sensor failure or a problem with fuel delivery, fuel pressure, spark, or air. GM fuel pumps get weak and the regulators that operate on the return-side do fail, but usually such failure is accompanied by fuel trim-related codes and the engine won't do much more than idle and will often backfire when accelerated. Usually a fuel pump just quits all at once when it fails, loss of fuel pressure is more often a regulator problem.

When cats plug up, the backpressure causes all sorts of running problems but oddly rarely causes any codes to set other than misfire, and then usually only on one bank. This could still be your problem. If you don't find a broken rocker arm or VALVE SPRING on #2 Intake, pull the passenger side, upstream oxygen sensor out of the pipe and let it dangle (plug it back into the harness after unscrewing the sensor and before starting) and see if the running problem doesn't go away. If that doesn't do it, pull out the EGR valve and see if a chunk of carbon about the size of a kitchen match head isn't stuck in the pintle.

If it isn't a valve train problem, plugged cat, or stuck EGR, take it to a good mechanic and make sure to tell him/her how much money you're willing to spend on diagnostics (plan for minimum two hours at the shop's labor rate) and be prepared to pay for a part or two as part of the solution to the problem, sometimes there are multiple issues that require certain things be fixed before continuing diagnostics. Remember also that when you go to a repair shop you are paying for the many thousands of dollars worth of scan/diagnostic equipment and for the years of accumulated training, systems knowledge, and experience of the mechanic, which is often something that's really still quite cheap even at ten times the price you'll pay for it. PM me if you have any further questions, maybe we can get it going this weekend.

Gear

[torker]

I'd bet Gear hit the nail on the head with the EGR Valve. I'd lift the EGR plunger off it's seat and listen for an engine stumble. if the engine stumbles when you do this, Then release the plunger and let it seat back down. If the engines continues to stumble remove the valve and clean the plunger and seat. A rag with some carb cleaner will work. hope it helps.

[labradigger1]

Whew! What a pile of advice. Thanks to all. I changed the plugs again this morning, rechecked firing order. Engine runs a little better, idles rough and falls on its face when put in gear and pressing accellerator an dholding brake. Drove it up the road @ WOT and run fair, check engine light will flash for a few seconds then remain on. Cleared codes and ran it again, p0300 still present and missfire cyl#1. Changed #1 wire and plug, installed spark tester and it will jump a spark about 7/8". Ran @ all rpm's and NO missfire is present on any cylinders. Do not have time to do a compression test, fuel bleed down, fuel pressure or check the spiders this weekend. Thank you all for the advice, Lab

[Hogdaddy]

Check rotor button as already mentioned,,I bought one that was bad and if I did'nt take dist cap off I would have never known.. Good Luck

H/D

[Lloyd Smale]

not your post so id be carefull tellilng people to but out. When im having a problem with a sixgun im sure willing to take advice from a man that isnt a gunsmith. I was an electritain all my life but sure know that theres people that arent electricians that know the answer to electrical questions. Ive also seen auto problems that many so called expert mechanics couldnt solve. Im sure if he wanted just advice from licienced mechanics he wouldnt have posted that question on a bullet casting fourm!
Lots of guessing and a couple of people who actually know what sort of systems are under the hood of a 2003 4.3L Chevy. The rest of you who don't have a clue can butt out please.

If the ONLY trouble code present is a P0300, (random or multi-cylinder misfire), then the CMP, CKP, Knock, O2, TPS, MAF, IAT, and ECT are likely ok, so no throwing parts at it, OK? What you're looking for is a mechanical failure or failure in a non-continuously-monitored circuit.

The "spider" or CFI pod is prone to leaking fuel inside the intake manifold via hardened injector solenoid body o-rings. A more common cause of internal flooding is a blown diaphragm in the fuel pressure regulator located on the side of the CFI pod underneath the plastic upper intake manifold on the passenger side. Quickest way to tell is to pull off the throttle body or use a bright flashlight and pocket mirror with the throttle held wide open to observe any washing of the lower intake manifold under the fuel pressure regulator vent tube. Look for a clean, washed-out circle about 2" in diameter under the regulator (all else inside will be oily black carbon-coated). If you see that, pull the plastic upper intake and replace that part first.

Code readers are limited in that most of them cannot give you live data. This is where a REAL scan tool can save hours of guesswork: Look at left and right bank short-term and long-term fuel trim numbers, adaptive fuel cell ID, misfire counters, EGR pintle position, etc. etc. to help pinpoint what's going on.

If you don't have any P0171-2-3-4 codes present, or any P100-series codes you likely aren't over- or under-fueling or leaking vacuum, so based on only the symptoms and the P0300 I'm leaning toward a stuck-open EGR valve or broken cyl #2 intake valve spring rather than a sensor failure or a problem with fuel delivery, fuel pressure, spark, or air. GM fuel pumps get weak and the regulators that operate on the return-side do fail, but usually such failure is accompanied by fuel trim-related codes and the engine won't do much more than idle and will often backfire when accelerated. Usually a fuel pump just quits all at once when it fails, loss of fuel pressure is more often a regulator problem.

When cats plug up, the backpressure causes all sorts of running problems but oddly rarely causes any codes to set other than misfire, and then usually only on one bank. This could still be your problem. If you don't find a broken rocker arm or VALVE SPRING on #2 Intake, pull the passenger side, upstream oxygen sensor out of the pipe and let it dangle (plug it back into the harness after unscrewing the sensor and before starting) and see if the running problem doesn't go away. If that doesn't do it, pull out the EGR valve and see if a chunk of carbon about the size of a kitchen match head isn't stuck in the pintle.

If it isn't a valve train problem, plugged cat, or stuck EGR, take it to a good mechanic and make sure to tell him/her how much money you're willing to spend on diagnostics (plan for minimum two hours at the shop's labor rate) and be prepared to pay for a part or two as part of the solution to the problem, sometimes there are multiple issues that require certain things be fixed before continuing diagnostics. Remember also that when you go to a repair shop you are paying for the many thousands of dollars worth of scan/diagnostic equipment and for the years of accumulated training, systems knowledge, and experience of the mechanic, which is often something that's really still quite cheap even at ten times the price you'll pay for it. PM me if you have any further questions, maybe we can get it going this weekend.

Gear

[labradigger1]

I dont think i am blind BUT, darned if i can find the egr valve, most 4.3 engines have it located just in front of the t-stat housing. No pipe/hose coming from exhaust manifold either

[Lloyd Smale]

Ill give you another UNEDUCATED idea. We ran alot of 4.3s as meter trucks at work and the ealier ones had a problem with the balancer slipping on the crank shaft. It made them run like **** and shake like ****. I can remember at least 3 of our trucks having that happen to them.

[Bullshop Junior]

I dont think i am blind BUT, darned if i can find the egr valve, most 4.3 engines have it located just in front of the t-stat housing. No pipe/hose coming from exhaust manifold either

On both of my 4.3s, the EGR valve is under the intake manifold, kind of behind and above the water pump. A little tight to get to.

[geargnasher]

not your post so id be carefull tellilng people to but out. When im having a problem with a sixgun im sure willing to take advice from a man that isnt a gunsmith. I was an electritain all my life but sure know that theres people that arent electricians that know the answer to electrical questions. Ive also seen auto problems that many so called expert mechanics couldnt solve. Im sure if he wanted just advice from licienced mechanics he wouldnt have posted that question on a bullet casting fourm!

Be sure and check the magazine follower on your sixgun, I had problems with mine because it was getting dirty and binding.

The man DID ask for a "Chevy mechanic", in the title no less, and there are plenty of qualified automotive technicians and hobbyists who are members here. There are also a bunch of folks who, because they have no vested interest in the OP's time, busted knuckles, or money, like to venture WAGs that only serve to confuse the issue no matter how well-meaning they may be. These kinds of automotive issues are confusing enough without true, educated advice being given. If you don't REALLY know what you're talking about, you are doing this man a disservice by throwing WAGs at him. Many here have already posted knowledgeable, helpful advice, but most have not because they simply don't have the background.

Gear

[w5pv]

They don't make timing chain/gears like they use to.Check timing.Just had one with the same symptoms cost about $600 to repair.

[6bg6ga]

I think I remember telling you to check the EGR in post #13

[Lloyd Smale]

id bet 75 percent of the guys here have wrenched on a chev or have done enough back yard mechanicing to comment on a "why is my motor missing" thread. Like ive said ive seem certified mechanics that struggle with easy stuff and i guess i have to ask who is qualified to rate on here whos a "chev mechanic" and who isnt. I dont have all the high tech equiptment needed today to diagnost and fix cars. I have back in the day restored cars and ive rebuilt a half a dozen small block chevs and one big block. I dont have a certification but sure as hell know what makes a motor run. Again i will say that theres a good many on my level here so before you slam someones post and think hes causing troubles because he isnt right i have to ask you in your carreer as a mechaninc have you ever guessed wrong?? I know if i had a problem i didnt know the answer too id want all the opinions i could get. even from the guys that arent qualified. Might be that just one of them had the same thing happen to them at one time.
Be sure and check the magazine follower on your sixgun, I had problems with mine because it was getting dirty and binding.

The man DID ask for a "Chevy mechanic", in the title no less, and there are plenty of qualified automotive technicians and hobbyists who are members here. There are also a bunch of folks who, because they have no vested interest in the OP's time, busted knuckles, or money, like to venture WAGs that only serve to confuse the issue no matter how well-meaning they may be. These kinds of automotive issues are confusing enough without true, educated advice being given. If you don't REALLY know what you're talking about, you are doing this man a disservice by throwing WAGs at him. Many here have already posted knowledgeable, helpful advice, but most have not because they simply don't have the background.

Gear

[6bg6ga]

Why don't we move on? I mentioned many posts ago to check the EGR valve somewhere around post 13 or so. Why did I mention this?
The reason is I generally rule out the easy things first as well as the most obvious. I may have improperly made a comment about throwing parts at the situation in hopes of a cure and if I did I do apologize for this. Looking thru the posts it is obvious that the thread starter did replace items that did need replacing. As for my qualifications... have certification but not currently in this field. Have years of machining experience as well as electronic experience. Have built a number of engines over my lifetime so far. These engines are of the Ford, Chevy, and Pontiac variety. Currently have my toy in the garage that is a supercharged 4th gen Z-28 that runs low tens is street legal and smog legal. Am experienced in GM tech tools as well as most if not all aftermarket computer programs. Changed my 93's computer to a OBD2 and programed it to supply the correct spark and fuel maps to an engine that runs with 18-20 lbs of intercooled boost with 60lb injectors.

My suggestion at this point in time is to check the EGR valve. Its difficult to get to but not as bad as the GMC and Chevy vans that I have owned. I would certainly do this before thinking about pulling the intake manafold. Sometimes you can gently tap on the outside of the EGR and it will seat.

[Lloyd Smale]

With your level of experience id trust your diagnosis over any certified mechanics in my area. Most of them check a code and look in the book to see what it might be and start throwing parts at it.
Why don't we move on? I mentioned many posts ago to check the EGR valve somewhere around post 13 or so. Why did I mention this?
The reason is I generally rule out the easy things first as well as the most obvious. I may have improperly made a comment about throwing parts at the situation in hopes of a cure and if I did I do apologize for this. Looking thru the posts it is obvious that the thread starter did replace items that did need replacing. As for my qualifications... have certification but not currently in this field. Have years of machining experience as well as electronic experience. Have built a number of engines over my lifetime so far. These engines are of the Ford, Chevy, and Pontiac variety. Currently have my toy in the garage that is a supercharged 4th gen Z-28 that runs low tens is street legal and smog legal. Am experienced in GM tech tools as well as most if not all aftermarket computer programs. Changed my 93's computer to a OBD2 and programed it to supply the correct spark and fuel maps to an engine that runs with 18-20 lbs of intercooled boost with 60lb injectors.

My suggestion at this point in time is to check the EGR valve. Its difficult to get to but not as bad as the GMC and Chevy vans that I have owned. I would certainly do this before thinking about pulling the intake manafold. Sometimes you can gently tap on the outside of the EGR and it will seat.

[labdwakin]

I don't know if this is any help, but the newer GM vehicles have distributors with plastic housings. I would check and make sure there isn't any slop in the shaft as it relates to the housing.

[sparkz]

I Only made mention of a few tips as OUR 4.3 had issues like hes talking about and spoke to what our fix was,, I spent years working on autos and heavy trucks / off road equpt, before I Was a 20year electrical contractor, and tho i would not advise anyone to shovel parts / money at it, I gave advice as to some easy things to check, that might not be read by a scanner that he could do and check,,

Patrick

[bobthenailer]

#5 cylinder... do a compression test

also do a running compression test ! remove spark plug, grd sparkplug wire, install compression tester in suspected cyl start engine & compair readings with a known good cyl.if suspected cyl is lower ck for broken valve spring.
IN the 1990s 4.3 engine a partialy stuck open EGR valve would cause a rough idle & sometimes stalling at idle.

[labradigger1]

Thanks for all the replies, i have been out of town @ deer camp w/ my dad since sunday. Rough hunting weather this year and game not moving, did get an 8pt an dmy dad got a 3 pt. Somehow i missed a buck broadside @ 25 yds w/ my 44 mag SRH, still trying to figure that one out. Anyhow, i have not wrenched on the truck for several days but will again fri or sat as i am going to hunt locally for a couple days, still need to fill a buck and doe tag. Thanks again, Lab

[opos]

Would a leak down test be valid in this case?

[tomme boy]

For the fuel system, yes.

[bandit7.5]

‹<<<<<<<<<<<<<<<<< owner/operator of a 1965 Chevy c10 long bed Positively rusty. I will not drive by wired sensores. Too much to go wrong. Also it pizzles the local greenie down the road that I still drive it.

[labradigger1]

Ok fellas, only getting to wrench on it piecemeal, today i performed a fuel leakdown test. Psi running is 50, no drop in psi after shutoff. Pulled valve covers and checked for bad rocker arms, broken valve springs etc, everything else looks ok. Next thing i will check is the egr, evidently it is located underneath the intake manifold an di do not have time to drain dexcool an dpull intake today. Thanks for the help thus far, Lab

[geargnasher]

I dont think i am blind BUT, darned if i can find the egr valve, most 4.3 engines have it located just in front of the t-stat housing. No pipe/hose coming from exhaust manifold either

That's right. Yours must not have it. One less system to eliminate.

Do a compression test. You also could have a poppet nozzle that layed down on you. Does your "scanner" show real-time fuel trim percentages?

Gear

[labradigger1]

That's right. Yours must not have it. One less system to eliminate.

Do a compression test. You also could have a poppet nozzle that layed down on you. Does your "scanner" show real-time fuel trim percentages?

Gear
Yes, i believe it does but i cannot figure out how to make the scanner work w/ the engine running

[geargnasher]

RTFM.

STFT and LTFT for each bank have a +/- 25% limit and a time at that limit before setting rich/lean codes. If it's trimming single digits for all four you probably don't have a stuck injector, but it you do, the fuel trim correction will alter injector on-time for an entire bank until the O2s are happy. That's what it's designed to do. If you have a cylinder that isn't fueling OR one that isn't firing, the exhaust oxygen will be high either way, causing a lower voltage signal from that bank's O2 sensor and the computer will correct by adding fuel to the whole bank. The emissions requirements may be met, but the whole bank may be out of whack from a running standpoint and you can tell by looking at the the injector ON-time pids with your scanner.

Also be sure you didn't crosswire #1 and #3 at the cap.

Gear

[6bg6ga]

Did you ever get it running correctly or figure out the problem?

[labradigger1]

No it is still not correct.
I changed the spider injector assembly and that did nothing to help.
fwiw since i changed the spider assy i have no instruments now, no odometer either. I have checked all connections and all fuses. I swear i am about to burn it to the ground and open up a few clips of ak47 on it.
It has a new distributer cap, wires and rotor button on it but NOT GM.
I swear it acts like a bad wire. I am going to install a new gm dist, rotor button and wires next. After that i give up. Going to take it to a gm dealer next.
Lab

[6bg6ga]

Did you ever check the egr valve?

[labradigger1]

Did you ever check the egr valve?

As near as i can tell it does not have an egr system. No pipe from exhaust manifold, not anywhere around the water neck as on other 4.3's.
I wish it was the egr.
Lab

[6bg6ga]

As near as i can tell it does not have an egr system. No pipe from exhaust manifold, not anywhere around the water neck as on other 4.3's.
I wish it was the egr.
Lab

Well, I just Googled it and its supposed to have one. Should look like a solenoid on end with an electrical connector on the end.

[labradigger1]

Well, I just Googled it and its supposed to have one. Should look like a solenoid on end with an electrical connector on the end.
You are correct, google does say it has one. Hayes repair manual shows one as well next to the water neck. I assure you that there is not one there, if it had an egr it should also have a heat riser pipe from the manifold going to it, it does not. My 4.3 is the x engine code and it is my understanding w/ the x code w/ cfsi they do not use egr system. 4.3's w/ the w code do however.
Lab

[double8]

My 4.3 had similar issues.....could never find out what the cause was. Traded it in before I threw good money after bad. Cheaper in the long run.

[abunaitoo]

I've had lots of problems with these engines.
Take a compression reading. Lots of head gasket, and cracked head problems.
EGR valve is a common problem on these. It's electric, not vaccum, so no piping is visible. Feeds through the intake manifold. I've attached a picture of the 91978
EGR is easy to get to once you see it. Take it out and make sure the pintel is seated.
This engine also has problems with intake manifold corrosion.
And... The plastic plenum sometimes cracks.
I normally checks the EGR first because it's easy to get to.
It it checks ok, then I take a compression reading. Plugs are a pain to get to. Go through the fender well.
Hope this helps some.
Disregard the other picture. Mistake

[labradigger1]

I've had lots of problems with these engines.
Take a compression reading. Lots of head gasket, and cracked head problems.
EGR valve is a common problem on these. It's electric, not vaccum, so no piping is visible. Feeds through the intake manifold. I've attached a picture of the 91978
EGR is easy to get to once you see it. Take it out and make sure the pintel is seated.
This engine also has problems with intake manifold corrosion.
And... The plastic plenum sometimes cracks.
I normally checks the EGR first because it's easy to get to.
It it checks ok, then I take a compression reading. Plugs are a pain to get to. Go through the fender well.
Hope this helps some.
Disregard the other picture. Mistake

I'll be darned! It does have that item, i removed it during plenum removal but did not check it out. I will look @ it wendsday as that is the next day i have off, working dark to dark now and tired when i get home. Thank you for the picture,
Lab

[6bg6ga]

I hope you can get someplace now

[abunaitoo]

I've had good luck cleaning them. Only had to change one in all these years.

[dagger dog]

The aftermarket parts offer a screened egr gasket to keep the pieces of carbon from lodging between the pintle and seat on the EGR valve.
If the pintle is stuck in the open position from a piece of carbon disloged from the intake,it will set a pintle position code in the PCM memory, read with a generic scanner it will give a P04-- , code, I think a P0404, but don't quote me.

[labradigger1]

Ok, i have today off and lucky me i got the flu. Energy is just drained. I did walk out and raise the hood and what i thought was the egr in the picture is the vapor purge valve. Have not found the egr yet. I also wanted to perform a compression test today but thats not going to happen either.
lab

[abunaitoo]

Does this help????92269

[labradigger1]

Nope, that is where my service manual shows it as well, next to the water neck. It is not there.
Lab

[abunaitoo]

How about posting a picture of the engine.
If I see which 4.3 you have, I might be able to help.

[labradigger1]

How about posting a picture of the engine.
If I see which 4.3 you have, I might be able to help.

I will try, i now have pnuemonia and it feels like i am breathing fire, we are also getting hammered by winter storm herculese. May be a couple days. Thank you for your patience.
Lab

[labradigger1]

Ok folks, i finally found time to wrech on the truck a little.
Following advice from 6b and gear i did a compression test. Cylinders #'s 2-6 were at 157#'s +/- 4 #'s.
Cyl #1 was zero!
Pulled the head and valves were leaking badly and the intake seat was worn.
Cylinder wall looked aweful, deep scratches on front and rear of cylinder.
I decided it would be cheaper to install a salvage yard engine than machine shop charges for head work, sleeve and a rebuild kit.
I installed the engine last weekend and all is good now.

Thanks to all of you for the insight and tips.
Lab

[TXGunNut]

Glad you got the old girl running. A good machine shop is hard to find these days. A good used engine is nearly as good as a factory reman.

[abunaitoo]

Glad your feeling better.
Good work on finding and fixing the problem.
Now you can get back to casting, loading and shooting.