88 Silverado 1500 350"K" Engine ECM?

[Muddy Creek Sam]

Help, Katie's truck is making me nuts. Check Engine light is always on, No Codes. Idles to High and shuts of when you slow down to turn. Anyone have any Idea's. Changed the IAC, no help.

Thanks,

Sam :D

[master caster]

Do you have a vacuum leak? Spray around with carb cleaner and see if motor reves up a little. Are you on the brakes when it dies? unhook battery and cycle key a time or too and hook battery back up and see if the light comes back on.

[dmize]

Whats the code for the check engine light.
2 very common problems are the gaskets sucking out under the throttle body and the Engine Coolant Sensor leaking and corroding the terminals inside the connector. This screw with the computer telling it to dump more fuel in the engine.

[Muddy Creek Sam]

Whats the code for the check engine light.
2 very common problems are the gaskets sucking out under the throttle body and the Engine Coolant Sensor leaking and corroding the terminals inside the connector. This screw with the computer telling it to dump more fuel in the engine.

No Codes are Thrown. Gasket is intact.

Sam :D

[geargnasher]

If the SES light is on, there is a code. Jumper ALDL pins A and B with key on, engine off. If there are truly no codes, it will flash a code "12", which is FLASH (pause), FLASH FLASH.

Gear

[Muddy Creek Sam]

Gear,

Code reader gets nothing. Light doesn't come one with key on and ECM disconnected. Comes on again with ECM plugged in.

Sam :D

[geargnasher]

Sam, put the "code reader" away for a minute. The ECM controls the ground side of the SES light circuit. If it's on when the truck is running, there is a problem. Ground the pins. If you get a 12 over and over with no other codes, THEN proceed with no-code diagnostics.

Gear

[Muddy Creek Sam]

Gear,

That is the 2 on the left hand side?

Sam :D

[geargnasher]

http://en.wikipedia.org/wiki/ALDL

Gear

[GREENCOUNTYPETE]

Do you have a vacuum leak? Spray around with carb cleaner and see if motor reves up a little. Are you on the brakes when it dies? unhook battery and cycle key a time or too and hook battery back up and see if the light comes back on.

+1 but i use an unlit propane torch and wait for it to rev

[greenbud]

+1 but i use an unlit propane torch and wait for it to rev

thats a great idea I will have to try that on My 84 monte carlo

[dmize]

Works good,but just like with carb cleaner. MAKE SURE you dont have a leaking plug wire before you start hosing things down.

[dmize]

I would still remove the 2 wire connector fron the ECT,I willing to bet its all nasty on the inside.

[thx997303]

I would guess vacuum leak, my 87' did that at one time.

But that's just a WAG.

[GT27]

With no codes present the gas cap may be venting causing this common problem believe it or not,check there first!!!:coffee:

[Recluse]

I had this issue with my '94 C-1500 extended cab (same engine). Three things:

• Gas cap leaking and affecting emissions vacuum (believe it or not).

• Oxygen sensor--a real PITA to change, and I mean a REAL pain. It's underneath, on the exhaust assembly right before it goes into the catalytic converter. The GM "engineers" in their infinite wisdom decided you didn't need ANY length on the wire, so you have no room to negotiate the hookup process.

• Exhaust Gas Recycle Valve (EGR) valve. Inexpensive, easy and quick to change and this eliminated the revving of the engine along with the stuttering and trying to die at slower speeds.

:coffee:

[Muddy Creek Sam]

Sam, put the "code reader" away for a minute. The ECM controls the ground side of the SES light circuit. If it's on when the truck is running, there is a problem. Ground the pins. If you get a 12 over and over with no other codes, THEN proceed with no-code diagnostics.

Gear


got a 12 one time.

Sam :D

[Jailer]

intake gasket

[Dark Helmet]

Does this model have a plastic intake manifold? They are known to crack and leak.

[Boondocker]

vacuum leak

[thx997303]

No that model is not a vortec engine. It has a metal intake manifold.

[geargnasher]

got a 12 one time.

Sam :D

Does it rev/stall every time the brake is pressed? It could also be swallowing a load of brake fluid from a leaking master cylinder seal, which would account for the right turn thing, the vacuum line attaches to the right side of the booster.

If it were any other vacuum leak it would be more consistent. Throttle shafts wear out on those causing leaks there and erratic or high idle, but even a brand new one leaks some and that's accounted for in the IAC programming.

EGR can cause stalling problems and is quite common on these. Chunks of carbon can stick in the egr valve pintle, but usually when that happens it won't idle at all until you manually flex the valve to dislodge the carbon chunk. The egr control solenoid could be on the fritz, and the injector wiring can short or break inside the insulation where it goes through the grommet under the air filter housing riser.

Other things that can cause it are leaking throttle body gaskets causing internal fuel leaks, bad fuel pressure regulator diapragm, wiring/connector issues, intermittent/bad ECM ground on the thermostat housing, ESC problems, cam sensor (reluctor) problems, ignition module problems, any number of things. If you had a bad or out of range sensor somewhere or some broken/chaffed wiring to a MONITORED circuit, it will set a DTC. Problem with OBD I systems is the computer does very little continuous monitoring of circuits, so lots of things can go bad and the computer has no idea. OBD II has about 1200 codes and multiple continous/non-continous monitors that can store three different priorities of trouble codes, and that gives the technician a much narrower area to look at first when diagnosing SES light issues.

I wonder if you noticed the SES light on after the engine died, or when it was still running? Any time the key is on and the distributor stops turning (pickup signal flatlines) the ECM turns on the light. It should also do about a 4-second "bulb check" when you start it up and then extinguish.

Gear

[Lloyd Smale]

if the check engine light is on with no code id be thinking its your ecm that is bad

[Jim Flinchbaugh]

Eliminate the dumb stuff first OK?
IF it will stay idling, stick you fingers under the EGR valve and lift it off its seat. IF it does not change anything, the valve is leaking and needs replaced. If it stalls the engine, it is sealing and OK. 02 sensors go bad, dont always throw a code. The other thing that will drive those engines nuts is the knock sensor. Located in the bottom of the block below the motor mounts, single blue wire going to it. Unhook the wire and try running the truck.
Do you have a vacuum gauge?
hook it up to MANIFOLD vacuum, and see what it reads, is it steady or jumping around?
if steady and above 12-13 the engine should run. Now, while the vac gauge is still hooked up, run the engine up to about 3000 rpm and hold while Watching the gauge. does it go up then start going *lower & lower or hold steady? Allow the engine to idle again, snap the throttle up to about 3000 again and let it drop while watching the gauge, it should snap up on the throttle drop and then return to normal in a second, if it hangs "up" for 2-3 seconds, or the engine bogs down in the first part of this routine*, your cat convertor is plugged up. if the vac gauge is jumping around at idle , you gotta bad intake or exhaust valve.

The first thing you should always do in diagnosing and engine, is a compression or leak down test. You have to verify the engine is mechanically sound enough to run properly otherwise you're pi***ng in the wind

[fishhawk]

on a 88 that was before the "black box" once the check engine light comes on don't turn the vehicle off read the code before you turn it off or it won't throw a code!

[dmize]

Actually "the box" /PCM is silver,and if there is a check engine light there is
one.
If the light comes on it will store a code UNLESS someone
A. Unhooks the battery or it looses battery power
B. UNPLUGS the PCM
C. Trys to read the codes and doesnt know what they are doing
If any of this is done the code is lost forever untill the fault occurs again and resets the light.

[geargnasher]

Dmize, that depends on whether the code is classified as "ignition-latched" or "non ignition-latched". Some codes, particularly EGR and O2 codes, will vanish when the key is turned off. If you jumper the pins with a paperclip while it's running, that initiates a different test called "ritch/lean" that makes the SES light flash. More off than on, lean. More on than off, rich. Very scientific. The only way to get ignition-latched codes is with a reader or scan tool on that particular ignition cycle, but I wanted Sam to verify a true "no-code" condition before barking up the wrong tree with assumed data. Code readers don't always do what they should.

Jim F., if it's intermittent that pretty much eliminates base engine condition.

Gear

[Blammer]

my code reader for OBD1 is a paperclip

[Muddy Creek Sam]

My reader is a CanOBD2&1 Craftsman model 89.20899.

Sam :D