Diesel engine question.

[JeffinNZ]

Team.

My Isuzu Bighorn (Trooper) is a four cylinder 3.1 litre diesel. From cold it starts great but once warm can take a bit of turning over. All starts are done with at least one cycle of warming the glow plugs, mostly two cycles. Any ideas what is going on?

[Norbrat]

My first guess is valve clearances. Thermal expansion lengthens the valve, closing the gaps, means the valve is not seating, compression leaks, etc.

I've had this with other engines (not just diesels).

[Catshooter]

Jeff,

I know zip about diesels. But since I saw the headline about NZ having another quake I'm very glad to see you posting. Was concerned.


Cat

[starmac]

I don't know ANYTHING about the little isuzu powerplant, but when the ford (internationals started starting hard when warm, you could pour cold water on, or pack snow around the injector pump and she would light off. But your wallet was fixing to get a little lighter in the form of a new one.

[Phoenix]

Isuzu troopers are one of my passions. I have three. I have one of the 86s with the 2.2L turbo diesels. and three other diesel pickups. This can be indicative of an air leak If there is a small leak in the fuel line on the inlet side of the injector pump. It may not show a fuel leak but if it can suck even a little air after the engine stops. It would only have the affect when it is hot/warm as the expansion allows the air in but not enough to leak much/any fuel. When you shut the engine off a bubble forms in the inlet side of the injector pump which makes it hard to start. When it is cold the affect will not be present. The real question is where is the air getting in. My ford 6.9L diesel had a similar issue. I had to loosen and retighten all fittings from the water separator to the injector pump. The problem turned out to be between the fuel filter and the injector pump. Mine has a air bleeder on the fuel filter to get air out of the line after changing the filter. It is a small schrader valve on the filter housing. That I am pretty sure is where my problem turned out to be. Sometimes changing the filter and schrader valve is all that is needed. (if you dont know what a schrader valve is it is the same type of valve on your tires) Those are easy to check/change as compared to having a good set of line wrenches to loosen/tighten the fuel lines to see if they are the problem. The thing you dont want is for there to be a small leak in one of the gaskets in the injector pump as this normally requires it to be rebuilt/replaced.

I would try changing the fuel filter and bleeder valve first as they are inexpensive and easy.

[Driver man]

I dont know about Isuzu but Ive had this problem a few times in 3L Hiace . Clogged fuel filter due to diesel bug and very very dirty air filter. What mileage on the clock.

[Pb2au]

+3 on fuel delivery. The odds are on you are bleeding off fuel in the system.
Look for leaks around the injectors, fuel lines etc etc. It also could be sucking air at a line as well. Most diesel issues can be traced back to fueling.
The other thing is this; Does the issue present mostly when it is cold out? If so, it could be that your glow plugs are not going on long enough, or at all. I would also check their functionality as well.

[oneokie]

Do not know who makes the fuel system on the Isuzu, but will say this; The RoosaMaster injection pumps used on JD tractors will act the same when the clearances in the main injection pump get loose.

[starmac]

Like I said before, I know nothing about an isuzu, but cat,cummins,detroit,international,case, john deere etc all with a small air leak in the fuel system will cause a hard start or even a no start. The harder the longer it sets as the fuel has more time to drain back to the tank. Usually they will be hard first thing in the morning and easier the rest of the day. Sometimes these very small air leaks are hard to find. I keep some some short test lines made up of clear tube to install in varying places to narrow down the air leak, but have had to pressurize the system enough to make it leak fuel to find them too.

[Phoenix]

My ford 6.9 still has a minor issue that is caused by the same thing. If I park it on level ground no problems, Front end facing downhill no problems, Front end facing uphill. Very hard start. (longer it sits the worse) It is an air leak that is letting the fuel run back to the tank and creating an air bubble in the line. Sometimes you can troubleshoot these problems by simply parking it so the engine is lower than the fuel tank. if it starts right up then you know you have an air leak somehwhere.

[a.squibload]

(Non-diesel comment)


My first guess is valve clearances. Thermal expansion lengthens the valve, closing the gaps, means the valve is not seating, compression leaks, etc.

I've had this with other engines (not just diesels).

My KLX250 (4-stroke) was fixed by lapping the valve pucks a little,
allowing the valves to close properly. Starts easier now and feels like
more torque.

Back to 2-strokes...

[tomme boy]

Are you saying that it turns over hard as in it labors, or has to let it keep turning over?

If it is turning over hard, check the battery cable connections on BOTH ends of the cables. I had a older car that once it heated up, if it shut off you could not start it again till it cooled off. Turned out to be the (+) cable going to the starter. The cable itself was very badly corroded under the cover. I was watching a friend try to start it, And I noticed the cable was flexing around when he tried to start it. I put my hand on it and it was HOT. Almost to the point of melting the plastic. I replaced that cable and it fixed it. I fought that thing for two years before I fixed it. It was a 68 Camaro that I only drove in the summer on nice days. I change out the starter 4 times and was about to buy one of the gear reduction type starters. A $5 cable made me really mad. So check easy stuff first.

[starmac]

My ford 6.9 still has a minor issue that is caused by the same thing. If I park it on level ground no problems, Front end facing downhill no problems, Front end facing uphill. Very hard start. (longer it sits the worse) It is an air leak that is letting the fuel run back to the tank and creating an air bubble in the line. Sometimes you can troubleshoot these problems by simply parking it so the engine is lower than the fuel tank. if it starts right up then you know you have an air leak somehwhere.

99.9% percent of the time on the 6.9/7.3 idi engines, it is the return line caps and o'rings on the injectors, causing this problem. On the models with the water separator next to the brake booster, it too was a common culprit and could be fixed by plugging the hose in the bottom of it. Both common problems are relatively cheap and easy fixes.

[Phoenix]

I just havnt bothered to mess with it. My driveway is sloped I just always park it facing downhill.

[FISH4BUGS]

My ford 6.9 still has a minor issue that is caused by the same thing. If I park it on level ground no problems, Front end facing downhill no problems, Front end facing uphill. Very hard start. (longer it sits the worse) It is an air leak that is letting the fuel run back to the tank and creating an air bubble in the line. Sometimes you can troubleshoot these problems by simply parking it so the engine is lower than the fuel tank. if it starts right up then you know you have an air leak somehwhere.

I had a 1980 Mercedes 300CD that did exactly the same thing. Figured it out by trial and error. Small O-ring gasket in one of the injector lines was replaced and POOF! perfect starting again.

[Duckiller]

Fish4bugs you have doomed Phoenix to at least one day of chasing after the leaking O-ring. This will involve at least 4 trips to the parts house. Skinned knuckles, grease to his elbows, using words the may result in eternal damnation and the general waste of a day. His truck works, he just has to park it level or pointing downhill. Pointing out that it is a simple fix means he has to disconnect every fuel line joint to check the O-ring. This is a long time consuming job. Time could have been better spent casting boolits.

[rockrat]

I had a chevy suburban with the 6.2L. Never found the air leak. Ended up plumbing an electric fuel pump in the line in the engine compartment. When it started acting like air in the system, I would flip a switch, turning on the pump and things worked fine for a few days.

[JeffinNZ]

I think you guys may have nailed it. I will investigate at the weekend.

[FISH4BUGS]

Fish4bugs you have doomed Phoenix to at least one day of chasing after the leaking O-ring. This will involve at least 4 trips to the parts house. Skinned knuckles, grease to his elbows, using words the may result in eternal damnation and the general waste of a day. His truck works, he just has to park it level or pointing downhill. Pointing out that it is a simple fix means he has to disconnect every fuel line joint to check the O-ring. This is a long time consuming job. Time could have been better spent casting boolits.
Sorry Phoenix.....didn't mean to take away from your casting time.
Actually the repair is far simpler than that. Trace each fuel line visually. You WILL find a small leak of diesel fuel if a tiny leak is the problem. Pretty easy fix. My mechanic did it in about 15 minutes....but then again, he has been a factory trained diesel Mercedes mechanic for 35 years......
I have been driving mercedes diesels for 30 years. They all have certain mechanical characteristics that you learn over time. Fuel leaks and glow plus issues are always right up there....along with window motors and cruise control issues. Otherwise it is normal maintenance.....

[Phoenix]

installed the full injector seal kit no difference. I am pretty sure it is on the low pressure side of the injector pump. Something else I forgot to mention. It always starts right up (indicative of low side) then shuts off after a few seconds and wont start without 30 seconds of cranking. That pretty much guarantees low side. The fuel is running back into the tank due to an air leak in the low pressure line (that is why the tank being downhill is bad). Leaving the mechanical fuel pump to get fuel back to the inlet of the injector pump and an air bubble to get out. an electric fuel pump would lessen the pain, but not necessarily eliminate it.

[JeffinNZ]

Right, problem solved. There is a series of vacuum tubes that lead from the inlet manifold to somewhere else.... Now I can't pretend to know the exact role of said vacuum tubes BUT what I do know is they weren't doing much vacuuming as the tube terminations were perished. I trimmed back the ones I could and replaced those I couldn't and BINGO, warm starting instantaneous.

[Mal Paso]

Right, problem solved. There is a series of vacuum tubes that lead from the inlet manifold to somewhere else.... Now I can't pretend to know the exact role of said vacuum tubes BUT what I do know is they weren't doing much vacuuming as the tube terminations were perished. I trimmed back the ones I could and replaced those I couldn't and BINGO, warm starting instantaneous.

Vacuum tubes on a Diesel? Sounds like a Communist Plot.

I had a 6.9 International (Ford). Injector Pumps don't last and I always carried a spare. $500 with exchange if I remember. Got so I could change one on the side of a freeway in 20 minutes. Replaced it with a Dodge / Cummins and the problems went away.

[chsparkman]

Another vote for checking the battery and connections. A diesel takes a lot of power to turn over. When the engine is warm, and the glow plugs do not turn on automatically, the engine has to crank with authority in order for the compression to generate enough heat for combustion.

On an old suburban I had this very problem. I even went as far as connecting a Ford starter solenoid to an interior switch so that I could manually turn on the glow plugs when they wouldn't turn on automatically. This fixed my warm starting problems but later on I replaced one of the batteries and never had the problem again.

[a.squibload]

Good you got it Jeff, but I woulda bet a pint it was Coreolis effect...

[buckwheatpaul]

Check your glow plugs....depending on age ... they burn out and this will cause starting problems....easy to change ...cant remember how to test....google it....

[SourMashII]

If similar to the Ford/IH IDI, they are ground based, ohm their resistance.

GLow Plug theory is simple, (haven't played with diesel since I sold my IDI two years ago, bear with me), Basically they are a dead short to ground, and the "heat" is caused by running + to the hard - of the plug, thereby causing them to warm.

+ howevermany on the leaks, on the last IDI, I ran all new line tank to engine, and plummed an electric boost pump.

God bless the Schraeder valve....if it sat for aany period of time, it would bleed off... turn the key, depress the Schraeder til I got a stream of fuel, and voila! she'd fire faster than most gassers.