Car won't start when engine is warm

[richierichness]

Rb25 s2

Are my coils bad?
Just upgraded my fuel rail and injectors. Car starts up and idles fine. However once the car warms up it starts to idle a little rough and shuts off. Can't start the car again till engine cools.

I thought maybe it was the spark plugs so I replaced them. Also put a new battery in the car for good measure. Been tuning the car with Elite 2500. Using MAP based VE logic.

Any help would be appreciated


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[Kingtal0n]

sounds like it needs tuning. when it warms up the IAT and CTS take or add fuel, you check the percentages in the software and you can zero them out for diagnosis purposes, or fix them so there is less or more as necessary.

Rough idle, then shutting off, sounds like its leaning out. the iat might be heat soaking and rising rapidly to portions of modifier where its taking massive amount of fuel out. You should be watching the wideband to confirm diagnosis. Dont tell me you don't have a wideband on a car with a standalone...

[richierichness]

sounds like it needs tuning. when it warms up the IAT and CTS take or add fuel, you check the percentages in the software and you can zero them out for diagnosis purposes, or fix them so there is less or more as necessary.

Rough idle, then shutting off, sounds like its leaning out. the iat might be heat soaking and rising rapidly to portions of modifier where its taking massive amount of fuel out. You should be watching the wideband to confirm diagnosis. Dont tell me you don't have a wideband on a car with a standalone...

I'm running the Haltech WB02. There is no leaning at idle. Fuel trims are within 2-3% of target. IAT theory i'll look into but doubt it has anything to do with my issue since I never made changes to my map...only changes have been fuel related.

[dbeiler]

Worn coils will have a constant misfire. If they're worn (the insulation cracks and spark jumps to head instead of being routed through the plug) it'll be noticeable immediately upon startup; especially on rainy/humid days.

Any heat soak engine performance issues are usually caused by failing, heat sensitive electronics. Camshaft and crankshaft position sensors are the primary suspect.

My go-to trick is to run the engine till it heat soaks and begins running poorly, shut it off, remove the suspect component (the CAS, in this case) and pop it in the freezer for a few minutes to cool it off. Reinstall the component onto the still heat soaked engine and fire it up. If it now runs correctly for a few minutes; you've found the problem.

I'm assuming you've monitored the battery voltage and air/fuel ratio to eliminate any concerns in those specific areas.

I keep telling people: these engines are now twenty years old. If it's still on the original coils and CAS and they haven't failed yet, they are guaranteed to fail in the near future.

[Kingtal0n]

Are you sure the wideband is correct. if the engine has fuel and doesn't seem to misfire there is no reason for it to quit running, unless the compression was failing.

Do you know how widebands are supposed to work? Have you ever had one before? Is this your first wideband? If you've never tuned a car on a wideband before, my bet is the wideband isn't working and you are being fooled.

Not making fun of you; I've come to plenty of cars whos owners were telling me over and over that there was plenty of fuel, why doesn't it run? I get in the car and the wideband is dead as can be, the owners had no clue. They don't tune the car so they didn't know I guess. It would just sit there at some number 14:1 or something. It isn't supposed to do that; they respond fairly rapidly to changing conditions and jump around quite a bit. You should be able to reduce fueling and see the wideband report the change dramatically as the engine begins to choke from lack of fuel.

[richierichness]

Thanks for all the input. It looks like two issues. The first problem is that my idle still is a little rough and sometimes causes the car to shut off once the engine is hot.

Second issue is solved. The car wouldn't start when hot because of a cranking fuel table not being rich enough. Idle fueling is fine. Obviously can't really monitor fuel while cranking the engine.


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