Help! Car starts hard when engine is warm

[BrianZ]

I have a 1992 corvette LT1 with 58000 miles. The car starts hard when the engine is warm. What I mean by "starts hard" is that the engine cranks over just fine but it cranks over for about 3 or 4 seconds before it starts. If I've driven the car and then shut it off and wait between about 45 minutes to 2 hours it starts hard. After it starts and you drive it, it will sputter when you push the gas pedal down about half way. After driving it a mile or so it clears out and runs fine. It starts and runs fine when the engine is cold. I've checked the fuel pressure regulator and no fuel is coming out the vacuum port on it. I attached a fuel pressure gauge to it and ran the engine until it was warmed up and shut it off. The fuel pressure stayed at about 40 P.S.I for about 2 hours. So I know the injectors are not leaking. I replaced the coolant temp. sensor. Cleaned the throttle body. Had pressure building up in the gas tank so I replaced the vapor canister, vapor canister purge valve and the vapor canister purge solenoid and that fixed the pressure in the tank problem but it still starts hard when the engine is warm. I don't get any faults and the check engine light never comes on. Any ideas? I plan on replacing the fuel filter this weekend and the spark plugs in the near future but I don't see how either of those could cause this problem.

 

[Schrade]

Welcome onto the boards there...

Looks like you read my reply to the 'hot start' thread, just below yours... I don't know what to tell ya there.

Gaseous pressure in the fuel tank is normal.

Any loping idle when warm? How DOES it idle warm?

 

[BrianZ]

Schrade, it idles just fine when the engine is warm. However, if I start it when the engine is warm and it starts hard it will idle a bit rough but then returns to normal after I drive it for a mile or so.

Big Jim, I've checked the fuel pressure. Had a fuel pressure gauge connected to it, ran the engine until it was at normal temp. and shut it off. The fuel pressure stayed at about 40 p.s.i. for about 2 hours. I've also taken both fuel rails out immediately after shutting off the car. I can have the fuel rails out in under 10 minutes. Still not fuel leaking from the injectors.

 

[96gs917]

Brian,

Welcome to the forum. Sounds like your fuel system is fine. Was the Opti every replaced?
Since you are not getting any codes, could be that, especially since you are discribing a hard start,
sputtering condition.

I'm sure the experts will chime in soon with some additional info.

 

[BrianZ]

I haven't replaced the optispark distributor yet and not sure if it has ever been done. That's one of the things I've considered as causing the problem. I figured I'd do the easy stuff first as I believe you have to remove the water pump and harmonic balance to replace that. Can you replace it like a regular distributor cap and rotor? Or do you have to replace the entire unit?

 

[96gs917]

Corvette Action Center | Tech Center | C4 Corvette Tech Center | C4 Corvette Optispark Dissection and Replacement

Here is a link describing the Optispark. I do not believe you can just replace the cap and rotor. It's all one unit.

I think the strategy you describe is a good one. Keep going.

 

[Schrade]

Schrade, it idles just fine when the engine is warm. However, if I start it when the engine is warm and it starts hard it will idle a bit rough but then returns to normal after I drive it for a mile or so.

Big Jim, I've checked the fuel pressure. Had a fuel pressure gauge connected to it, ran the engine until it was at normal temp. and shut it off. The fuel pressure stayed at about 40 p.s.i. for about 2 hours. I've also taken both fuel rails out immediately after shutting off the car. I can have the fuel rails out in under 10 minutes. Still not fuel leaking from the injectors.

So then DON'T drive it to get it to normal when it's a this 'bit rough' point. This is when you can catch the culprit with a scanner with data logged, and posted here. This is what I was asking about idle quality.

Does this replicate EVERY time???