Hard start when hot

[DoctorDex]

Originally Posted by Blue94VR4

This is quite common and in most cases caused by fuel control solenoid on the firewall. When engine is hot solenoid applies atmosphere pressure (instead of vacuum) to the pressure regulator. The idea is to make car run richer first couple of minutes. To test this theory in your case connect fuel pressure regulator to plenum directly and see if it help. It's a part of vacuum reduction mod.

If anything, I found the solenoid actually helped my hard start when hot problem. When I'd start my car "hot" my car would want to run lean because of what I believe is vapor lock in the lines. Reinstalling the solenoid didn't cure the problem completely, but my car starts fine, runs a little lean (15.5 - 16) for 20-30 and then goes to stoich. Without the solenoid it'd "chug" for 1-2 minutes (with AFR's of 17-18) before going to stoich.

[DoctorDex]

Strange thing I noticed the other day. I was driving my car "hard" for ~ 30 min and then I had to stop at the store for a few minutes. My car has a turbo timer so it idled for 2 - 3 min before shutting off. When I came out of the store ~ 20 minutes later, my car started easily, but it was running on the lean side (16.8 - 17 ish) and for the first few seconds I could hear what I can only describes as sort of a whirring/rustling sound coming from the rear. The only explanation I can come up with is maybe the noise is caused by the depressurization of gas vapors when they are entering the tank via the return line. Anybody else noticed this or does anybody have a better explanation?

[DoctorDex]

Back from the dead.

It has been very hot out over the past few weeks and I've come to the conclusion that my hot start problem is definitely _not_ cured.

I've tried disconnecting the FP solenoid --> seems to be even worse.
I've tried running the fuel pump using the check connector to get a rid of any possible source of vapor look and the prime the fuel lines before starting the car --> car starts right away but then it wants to run extremely lean for the first few minutes. If I try and rev it up I can't get it above 2600 rpm.

I'm curious if the "lean" condition is caused by missing (ie. spark plug not firing), which is spilling O2 into the exhaust causing it to look lean?

[TURBOSareCRACK]

i'm having the same problem, did any of this happen after you modded or touched anything in your car? Ever since i modded mine it started doing this, i'm going to try and find out whats wrong with it this weekend.

[DoctorDex]

Noticed that my FP solenoid isn't doing what it is supposed to, ie. it isn't increasing FP to base (atmospheric) pressure. Been thinking about this problem for a bit and I realized this problem might stem from the fact I'm running a MAFTranslator feeding a fixed temp. and baro signal to the ECU?

The only thing is that this doesn't explain why people with a stock intake system also have this problem. Does anybody know which temp signal the ECU uses to determine hot start conditions? Is it the coolant temp signal or is it the air temp signal?

[braddman]

I also have this problem and I smell fuel as well after it. After reading through the thread I'm still not sure what to try next.

[mako]

Are you sure you don’t have dirty injectors. What can happen is the injectors stay open (due to dirt) after you shut the car off and this causes the cylinder(s) to load up with fuel. If you smell fuel after you start, that could be your problem. Try putting the pedal to the floor to see if it starts “somewhat easier”. You may want to try and put some Techron in the tank to clean the injectors.
Mako

[braddman]

Originally Posted by mako

Are you sure you don’t have dirty injectors. What can happen is the injectors stay open (due to dirt) after you shut the car off and this causes the cylinder(s) to load up with fuel. If you smell fuel after you start, that could be your problem. Try putting the pedal to the floor to see if it starts “somewhat easier”. You may want to try and put some Techron in the tank to clean the injectors.
Mako

Why would dirt only do that when warm? It's only hard to start when warm.

[mako]

In a flooded situation (like an injector(s) leaking into cylinder(s), putting the pedal to the medal until it starts clears a flooded engine faster due to more air getting into the cylinders and drying it out faster. Then you get a gas smell out the exhaust once started.
If this sounds like it’s it, Techron in the tank a few times.
Mako

[braddman]

Originally Posted by mako

In a flooded situation (like an injector(s) leaking into cylinder(s), putting the pedal to the medal until it starts clears a flooded engine faster due to more air getting into the cylinders and drying it out faster. Then you get a gas smell out the exhaust once started.
If this sounds like it’s it, Techron in the tank a few times.
Mako

I see what you're saying, but what I mean is why would it be flooded only when warm. Is it just because when it's cold most of the fuel left over from the last time it was running has evaporated?