Warm Start Issue

[SourceLee]

Cold starts, perfect! Hot starts, beautiful. Warm starts, no start. It's behaved like this since day one (5 years ago). 1992 Fox Body 5.0 "comb over" EFI. TrickFlow stage 2 top end kit. Tune and chip. Local speed shop couldn't figure out why it doesn't like to start when it's lukewarm. Their solution: Make sure it's completely "up to temperature" before you leave the driveway. So, I do. Right up until the point where I don't. Then I'm reminded the engine doesn't like to restart when only partially warm. If I let the car sit for an additional 15 -20 min, it'll start but not a crisp start. This condition existed both before and after the tune and chip. New fuel pump, new high flow fuel filter, fairly new plugs, new wires. Any ideas what's going on?

[Railroad]

Just a guess,,,, fuel injectors leaking into cylinders, flooding engine. A hot engine can cook off the excess fuel, but the less than hot engine is flooded,,, cold engine needs to be richer to start and injectors may not be leaking until they get hot.
Good luck,

[kgkeys]

Check your fuel pressure regulator, too. They're vacuum operated and if the diaphragm is torn, they can let fuel suck into to the crankcase richening the mixture. Like Railroad said, a hot engine can burn it off, after a while it cools down, the excess fuel evaporates off and a cold start is fine. Check your oil and make sure it doesn't smell like gas!

Kyle

[Hellion]

I ran into a similar issue with my setup, except it was usually hot starts that I had a starting issue with not lukewarm. After a drive, it would sit for about 10 minutes or so and would have trouble starting. However, if I would restart in about 5 minutes or less - no problem. To get her started, I'd let her sit for 20 minutes and she would start but not clean. What solved the problem was checking/performing the basics:

1. Check/clean mass air sensor and check/clean/replace air filter.
2. Check/set base timing.
3. Perform idle reset procedure, including resetting the throttle position sensor (TPS) to .98 and testing idle air control (IAC) valve.
4. Ensuring fuel pressure is at 40 psi and changing fuel filter.
5. Checking for spark when car doesn't start.
6. Check/replace cap, rotor, spark plugs and wires.

I'm not saying you'll need to do all of these, since I replaced most of my components and performed these items. I believe my issue was caused by a dirty mass air sensor in addition to the idle not set correctly. In addition, it may clearly be something else, such as a leaking fuel injector as mentioned above. The previous owner relied on a speed shop to do everything and the car was really messed up when I got it (for a great price I might add). I've got her just about dialed in now, so I hope this helps.

[Railroad]

Just another WAG. Check your battery and alternator. If your battery is questionable, initial start current used, may not be restored until the engine has run long enough to reach full temp. Hope that makes some kind of sense.
5 years ago, you may still be on the same battery and probably the alternator too.
You could jumper a second battery on, as a test.

[michael everson]

I had a similar issue with a customers car. By accident we found that if we didn't let the fuel pump prime the engine, it would start. We would trip the safety switch and then crank the engine. Just as it was about to fire we pushed the switch in and it would start. We traced it to a bad ECU. Replaced the ECU and it never happened again. We think it was somehow flooding the engine when hot. Sent the old ECU to be fixed but the could not find anything wrong. I tried it in another car and it did the same thing.
Mike

[SourceLee]

Fantastic guidance everyone. I'll try all the above starting with the least expensive and then working my way up from there. With the above suggestions I'm convinced this issue will be solved in short order. Thanks everyone.