No start condition after driving

I have a 1990 Toyota Celica, and I’ve been having trouble with it not starting after driving. There are no symptoms when the car is running, aside from a very slight rough idle. The car starts fine after sitting for 3-4 hours, but for short trips where it’s off for under 1-2 hours, it cranks but will not start. The cranking also seems weak unless I floor the gas while trying to start, and sometimes it will eventually start if I hold the gas while cranking. It always starts at the beginning of the day.

This leads me to believe I’m dealing with a flooded engine, but I’m not sure how to diagnose why. I thought it might be leaky fuel injectors, but wouldn’t that cause symptoms when running?

Perhaps your fuel pressure regulator has a ruptured diaphram causing gasoline to leak into the vacuum line. I had the same problem with my 92 Buick.

Thanks! Any idea on how to test that? And would the car be able to run fine once started if it has a ruptured diaphragm?

The way to test it is to remove the vacuum line from the pressure regulator. Do it after running the engine. You should NOT see any fuel coming out of the narrow vacuum pipe attached to the regulator. If you need a new fuel pressure regulator, get it replaced pronto. A defective regulator could create maximum fuel pressure to the injectors and be a possible fire hazard.

Thanks! I tried that, but no gas came out. Does that mean I should be expecting a leaky injector?

It does sound like a rich mixture on hot starts. I have an early 90’s Corolla, and on that car anyway a cold start injector is used. It injects extra gas when the engine is cold. There’s a thermal timer which screws into the cooling jacket that controls how much extra gas is injected. On hot starts it shouldn’t inject any extra gas at all. Otherwise you’d get a rich mixture and hard hot starts. So maybe something is wrong with all that. It’s usually fairly easy to remove the thermal timer and bench check it. Maybe ask your mechanic to do that, provided the Celica uses this same mechanism. I’d do this before considering a leaky fuel injector.

Ok, I’ll definitely look into that. My car will start within 5 or 10 minutes of turning off; it seems to be the 30 minute - 2 hour range that’s troublesome. Could that thermal timer be messing up only at certain temperatures as the engine cools?

Possibly. It’s a heated electrical switch screwed into the coolant jacket, shaped sort of like half a cigar, heated by the coolant and by its own internal resistors. A lot of possible failure modes. The switch on the inside of this gadget could be sticking, not opening or closing at the appropriate time. One or both of the internal resistors could be burned out. etc. It could be the cold start injector too, but less likely. There are numerous possibilities beyond the cold start valve/thermal timer too. Injectors. Ignition system. Fuel pump or check valve. EGR sticking, internal engine damage, etc. But checking the thermal timer is pretty easy and as your symptom is consistent with a thermal timer failure, I think it makes sense to eliminate that before moving on to something more difficult to check. The weak cranking is probably a different problem. But it wouldn’t hurt to get that looked at too. Possibly might be related in a non-obvious way. Best of luck.