Hot start problem

Hello,

1999 Grand Prix SE 3.1 litre 206000 miles.

My car does not start well after sitting hot for about 30 minutes. It will fire up,run for a short time, bog down and die. It is like the engine is getting flooded.

If I release the pressure through the Schrader valve and try to restart it will run, otherwise I need to wait about an hour and it will start, stutter, and finally run OK.

I have been having this issue for several months, and it is getting worse. Today I tested my fuel pressure and I found it increased by 12 psi within 30 minutes of shutting the car off. I thought a slight dropoff would be normal, but I did not expect the pressure to rise by that much. I am also not sure how good the gauge I used was ( borrowed from autozone ) and my readings seem low. The car runs perfectly after a cold startup, but my fuel pressure rose from 25 psi to 37, which is below normal I think. Could the fuel pressure regulator cause this? There is no gas leaking out of it. There are no trouble codes and the SES light is off.

Thanks in advance for any ideas.

Normal pressure for this car is around 40 psi....if your pressure is 25, that is too low....to see what your max fuel pressure is, turn key to on(don't crank), then off for 5 seconds, then on, then off for 5 seconds, then on, until you get max pressure....then see if it holds at that pressure.....

On a hot engine, I can see the fuel pressure rising easily over a period of time....

Sounds like your car is running rich.......I assume that fuel pressure is holding, since it is rising.....air filter ok? my first thought was a leaking regulator, but you found no gas in the vac line....

Another possibility is the ECT sensor...if your vehicle thinks the vehicle is running cooler than it actually is, it will cause it to run rich....

You have checked for codes and there are none...

One thing to try is slightly step on the gas pedal, and then crank when warm....if it starts, you may have to clean that throttle body....

Also, last time this vehicle had a complete tuneup?

Thanks for the fast reply

My air filter was changed not long ago and looks ok but I will replace.

I replaced the spark plugs last week and they all came out a greenish white color..no cylinder was any richer than the other. I replaced the wires also, and I have tested all 3 coil packs.

I changed the coolant temp sensor yesterday, and now my temp gauge reads 40-50 degrees higher than it did before. This has not solved the problem.

Pressing on the gas pedal has no effect other than making it worse..since this problem started I have changed the plugs, wires. cleaned the MAF, tested the car with the MAF unplugged, changed the MAP sensor, and checked for any vacuum leaks. I read on another post that this could be caused by a leaky injector...still if the car starts it should continue to run once the extra fuel is burned up right? I am going to change the regulator tomorrow and I will post back. Thanks again.

Today I changed out the regulator and cleaned the throttle body. The problem has not gone away. I have never changed the fuel filter on this car and it looks like it could be original. Don't know if that could cause a problem like this but it should probably be done anyway. My fuel pump does not sound loud and when the car does run it is perfect without any hesitation at all.

Thanks to all who have viewed this thread and to Tech II for your reply. When I finally figure this out I will post the solution so that it will hopefully be of help to someone in the future.

Hello again,

Today I changed the fuel pump with an aftermarket replacement from Rock auto. To my surprise, when I pulled the old pump it was an identical, aftermarket pump. I have been driving this car since 2008 with no trouble like this until recently. The pump seated OK thanks to the helpful guidance I got from reading old posts on this forum. I had an issue with one of the quick connectors leaking, but after some frustration that is also resolved. I will be checking this closely for the next several days at least to be sure there are no leaks anywhere in the system. So far, the O ring is not leaking and the snapring area is completely dry. I have about a half tank right now.

Tech II was right, my fuel pressure was too low. The car starts perfectly now, cold or hot, and seems to run a little better too. I guess the moral of this nightmare is that a weak fuel pump can sometimes cause a hard start condition only when the vehicle is hot.

Change that fuel filter.....

Already done...Thanks!