Truck Floods When Starting Warm Engine

[ImpetuousNinja]

Hello Everybody:

I have a problem with my 1996 Chevrolet Silverado (5.7L). The engine starts no problem when it's cold, but after warm up the engine floods. At least I assume it's flooding because if I depress the throttle pedal while cranking, the engine starts. It then revs up to about 2000 rpm before settling back down to normal idle speed. The truck seems to run fine after starting and operates normally.

I did some research and someone suggested it might be the Idle Air Control stuck in the closed position. I didn't think this was the problem since the engine runs normally once started, but I took it off and checked it just to be certain. The valve seems to be operating normally so I reinstalled it.

Another idea was that the Fuel Pressure Regulator might have a hole in the diaphragm which allows gas to leak into the engine. The FPL costs about $73 and is located under the intake manifold plenum (black piece covering the manifold).

I wanted to see if anybody here thinks this is the problem or if there is something else I should check before I spend the money and time tearing off the top of my engine.

[MrShorty]

FPR is usually best checked with a fuel pressure gauge. In this case, you're looking to see if the fuel system can hold pressure after the fuel pump shuts off. I've also seen reports that, when the FPR is leaking in that fashion, you can see a "clean" spot/trickle on the inside of the intake by looking down through the throttle body where the gasoline has cleaned off the carbon.

[ImpetuousNinja]

FPR is usually best checked with a fuel pressure gauge. In this case, you're looking to see if the fuel system can hold pressure after the fuel pump shuts off. I've also seen reports that, when the FPR is leaking in that fashion, you can see a "clean" spot/trickle on the inside of the intake by looking down through the throttle body where the gasoline has cleaned off the carbon.

Thanks for the information MrShorty--your response is greatly appreciated. I will check it out tomorrow.

I did notice something new since I posted. I took the truck out for a drive and it keeps accelerating even with my foot off the throttle. I started from a dead stop and simply released the brakes. The truck gradually accelerated to 35mph before I finally started riding the brake so as not to exceed the speed limit. It does this regardless of the engine being cold or warm.

The engine seems to idle normally (no excessive RPMs), and doesn't 'rev up' while driving at low speeds. I actually noticed this the other day, but thought that it was my imagination so I forgot about it until today.

It seems I have a problem with getting too much fuel at startup & during low speeds. Also, I get no warning lights on the instrument panel. This really has me stumped.

[GaryL]

I did an FPR on a 96 with a 5.0 litrer a few months ago. His was idling rough and getting lousy gas milage. I put the new one on and the problems went away.

[ImpetuousNinja]

I thought I'd update this post in case it helps anybody else.

I was going to test the FPR as suggested by MrShorty, but I got to thinking. (I know--sometimes that can be dangerous!) The problems I was having were related to temperature, so I decided to test the engine coolant temperature sensor.

I found some information regarding a test procedure that didn't require pulling the sensor from the engine. I removed the electrical connector on the sensor and noticed that one of the pins on the sensor was very rusty. I also noticed that the receptical in which the pin resides inside the connector was rusty. I used some electric motor cleaner and a small brush on a Dremel to clean the pin and the pin receptical.

I then gave both a shot of WD40 and blew them out with compressed air. I let them dry for awhile and then plugged the connector back into the sensor. I took the truck out for a test drive, and bingo--no more problem!