91 Lumina - Engine doesn't start right up - have to hold gas down to get it to run

[foolishamber]

I have a 91 Lumina, 3.1 L. Sometimes, in order to get the car to stay running, I have to hold the gas down. Other times I have to turn the car on and off about 5 times to keep it running. Then there are times when it will start and run just fine. Things that have been replaced include : map sensor, throttle position sensor, idle motor, coolant temperature sensor, spark plugs, fuel rail with injectors, and ignition control module (coil packs). I'm thinking it might be the crankshaft position sensor - is this a possibility, otherwise what else could it be?

[tblake]

that sort of symptom doesnt sound like a bad cps. To me it doesnt even sound ignition related. Sounds to me like the fuel system isnt holding enough pressure. If you have a fual pressure guage, hook it up, and turn the key to on. It should pump up the pressure to 40psi I believe, and it should not bleed off. If it pumps off and bleeds off quickly, pinch off the fuel return line and try it again. If the pressure stays, you have a defective fuel pressure regulator. If pinching it off does nothing, and it still bleeds off quickly, then there is probably a bad check valve in your fuel pump. But first things first, how long has it been since you have replaced your fuel filter? If its been a while, or never, may want to change that. If nothing I suggested works, look deeper into the fuel system. Crank position sensors will be good until they get warm and then they fail, but your problem is when the car is cool, and once its started will run. correct? The fuel delivery system is more than likely where your problem is.

[tblake]

Not wanting to idle on its own could also be caused by a vacuum leak. Check all the vacuum lines, and make sure they are all connected, and not cracked or frayed apart at the ends.

[the6]

Originally Posted by foolishamber

I have a 91 Lumina, 3.1 L. Sometimes, in order to get the car to stay running, I have to hold the gas down. Other times I have to turn the car on and off about 5 times to keep it running. Then there are times when it will start and run just fine. Things that have been replaced include : map sensor, throttle position sensor, idle motor, coolant temperature sensor, spark plugs, fuel rail with injectors, and ignition control module (coil packs). I'm thinking it might be the crankshaft position sensor - is this a possibility, otherwise what else could it be?

if you have 3 wires on your oil sending unit short out the 2 across from each other. at the plug with a paper clip. fuel pump won't come on if the oil pressure is low.