1991 chevy 1500 5.7 tbi erratic idle

[aggiedave98]

On a '89 burb, I had a problem with the engine dying. I replaced the iac, tps, and maybe something else since disconnecting one of them changed behavior and caused it to run. I was completely stumped. I also replaced the fuel regulator with no luck.

Then somebody told me it could be the fuel pump. Replaced it and bingo! Worked like a charm!

[NEUMANNZZ]

Originally Posted by tpulliam79

est bypass wire? is that the timing bypass wire?

yeah

[tpulliam79]

i will check and clean egr today and see how she runs with the timing wire unplugged today. also noticed I have to give it some gas to start it.( fuel pump maybe?) i will post back after i get the results.

[XLR8N]

you shouldn't have to give it gas to start a tbi motor. hmmm. sounds fishy

[tpulliam79]

Originally Posted by XLR8N

you shouldn't have to give it gas to start a tbi motor. hmmm. sounds fishy

thats what I thought so maybe fuel pump? not sure going to have the pressure tested either today or tomorrow,

oh and where is the fuel pump relay located on my 1991 1500 tbi 5.7. anything besides fuel pump that would cause me to have to give it gas to start?

[tpulliam79]

would the oil pressure switch have anything to do with idle?

[tpulliam79]

well it runs worse with timing wire unplugged, there is no vacuum to egr? there is vacuum on the other side of the vacuum solenoid . should there be vacuum at egr while running? and if so would this cause a surging idle?

[NEUMANNZZ]

I would check fuel pressure(9-13psi) if its running worse with est wire disconnected. that means the egr selenoid is closed. I assume there was no change when you disconnected the vacuum line going to the egr. looks like the egr system is working.

[NEUMANNZZ]

If the egr selenoid was open then you would have a rough idle and driveability problem.

[tpulliam79]

going back to my friends shop tomorrow to test fuel pressure and relay. would the relay be the reason why I have to give it gas to start it?

[NEUMANNZZ]

no.

[XLR8N]

Originally Posted by tpulliam79

going back to my friends shop tomorrow to test fuel pressure and relay. would the relay be the reason why I have to give it gas to start it?

i have never heard of a relay "going out" i have always just seen it go out once and it is done. but if you are infornt of your truck looking at your engine bay you will look to the left of the dizzy and on the fire wall you should see a black "shroud" there is three plastic nuts you take off and then take the shroud off and you will see the relay there.

[XLR8N]

i also dont think a fuel pump going out would make you have to push the gas to start it. unless it isnt pushing enough full through the lines. your injectors are working correctly?

[tpulliam79]

the injectors seem to be spraying well, if the fuel pressure is right then I guess the next logical step would be new injectors and rebuild of the injector pump and new fpr.. but I will wait and see what my tech says tomorrow. hopefully we can figure it out. oh and my truck will start without me pushing on the gas it just takes about 5-6 seconds of cranking?

[XLR8N]

so you will push the pedal and crank the engine and it will start right up? and if you do not push the pedal it will take 5-6 cranks?

[tpulliam79]

Originally Posted by XLR8N

so you will push the pedal and crank the engine and it will start right up? and if you do not push the pedal it will take 5-6 cranks?

yeah with gas pushed starts right up without takes some time.

[tpulliam79]

Originally Posted by XLR8N

so you will push the pedal and crank the engine and it will start right up? and if you do not push the pedal it will take 5-6 cranks?

does this point towards something? also the short block is from a 78 blazer and the heads are from the 91 so it would stay tbi, would this cause any differences?
the truck also sounds as if the fans in the dash are always on except when I turn or accelerate but then the sound come right back, no air out of vents but sounds like a small fan in the dash is always going except for when I accelerate or turn?

[XLR8N]

as far as block and heads different years that is fine it wouldnt be the problem. so did you check your FP?

[tpulliam79]

gotta take my son to school at 9:40 then im off to my mechanics shop... will post results when I get home. any clue on the noise from the dash?

[hornsfan10609]

I bet you need a new fuel pump, they go out in almost every truck and usually don't last as long as yours already has. Only go with AC Delco for fuel pumps, unless you want to be replacing it all the time, do it once and do it right.