92 chevy 4.3 rough start

[chevy92]

1992 blazer 4.3 2wd; when the truck sits over night or for just a few hours i have to crank it for awhile to start and i all most have to force it to start. But when the truck sits for about ten minutes it starts right up. Also when im stopped the truck surges after about 1min of being stopped. so far i replaced plugs,cap rotor, i just put high flow cat and exhaust, also clean egr valve and fuel filter. someone please help!!!!! im lost

[myndkrime]

Have you tested your fuel pressure?

[Tha_Boom]

Sounds like your idle air vavle is dirty or bad. it screws into the pass side of your tbi.

[chevy92]

i have not tried the fuel pressure but someone told me that if its a little off the truck runs like sh--t. bhut i will start with both ideas thanks

[BlazerLT]

IAC valve is only in operation when the truck is running and maintains the idle so that won't be your problem.

Sounds like you have a bad check valve letting fuel go back into the tank instead of maintaining a prime right at the engine.

That or you have a poor CPI unit if you have a CPI engine.

[chevy92]

where would i look for the check valve.

[BlazerLT]

sending unit

[Tha_Boom]

Quote: Originally Posted by BlazerLT

IAC valve is only in operation when the truck is running and maintains the idle so that won't be your problem.

Sounds like you have a bad check valve letting fuel go back into the tank instead of maintaining a prime right at the engine.

That or you have a poor CPI unit if you have a CPI engine.

Uhm IAC IS in operation while the truck is starting otherwise you would have a choke and you would have to push the gas to get it to start.

[BlazerLT]

Direct quote from shop manual:

"The Idle Air Control valve controls engine idle speed. The IAC motor reacts to voltage pulses from the ECM to move the pintle a given distance in and out for each pulse. The is movement controls air flow around the throttle plate, in turn determining engine idle speed while the engine is in operation."

I myself have had to replace a defective IAC valve which didn't affect the starting whatsoever. All it did was cause and erratic and unstable idle that sometimes would lock out at 1200rpm.

What acts like an electronic choke for the 4.3L is the coolant temperature sensor which when reading a cold coolant temperature, richens up the fuel mixture while the coolant is cold. When it warm up, it sends a signal to the computer to lean out the mixture for normal operation.

What this gentleman is having is a fuel problem where his fuel pressure bleeds off due to a fuel line leak or a defective check valve allowing the fuel to bleed back into the tank. This in turn causes the several seconds of cranking to regain the lost fuel pressure in the main line.