Chevy & GMC Vans

Post subject: Re: major headache Reply with quote
Bill's right, try blocking off the EGR with a plate. You have nothing but a gasket to lose...

did that , no change .

I can't read all this again but have a couple of things to add that may not have been mentioned. Seems you said you had good spark,,what did you do to know that ? The reason I ask is, if you pulled a wire and could see the spark, this doesn't mean you have the amount of fire you should have. Question is,,how much spark do you have at the plug, not wire to plug ?
If this isn't it, I still say it's in the dist. Don't know how the 4.3 dist. are made but know on the old HEI's the base can actually turn on the shaft if the press fitting becomes loose. When you speed up the base will turn and throw the timing all out of wack. Check the dist parts again,,not the electrical parts but the parts that make up the bare dist.

Are there new plugs installed and if so, have you flooded it after you put new plugs in ?

Also ran in to the same issue when my son and I swapped a larger intake on his Camry. Idle would go way up, then drop back down over and over,,,this was an O2 sensor causing this on his Toy.

if it was bad spark it would not start and keep running if you feathered the gas peddle . firing order has been checked dizzys been checked over by at least 2 good mechanics . all plugs ,wires have been replaced . its not flooding itself out . for external componants on the 4.3 we have 2 of just about everything , with exception to things that are not interchangable like the TPS just about everything from my 88 is the exact same parts that are on his 92 & we still have all those parts , they have all been swaped or replaced with new or known good parts .

i'm leaning towards a vaccum leak we can't track down or a faulty TBI .his original TBI was replaced but who knows if was a good one or not .

if anybody has a TBI unit , intact please, they want to donate or sell fairly cheap ,please let me know . i would prefer one that was pulled & working when pulled . its gotta be from a 91 to 93 cuz the earlier ones are different & so are the later ones . little changes like hose connections & different TPS units but changes never the less .

skippy wrote:

Post subject: Re: major headache Reply with quote
Bill's right, try blocking off the EGR with a plate. You have nothing but a gasket to lose...

did that , no change .

Come to think of it, that was a stoopid idea. What the heck was Bill thinking?

there are no stoopid ideas ,just need one that will get this pig up & running again !!!!

If it's a vacuum leak something must have a small crack somewhere. There's a long hose back to the gas tank, have you checked that one all the way back?
on another note, with an HEI system, the spark from the coil wire to the dist cap should jump a gap almost 3/4" when tested. If it doesn't, the voltage from the coil is lower than it should be. I've been chasing a not start, stall at highway speed issue on one of my jeeps, this is one of the kernels of info i ran across in my research.

The only other thing I've seen like this that was so hard to diagnose was a pulsator between the fuel pump and the fuel line in the gas tank. I doubt that with a tbi system you have a pulsator,, but a pinhole in the rubber tube between the pump and fuel feed line will cause the same problem. man I am runnin out of ideas. bad valve maybe?

petey, Bill was trying to help

The spark is fine guys , i get a good hot spark at better than a 1" gap . just short of going over gthis thing with a magnifying glass , i don't know what to do next .

Did you say you checked the tps???Or do you think its the whole TBI unit?

TPS has been replaced & checked , IAC was replaced &set to factory specs & adjusted hoping it would make a difference , FPR was replaced with new , throttle body was replaced with a used one & rebuilt & all listed parts put in it . but who knows , i'm trying anything at this point .

i'mthinking worn throttle plates now ,hoping another tbi might help

Sooo,Skippy your saying it starts off starting fluid??.

No gary , its starts just fine , just won't stay running .

Hows the terminal on the oil pressure switch? is it corroded or loose,broken off? just a stab in the dark.

Sorry Skippy.This thread has gotten so long it is hard to keep tract.So you checked the fuel pressure as it is running??.Could it be the pump can't keep up??.

Try to think why feathering the throttle helps keep it running- does it die because it is lean or rich ? by feathering the throttle are you giving it more air , more fuel , both ?

I suspect there is something going on with the TPS - is there a pedal position sensor ? or just the TPS ?

If teh TOS needs to be moving to keep it running, that could mean that the idle signal isnt getting through , or the TPS is in the wrong position or you have the wrong TPS on the van

Follow the wires from the TPS and check all the connections- it could be just feathering the throttle is wiggling a wire somewhere.

oil pressure switch is fine ,fuel pressure is in good parameters , The TPS was replaced & checked for proper operation with my meter .