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Guest Message by DevFuse

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1989 GMC van, TBI, stumbles at part throttle

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#1 MilesFox


    Catch this Fox!

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  • Madison/Milwaukee, WI

Posted 12 May 2012 - 06:38 AM

I have a free van from a retired painter. This van is a 1989 gmc/chevy '20' panel van 305 v8 automatic TBI.

this thing has only 88,000 mi, but has sat for the better part of 10 years.

Since we had it, the crack heads chopped out the cats, and now it has a cherry bomb and side pipe. She runs great on the highway, but at part throttle acceleration, especially on hills, she stumbles and backfires thru the TBI. I have to feather the pedal, or completely bury it to get her to move.

There is a lot of vacuum sucking noise, but i cannot find a leak or loose fitting. There is a broken nipple on what appears to be an EGR control solenoiid. This van has electronic ignition and coil packs. She has some original looking delco or autolite spark plugs.

I am wondering if the timing is off? it drives as if the vacuum advance isn't working, but it is load sensitive, and an electronic disty.

I am not familiar with these archaic american v8's as they are as foreign to me as a subaru engine is to any old-timer.

the van seems to run right until it is warmed up, although it idles a bit higher than it should. IT drives like it has a vacuum leak.

So, what is the GM TBI system sensitive to?

is there some kind of thermo vacuum switch that fails?

can an engine temp sensor throw it off, and where is it located.

there is an oxygen sensor present, as i have located it on the driver side manifold.

what are common problems and common fixes for this type of generic engine?

there is an oil leak on the back of the intake. that will be fun to fix. I want to smack the general for using a 30 year old engine in 1989. Wouldn't you smack FUJI if they were still slangin' ea82's in the '12 wrx?

#2 Subruise


    Official Party Pooper

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  • pierce county

Posted 13 May 2012 - 01:46 PM

my old boss had one of those. make sure theres no cracks in stuff like the disty/cap. timing could be off and, iirc vacuum was kinda a pita on that thing. we did a bunch of work on it and it was still gutless. 305s, pfft. is your tbi/electrocarb doin its job?

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