trying to fix Jr's truck as it doesnt want to run right... when the we got it, it ran perfect. Sat for a month or so then fired it up and it ran like crap. took it fora spin and it acted just like a bad fuel pump, surging as if it was starving for fuel. So here's what we've done to it...

new fuel filter,

checked fuel pressure under load...( in gear with some throttle) sits at 12.5 psi, range is 9-13psi.

take a peek at the injectors and the appear to be working.

checked all the vacuum lines for leaks, none.

then I went to set the timing and yank the connector that i'm instructed to and fire it back up and it purrs like a kitten, idles perfectly. verify the timing and it's good, plug the timing wire back in and runs like crap again. so I think the ignition module might be bad and swap it out... nope, same problem.

Now i'm thinking it could be a ECM (PCM) problem or one of the inputs to it. As of now there are no CE lights and I have not checked it for any codes yet (just found out how last night).

So has anyone here run into this on a Chevy 350 before? year is 1991 1/2 ton truck, TBI motor

 

Well your problem is that its a chevy. You must have been on something when purchasing him a chevy, lol. But I dont have a clue on what the problem is. Have you checked the dilimabob thats connected to the whatchamacallit?

 

When I had an 86 Z-28 I ran into almost the same thing. It turned out to be the Mass Airflow unit. I have never really messed with a TBI motor, mine was a TPI. Could very well be that part though.

 

there is an ignition control module under the rotor in the distributor on those motors that has a propensity for intermittant failure. u should get that checked

 

Jakebrake should be able to help with this one now that i think about it he had that old chevy!

 

Very true but dont those usually just die? I have never seen one show signs of failing.. just dead and thats it. Not saying that isnt happening, just curious if anyone has seen one slowly die.

 

Ok so no Mass air flow for TBI, sorry I never owned one, all my chevys were either TPI or carb's. Anyways the MAF was replaced with a MAP sensor.
My guess would be the MAP sensoror the Ignition Control Module like Tommygunz stated.

 

forgot to mention.. .swapped it already.

 

I'd think a map sensor would toss a code & lite up the CE light... there is no CE light at this time. the CE light is functional however as it does lite up when we yank the timing wire.

Squirt... I tried to tell him [sm=chairshot.gif] during our debug sessions I mentioned that if it were a dodge, we'd had it fixed by now...

 

ran in to simulor prob on a 94 blazer it happend to be the distributor.
it had some play in it making amissfire & running poorly.