89 1500 Acceleration problems after warm-up

[jcormic]

Please Help if you can because I am pulling my hair out and I am BALD!

Ok here goes: I have an 89 1500 with 350 TBI, 700R tranny, 68,000 miles (Yes only 68,000 miles). It has been running great and then one day I was pulling a ski boat and at about 60 mph I felt a really slight Miss but it did not occur any more for about a month then it became more frequent until one day out of the blue it became so bad I could not accelerate hard or it would almost stall out and then backfire. When the rpms would rise it would all of a sudden take off with some missing. So naturally I thought my dist. was bad.

When this started I checked the Codes and throughout the whole problem from the start til now not ONE code other than the imfamous 12 blinks at me.

Never one to do things half way... I replace the Dist., Dist Cap, Rotor, Plugs, Wires, Air Filter and PCV. Set the timing to 0 deg. with the timing advance disconnected and when it was reconnected timing went to the advance mode and idled fine. It would run fine with only an occational miss until it was warm and it would start the hard studdering again.

Talked to a GM service manager friend of mine and he told me to change the TCC on the Tranny. So I changed it and the fluid and added some Lucas Tranny treatment. Same thing only a little better no hard stalls on acceleration just studdering like the timming was messed up so I checked it again and it was right!

When the rpms climb to a point on a hard acceleration it will all of a sudden take off almost like normal then when I let off and the rpms drop and I accelerate again at a slower rate it studders but will eventually even out. This happens in with the tranny in OD, D, and some in 2.

We talked again and he convinced me to change the EGR and the ECM temperature sensor. (I replace the O Sensor about 18 months ago) Well it was a little better but once warm it would act up again. It just took a little longer for the problems to start. Again not as extreme like I just mentioned!

Next I thought Fuel system. So I changed the filter and the Pump and in tank filter. No improvement.

A guy at work thinks it is the crank shaft position sensor or the Throttle position sensor. I don't mind changing either and am to the point of just changing every stinking sensor... yes event the O Sensor again.

I am also ready to replace the Cat. and even ECM...Nothing would be left except for the Radio ;-)!

I don't mind the outlay of money I just want my truck running again, RIGHT, and would appreciate hering if anyone has a solution so I don't have to spend every non-working hour on this problem....My wife and kids would like to have a Dad again instead of a Full-Time Mech.

Thanks in advance for any help!!!!!

[Fireplug]

dont blow your money on a cat just yet. Take a vacuum reading at idle and at 2,000 rpm while in park . post the readings.
Check the wiring on the crankshaft sensor and see if its wet with oil or anything else. I have seen a lot that where covered with oil and eat the wires and connector. There is also a egr vacuum sol. that controls the egr make sure its working . what type of plugs you using ? AC/Delco I hope. did you replace the entire dist or just the cap and rotor??
Please tell me again what its doing and what are you doing at that time.

[broughy84]

also make sure the knock sensor on the passenger side of the block is hooked up and working....these will make your truck run like shit.

[jcormic]

Thanks for the replies and help and my truck is back to it's old self.

So here is what I did...I went home and replaced the EGR Sel., the Coil (Went from an Accel HP to a stock coil) and replaced the O sensor. One of the three fixed it. My guess is the O sensor was bad but the coil winding box had become unglued and was wobbling in the frame/outer winding. There was no metal to metal contact but the wobbling could have caused enough variance in voltage to throw the computer out of whack. The Sel. was for good measure and preventative sense I replaced the EGR valve... I should have thought of that ...Thanks for the suggestion.

For info purposes the the vaccum pressure was 20 at idle on excelleration it droped down to 5 and then at between 2000 and 2500 rpm would recover to 20 again just like it should. This was the same before and after the EGR sel. swap.

The craziest thing is that the ECM NEVER complained and NEVER set an error code despite the fact that the truck was running and backfiring soooooo badly.

Do you guys think I should swap computers because of the lack of error detectioh and code sets?

Thanks Again!

[KRSEB5]

i am haveing the same trouble ive replaced the fuel filter o2 map plugs wires cap roter drained the fuel tank was new when i bought the truck cut the cat. converter offand put new injecters on the TBI
engine idles perfect but when i put it in gear and step on the gas it studderrs unless i floor it then it goes fine but speed is limited should i do the distributer and coil? i'm lost help

[jcormic]

I learned my lesson..... Try the $19 Oxygen Sensor...... It's the cheapest thing and I found out from an GM Shop Manager that the Bosch are only good for about 10 - 16,000 miles.