Can't figure this out...TBI and hesitating on acceleration

[wczimmerman]

Replaced parts:
1. TPS
2. EGR valve
3. ICM (Echlin brand)
4. Entire engine (all new motor from GM)
5. Injectors
6. Distributor cap/rotor (10K miles on it)
7. New coil (10k miles)
8. New spark plugs and wires (10k miles)
9. Battery

Fuel filter has 30K on it. ICM was replaced just 2 weeks ago. I noticed right away that the motor seemed to pull stronger afterwards. The alternator is suspect right now: with all electrical accessories on and giving it some RPM's it is only providing 12.9V at best.

The issue is a hesitation from a stop and today I noticed it when I was climbing a small hill...it will normally do it only for a second but up the hill it did it several times in a row (I wasn't giving it a lot of gas). The truck is running great otherwise...very smooth. When the ICM went it left us sitting on the side of the road. Could the alternator voltage cause this issue? I'm running out of parts to replace.

Thanks for your help!

 

[Georgeb]

30,000 on the fuel filter??? If thats not a typo change the filter. Otherwise whats your timing at? Mine hesitated off the line quite a bit. I havend gotten rid if it completly but bumping the timing to 10 deg advaced made it almost unnoticable. Just thoughts off the top of my head right now.

 

[wczimmerman]

30,000 on the fuel filter??? If thats not a typo change the filter. Otherwise whats your timing at? Mine hesitated off the line quite a bit. I havend gotten rid if it completly but bumping the timing to 10 deg advaced made it almost unnoticable. Just thoughts off the top of my head right now.

Nope...you read it right: 30K. How often is it supposed to be changed?

The timing was checked within the last month and a half or so. The truck was doing something similar when the ICM died. I suppose the ICM could be bad again after a couple of weeks...

I'm going to replace the fuel filter and alternator tomorrow and start with that.

 

[CSFJ]

I seem to recall the recommended service life of the early fuel injection filters being fairly short. I almost want to say it was around 5000 miles. I may be mis-remembering, but I know I was surprised by it.

 

[wczimmerman]

So, I spent all day Saturday working on this. I replaced the fuel filter, air filter, and PCV valve as maintenance items while I was there. The fuel filter wasn't the issue. I also replaced the coil (new with the new motor mentioned in the OP) with a new Accel coil-still no solution. I finally took the ICM out and replaced it with another one from NAPA which did the trick. Why the first died after 2 weeks is unknown to me.

Fast forward to today (Tuesday) and the truck is at it again: same symptoms. My wife was driving it and was getting the "hesitation/shudder" then it died twice on her and wouldn't start until she took the key out and let it sit for a while. So, I now have an ACDelco ICM in my hands and I will swap it out tonight.

Anything else I'm missing here? Could it be that the aftermarket ICM's just aren't reliable or rugged enough? This is a brand new distributor and I've applied the grease that comes with it each time.

 

[CSFJ]

Aftermarket electrical stuff gets a little more hit and miss with each passing year. When I was chasing an issue on my '88, I swapped most of the sensors. None were the problem, and I did eventually find the culprit. Been lucky so far, but I kept all the original sensors just in case.