T.B.I. Stumble/hesitation on accel.
 

Alright folks, I am starting this one up to pick the brains of the masters here at 67-72. I wanted to start one of these that actually ends with the solution. There are a million of these threads out there that never get to what the eventual fix was.

This is on an 89 S10 Blazer with a 4.3. I know a lot of it will be relevant for TBI period, as my 5.7 TBI in my 87 r10 shares a lot of the same components.

My little brother picked up the Blazer for something he could dd. Scored it cheap, and it idled like a dream. Guy told him that it had a hesitation under load and he couldn't figure it out. test drive once it was towed home confirmed a pretty bad stumble.

Here are the few steps I have taken so far

1) Checked fuel pressure - Good 11-12PSI at tb (15 at filter)
2) inspected injector spray pattern. One of them was just spitting out fuel. Replaced filter & both injectors with new units. Rebuilt throttle body. improved overall driving but still stumbles on acceleration
3) tried to unhook EGR to test, no improvement.
4) Unhooked IAC, ran better with only minor hesitation
5) Installed new IAC, hesitates on initial throttle but otherwise accelerates fine (although maybe a bit sluggishly still)

I will be replacing the Coolant temp Sensor, TPS and MAP sensor when they come in tonight.(I already have them from a 4.3 swap I was going to do that never came to be) And will update with results.

Any suggestions/guidance/experiences welcome. Regardless I will keep posting results for reference, since this seems to be a common issue.

Re: T.B.I. Stumble/hesitation on accel.
 

Just posting an update here. I had it running pretty well after changing the IAC. I also changed the pcv valve and that seemed to take away the slight hesitation. Now it ran normal, just a little bit sluggish. I changed the coolant temp sensor thinking maybe it was out and running rich. After that the alternator went out. I changed it, and its running funky now. I will be resetting the idle and doing a reset for the IAC, I think things got a little out of sorts from the low voltage and then being disconnected to replace the alt.

Re: T.B.I. Stumble/hesitation on accel.
 

update*

After doing a reset of the IAC and Adjusting the idle on the TB, it seems as though I have it running pretty well now. going to try and smog it this week when I get some free time.

Re: T.B.I. Stumble/hesitation on accel.
 

Change the fuel filter. You should not see a drop like that through the filter. Also check TPS and make sure it is adjusted properly.