TBI Issues

[ShortBus]

Take any of my suggestions with a grain of salt as I'm new to TBI myself. I've got mine running pretty well now after a new tbi unit. Have you checked voltage at the blue wire on your TPS?

 

[RoryH19]

Right, it's going to take some time to track down.
I've thought about a new TBI.

 

[1987 GMC Jimmy]

Here are some tests for the EST Circuit that can help isolate a faulty ECM, ICM, or wiring. I think this is Camaro literature. The test procedure in the truck manual sucks IMO.

I’m having a similar issue to yours that I have still not been able to completely iron out, but I’m closing in fast. I’ve been having a cold stumble, lurch, whatever you want to call it, that’ll stabilize after a moment, and then it’ll pop and cut out more and more the closer you get to WOT. I’ve noticed it has to get to closed loop operation to really give you the middle finger. Mine was intermittent, but it’s grown less so. It finally tripped a Code 42, which the computer defers to the ignition module’s default timing curve when that happens, and then it runs perfect.

My ICM tested bad recently, which I replaced that, the wiring looks good around the distributor, but I still have to test a good spare ECM I have on the road or run this diagnostic procedure step by step. Since the ECM has to come out either way I figure I’ll just swap in my Jimmy’s PROM and CALPAK, plug the other computer in, and take her for a spin.

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[RoryH19]

Here are some tests for the EST Circuit that can help isolate a faulty ECM, ICM, or wiring. I think this is Camaro literature. The test procedure in the truck manual sucks IMO.

I’m having a similar issue to yours that I have still not been able to completely iron out, but I’m closing in fast. I’ve been having a cold stumble, lurch, whatever you want to call it, that’ll stabilize after a moment, and then it’ll pop and cut out more and more the closer you get to WOT. I’ve noticed it has to get to closed loop operation to really give you the middle finger. Mine was intermittent, but it’s grown less so. It finally tripped a Code 42, which the computer defers to the ignition module’s default timing curve when that happens, and then it runs perfect.

My ICM tested bad recently, which I replaced that, the wiring looks good around the distributor, but I still have to test a good spare ECM I have on the road or run this diagnostic procedure step by step. Since the ECM has to come out either way I figure I’ll just swap in my Jimmy’s PROM and CALPAK, plug the other computer in, and take her for a spin.

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Thanks for the info. I'll need to spend some time over the weekend to hopefully find the issue. My k5 build is burning all of my spare time.
Sometimes it will run "normally". No surging, no back fire, consistent power no matter if mild acceleration or pedal to the floor. Then it will surge or backfire at times. It did this yesterday. I was accelerating, mildly, and then gave it a little more pedal. As soon as I did backfire. Let off, accelerated again, no problem. I came to a stop and when I accelerated I put it to the floor, no problem.

Still no SES light or codes.