Intermittant dying

[formercruiserhead]

1989 k5 blazer stock tbi 350. Had several issues last summer with it dying sitting in the driveway idling and also on the road. Did several tests but was so intermittant that there was no certain problem found. Anyway long story short ended up replacing entire distributor and ecm using my prom chips. No issues for the rest of the summer. Them driving home one day starts running bad, check engine light and dies in the driveway and wont start. Tried it the next day still wont start drive it into the garage on the starter and it fires up. Left it all winter start it up yesterday idles fine then after about 5 mins stumbles almost dies and keeps idling with intermittant rough idle. No codes, wasnt up to operating temp yet.

 

[Wes Harden]

Sound suspiciously like a fuel delivery issue.

 

[formercruiserhead]

Sound suspiciously like a fuel delivery issue.

Like a faulty fuel relay?

 

[Wes Harden]

Could be 1 of a few issues. I find that if a relay has burned out normally the load it controls is drawing many amp. ie fuel pump.
But my jump to fuel delivery might be premature.
As far a codes go the ecm can only see electrical problems. Sensors and actuators.
With a tbi if runs watch the injector spray should be a nice even come, no gaps in the pattern.
Need to check for vacuum leaks.
Hoses, base gaskets intake gasket.
Iac may be lazy, or dirty.

 

[bradshawtech]

Check the wiring harness that passes over the top of the transmission right behind the distributor, I had a 89 K5 that had a shorted wire from a sharp casting ridge of the transmission, same intermittent description as yours.

i finally figured mine out as the only thing consistent in getting it running again was when I messed with the main wiring harness, moving it around cleared up the short for a time until the harness moved back to the shorted location from vibration and operation of the truck.
I’m betting you moved the harness just enough when you changed the distributor.

 

[formercruiserhead]

Could be 1 of a few issues. I find that if a relay has burned out normally the load it controls is drawing many amp. ie fuel pump.
But my jump to fuel delivery might be premature.
As far a codes go the ecm can only see electrical problems. Sensors and actuators.
With a tbi if runs watch the injector spray should be a nice even come, no gaps in the pattern.
Need to check for vacuum leaks.
Hoses, base gaskets intake gasket.
Iac may be lazy, or

Check the wiring harness that passes over the top of the transmission right behind the distributor, I had a 89 K5 that had a shorted wire from a sharp casting ridge of the transmission, same intermittent description as yours.

i finally figured mine out as the only thing consistent in getting it running again was when I messed with the main wiring harness, moving it around cleared up the short for a time until the harness moved back to the shorted location from vibration and operation of the truck.
I’m betting you moved the harness just enough when you changed the distributor.

Thanks I think it is a wiring issue as well. It is very random. Were you able to see damage? I replaced my tub and removed the harness and reinstalled into the new tub and have always thought it probably wasnt good for the harness.

 

[bradshawtech]

Thanks I think it is a wiring issue as well. It is very random. Were you able to see damage? I replaced my tub and removed the harness and reinstalled into the new tub and have always thought it probably wasnt good for the harness.

I couldn’t see the damage clearly, many 22 gauge wires in there. I made the repair by feel but it was clear that the problem was because of the sharp cast ridge it was laying on.

I’ve made this suggestion to others before when they described their intermittent problems and no one ever has said that theirs was the same source of trouble, one day it will help another, I hope.

 

[formercruiserhead]

Ok looked all over the wiring nothing looked bad or rubbing against anything. Pulled the IAC connector off and nothing changed. No check engine light no change in RPM nothing. Replaced the IAC valve and did the set up. Old one was worn. Set the idle and drove it around. Seems to be fixed, didnt stumble or act like it was going to die. However toward the end of my test drive the idle seemed high again. Will have to double check throttle cable and pedal to make sure it isnt catching. Throttle cable is new. The only other thing I can think of is, is that this was originally an automatic trans and I swapped in a manual trans without changing anything computer wise. Would the idle be high because of a set rpm for the auto vs manual trans? So it thinks its in park all the time? Is there something like jumpering the trans connector somehow to make the computer think it still has the auto trans? I dont think these computers are that smart.

 

[dyeager535]

Been so long since I had to think about this...

Yes, the programming is different in the ECM's (PROM actually) but as I recall the thing that was done was to fool the ECM through the park/neutral switch. The setup/idea would be the same on any of the TBI car stuff, and likely TPI as well, so google will probably net you some answers.

I just can't remember if you want to fool the ECM into thinking it was in gear all the time, or in park all the time. Neither is technically "optimal" since things such as timing were different between the two trans, but I can't recall anyone saying they absolutely could tell the difference when driven.

 

[formercruiserhead]

Ok so here was the fix. I kept getting random issues. Short cutouts and check engine light on very dim. After driving would come on fully and throw a knock sensor code (42?) I think. Anyway replaced the ecm with a new one. And replaced the IAC to get rid of the knock sensor code. Been driving for a couple weeks with zero issues zero check engine lights.