1989 K2500 Running Rough

[Kylow11]

Hi everyone, I’m new here but I’ve been reading these forums for working on my ‘89 K2500. The issue I most predominantly have is that it will randomly idle very rough until it dies. Give it a little gas and it’ll run, but still not great. It eventually levels back out (sometimes). The other issues are new, which leads me to believe that this whole thing is an electrical problem. The parking brake light randomly came on and won’t go off, and my blinker will periodically act like the bulb is out (it’s not). I recently hit a speed bump (slowly) and it started running rough and the blinker went out at the same time. Then a few seconds later, magically started being right again. I have started trying to find the ground straps and wires to check those out but I’m scratching my head here. I have already changed the ICM, distributor, wires, PCV valve, IAC valve, rebuilt the throttle body, changed the fuel pump, filter, and relay, changed the coolant temp sensor, and checked all my fuses. Any guesses on what to do now? And if anyone has pictures of where all the ground straps/wires are located that could be affecting this, that would be great. Thanks in advance!

 

[Schurkey]

it will randomly idle very rough until it dies. Give it a little gas and it’ll run, but still not great.

Connect a scan tool, look for codes, but especially look at the data stream. See what the sensors and outputs are doing when the truck runs poorly.

Verify fuel pressure under load.

The parking brake light randomly came on and won’t go off,

Verify that the park brake pedal is fully retracted. Any stiffness in the cables, and the pedal doesn't return all the way. It can bounce against the switch as the truck goes over bumps. Alternatively, you may have a problem with the wiring, or the safety switch on the brake combination valve assembly. The park brake pedal and the safety switch turn on the same light on the dash.

and my blinker will periodically act like the bulb is out (it’s not). I recently hit a speed bump (slowly) and it started running rough and the blinker went out at the same time.

Define "blinker".

Do you mean one or both turn signal indicators on the dash? Or do you mean one or more of the actual turn signals at the front and rear of the vehicle?

Have you inspected the wire harnesses on the steering column? Perhaps a loose or corroded wire on or near the ignition switch (not the lock cylinder.)

I have already changed the ICM, distributor, wires, PCV valve, IAC valve, rebuilt the throttle body, changed the fuel pump, filter, and relay, changed the coolant temp sensor, and checked all my fuses.

Stop replacing parts, start doing real diagnosis.

And if anyone has pictures of where all the ground straps/wires are located that could be affecting this,

That's in the Genuine GM service manual set. Select service manuals can be downloaded from this site.

 

[df2x4]

Here's the link to the service manual downloads.

https://www.gmt400.com/threads/88-95-service-manuals.43575/

 

[454cid]

Define "blinker".

Do you mean one or both turn signal indicators on the dash? Or do you mean one or more of the actual turn signals at the front and rear of the vehicle?

I would assume it's at the tail lights... it's super common for the boards to go bad, doesn't matter what year. They never really will look bad either, but for awhile "fixing" them involved taking them apart looking at them and putting them right back together. Sometimes it would last a week, or sometimes a month. I tried several sets of boards, used 2nd design GM, used 1st design GM, New US made Globe Specialty boards...all junk. The ones that lasted were made in Taiwan and sold by Orielly Auto.... Dorman possibly. I eventually had to replace those too, but they lasted for years. Now, I've simply purchased a set of complete new boards/housings made by TYC and they seem to work fine.

On my truck it was always the left side causing problems.

Our tail lights are just designed stupid.