Hey everyone,

My 1989 Fullsize 5.7L V8 Jimmy is having some issues. It has a little over 200k on it, so just about anything could be failing at this point. Still has the original engine and tranny.

I bought the truck about 6 months ago. Since I've owned it I've felt like it needs to fight a bit too hard to start (needs to crank too long). Soon after getting it, code 42 - EST Circuit Failure. I replaced the Ignition control module and it went away. Then a few days ago I started the engine, and the rpms went very high. I turned it off and on a few times with the same result. I did not drive it, then later that day I tried again and everything was fine when I started it, however obd code 42 was set again. The next day I could not start it at all. Just keeps cranking, but won't turn over.

Not sure what to think about this. I originally thought maybe a temperature sensor was broken so the engine was running fast to warm up, but now I can't even start it at all, and code 42 is set. Anyone have any insight? Pickup coil maybe? Or ECM, since maybe that was why the RPMs were going crazy?

Thanks a lot for any input. It is much appreciated. By the way, does anyone have a wiring diagram for a 89 Jimmy or K5?

 

Did you ever get anywhere with this? I have been chasing a pretty large draw in my 89 blazer and today I managed to narrow it down by pulling the ECM B fuse. I don't have a reader, but it's throwing a code as well and I have no idea where to go from here to fix this. Just thought maybe you're troubles might shed some light on mine.

 

You actually shouldn't need a reader to find out what code is set. Just stick a paperclip in the top right two ports of the diagnostics port. Here's a description - GM Check Engine light Codes without a Scan Tool

My symptoms of not starting and high rpms went away, but I still get sporadic check engine light warnings. Along with the 42, 22 started showing up, so I ordered a new throttle position sensor, which should be here in a few days. I also just put a bottle of the injector cleaner in my gas tank to see if that would help.

 

Although I have traced my problem to something else, thanks for that link. I knew about the paperclip business, but didn't have any idea what meant what. I'm new to this vintage ECM system and early OBD. I pretty much have only had pre-1980 trucks or post 2000.

 

Just out of curiosity, what did your trouble code end up being, and what was the fix?

 

Actually I haven't gotten as far as codes. Turns out my most immediate problem is a short in the ECM "B" circuit somewhere, diagnosed with good old fashioned fuse yanking and a multimeter. I just changed a cylinder head and with all that entailed I have no doubt I'll have a couple of codes to sort through once the short is repaired.