OK, the knock sensor on my 85 IROC was not hooked up when I got it. The end of it appeared to be damaged and the wire was up by the right strut mount. I drove it like this for about a month while I worked on other things, rarely it would ping, never had a check engine light. I did a full tune up over the weekend. Accel cap, rotor, Accel coil, plugs, Summit wires, air foil, Fram Air hog filters, oil change, and I installed a new knock sensor and plugged it in.

I noticed that the check engine light was blinking while I was at a stop. The engin was running fine. It went away as soon as I accelerated, came back on at the next stop, but was very dim, and still flashing. Now its gone all together. I bridged A and B on the ALDL, the fan came on but its not flashing codes.

I have done a few searches and some posts say this means there is a PROM problem, I had thought that maybe it was misfiring at idle and thats why the light was flashing.

Just looking for same advise. I have a spare ECM, but not sure where its located in the car. Any help appreciated, the car is running great otherwise!

 

Is it storing any codes? It might be time to try your spare. It's where the glove box should be.

 

Well, drove it again today, no light this time. It does seem to misfire a bit above 50MPH in 4th, had a little bucking going on nothing to get worried about and after a few miles it was fine. I will recheck everything this weekend and fix a couple of vacuum lines that I know are spongy, maybe I have a small vacuum leak causing the misfires. I didn't think about it yesterday, but I did fill the car up on Sunday and it was pretty low, maybe the Shell station didn't get the best gas. I usually get it at QT.
I'll throw the other ECM in if I get the light again.