banditt1979

Well I was on here a few months ago about an 85 I was having problems with and several people helped me out. So I'm hoping the same help will come for the 1990 I picked up on the cheap. I noticed that the check engine light wasn't coming on, the aldl connector was missing, and the fan came on before I started it. As I found out today, someone literally broke out the check engine light. I also found the aldl and remounted it. So after I replaced the check engine light, turned the key to ON and it kept flashing code 12, like the connector was grounded. When started, it flashes constantly, again, its like the computer was grounded. I don't see where the A and B terminals are connected, and if I unplug the computer, the fan goes off (naturally). Does anybody know of a common problem that sounds like this with these cars? Or a procedure for isolating this problem? After I replaced the computer in my 85, all problems went away. Any advice is always appreciated!

Matt

don hall

Read through these links, and you will gain an understanding of the codes, especially code 12:

http://corvettephotographs.com/c4vettes/codes.htm

http://corvettephotographs.com/c4vettes/ecm.htm

banditt1979

Thank you seabright, I am already familiar with the codes themselves. Problem is I haven't grounded the aldl, its just acting like I did and won't stop.

Cliff Harris

The wire on pin B of the ALDL connector goes directly to the ECM. It sounds like that wire is pinched somewhere.

You should be able to measure about 5 volts on pin B (comes from the ECM), referenced to pin A (ground).

banditt1979

Thanks Cliff. It also occurred to me this morning that I could check for continuity between pin B and ground. I had a few to drink last night and my brain wasn't cooperating.

banditt1979

After some testing I determined that the wire on pin B was shorted to ground somewhere. After I disconnected it, the light went out. But it still runs with a stumble at part throttle. If you mash it, it takes off without any miss. Changed plugs and oil so far, the plugs didn't look too bad but what the heck. Its not setting any coded at this point, although it did when I set the timing so I know the computer is good.