92 B2600i ecu won't output codes

I have a 92 B2600 that was running perfectly then one day it began idling rough but after driving it a while it went away. The check engine lite never came on while driving but now it won't start w/o using starting fluid. When it does start it has no power A/C won't come on and the check engine lite stays on all the time. The computer won't flash the codes by grounding the green single wire diagnostic connector and the check engine lite just stays on. There is voltage to the diagnostic connector but grounding it makes no difference, I have used this connector sucessfully before to set the timing but not to read the codes. I suspect the ecu is at fault, does anyone have any other ideas?

Hey, I got a 93 2600i. It runs good, once in a while it might stall as I am approaching a light, probably the i.a.c. valve. My check engine light came on recently and I had a friend pull the code with his snap-on scanner..........no codes present!!! He even "made" a code by disconnecting the O2 sensor at the front of my intake manifold, the code popped up, that meant the computer is working properly (communicating). I sent an email to someone at Mazmax here in Houston describing my problem, they told me that the check engine light automatically comes on for maintenance, and that the only way to reset it is to disconnect a harness behind the instrument cluster and re-connect it in the plug next to it. I am fixin' to do it this coming weekend. L8Rs