I've posted this message before to the forum, and all responses seem to point at the opti-spark, which now has about 57k on it. I haven't gone to pull it yet since its so damn cold here in Michigan, and my son has taken over the garage with his cars in various states of distress.

Anyway I've still been driving it about 100 miles per day to work and back. When it warms up it goes into its misfire, backfire & stumble routine above 2000 rpm. If I'm cruzing or rev it up a few times, it will set the SES lite and run fine till I stop it. Some times, the SES lite will go out by itself, and then the problem comes back.

Well I wanted to confirm the opti-spark, and see what code it sets, so I got a cheapee OBD1 code reader, its a Actron 9001..... makes the SES lite flash the code. When I follow the directions and plug it in, turn on the key...it does not turn on the SES lite, or flash it even. When I set it for the ABS codes (No ABS Brakes for awhile, just the inop lite) its the same thing, with no flashes for the codes.

So this evening (it got up to 30 deg. during the day) I did the simple diagnostic from the Helms manual for checking the "serial data line". This involves connecting an Ohm meter to the A and M ports of the data link connector. I disconnected the 3 modules connected to the serial data line, the PCM, Diagnostic Energy Reserve Module, and the Electronic Brake Control Module. This then showed an infinite ohm reading, or open circuit.

Next step is to reconnect each module, turn on key, and check for any voltage. I connected each module individually and got a 4.5 vdc reading for each, including the "black" connector on the PCM.

The way I read the manual says that if I get a voltage reading, then that module needs to be replaced.

Are there any other tests that should be done to confirm these modules are bad?
Can all three modules really be bad at the same time?
Should I even be trying to read the codes with this cheapee code reader?
Could the PCM be warming up, and messing up the opti-spark?

I hate to buy all three modules (probably $100 each), and find out that they are not it.

As usual any help is greatly appreciated!

'94 z-28, m-6, and now 217k

 

Hey, neighbor! I know what you mean about the cold. I'm over in the Creek and it's too dang cold to spend the few minutes to pull my MAF to port it indoors!

Anyway, I got a cheapy code reader from AutoZone and even though it says not to start the car, its the only way it would flash the codes. It didn't fry anything but that's no guarantee your code reader won't smoke so try at your own risk.

Anyone else have any experience with this?