castock

Hello. My all stock original equipment (all smog equipment in place and connected) 81 is doing the following:
Runs great, for 10 or 20 miles, then check engine comes on and it loses power; no missing, just flat and slow. If I disconnect the battery, check engine goes away and it runs great again until this issue recurs. I checked the timing when the symptoms are present and it is not advancing. I also bridged the first two (without a divider) terminals on the ODB1 port and it did not tell me anything, just stayed steady on. One last item, with the key in the run position, but engine not running, a relay mounted on the fire wall above/behind the brake booster is clickety clacking to beat the band. Thank you in advance for any wisdom.

terry82

Motor runs good till it warms up?then I would check the coolant sensor in the front of the motor.that one talks to the computer.could be computer, but I would start with sensor.

Antz81

If you are not getting any codes at all when checking, then a sensor is not likely to be the problem. As you know you should see code 12 when checking for codes. Since you get nothing i would start by checking the continuity of the wires from the test port to the computer. If that all checkes out then you may need a new computer.

64roadster

Make sure you're grounding the correct two terminals. Since you did not get any response I bet you're on the wrong end of the OBD connector.

RC81

How did you check the timing? Harness to the dist. disconnected?

ramair_bryan

After replacing a couple computers in my time, I've found it's not the computer at all.
It's the $180. chip inside that pops..........

The computer it seems is well fortified. But the chip calls all the shots.
I agree, no ''12'', no link to diagnostics.

Use a flat screw driver to bridge the 2 plug in ports at the connector. Can't go wrong that way...........

Tim81

One more thing, I don't know if it matters but you need to short the diagnostics terminals before you turn the key on. Good Luck

7T1vette

I would offer one other suggestion before you throw money at the problem: disconnect battery, remove all connectors to the computer and clean contacts on mating connectors with alcohol and Q-tips, then remove/clean/replace all GROUND connections to the computer.

Connect battery, fire it up again, see how it runs, and again try to get any trouble codes. If you do not get a response of "12" [and any trouble codes that were thrown], you can either buy a new chip or a new computer...your guess is as good as ours as to which is the problem source.

Antz81

As long as the engine isn't started then it doesn't matter. I have always turned the key on first and then shorted the terminals