Not a question, but an observation about how old electronics can drive you nuts and the importance of checking EVERYTHING......

My brother's 87 GTA had a Minirammed 409ci monster dropped under the hood August a year ago with custom TPIS chip to run it thru the stock ECM. We got it running and drove it 250 miles to his house in 90* heat 2 days after firing it for the first time. It ran OK, got decent mileage, but had a nasty idle miss and off-idle stumble.

Over the next few months my bother tracked down some vacuum leaks, played with the fuel pressure, dialed in the timing, etc. Ran better but the idle was still bad. He drove it back up and we went over the motor with a fine tooth comb- all the mechanical stuff. Like I told him from the beginning: "I built you a good motor- look elswewhere for your problem."

And he did. The number of bad electronic parts he replaced to fix it was astounding, however.....

First off, the alternator was found to be bad- the diodes were leaking AC into the car's DC power system. Replaced with new and there was a small improvement in idle quality. He tested the distributor module and it tested bad. Replaed. Car ran great for a day then regresses into bad idle behavior. Replaed entire distributor (original was physically worn out). Ran great for a day then idled bad again. The F-word was used liberally. Retested the module. Tested bad again. What the F??? Decided something was killing the module. Tested the ECM- after HOURS of probing, testing and running down shop-manual diagnostic trees it was found the ECM had a bad ground (several actually). Replaced with a junkyard ECM and suddenly the thing ran GREAT. Better than it ever had.

One day later it developed a high-RPM lay-down. A "wall" almost. Hair was ripped from scalps Three Stooges-style. Fortunately it was quickly traced to a fuel pump relay that chose that exact time to go flaky. What are the chances?

NOW it runs perfect. Not just close, but perfect. Only took 9 months to trace everything down! Old electronics should ALWAYS be considered suspect. Check them before you decide you need to throw parts at the car. It doesn't take much for 20 year old electronics to turn a good engine combo into a miserable daily driver.

A side note- Under no circumstances could we have paid anybody to do this work for us. They would have charged thousands if you could even find anyone who really knows how to diagnose this stuff properly. This kind of diagnosis must be considered DIY work. A factory shop manual and lots of patience are the critical ingedients.

 

How much $ was your junkyard ECM?

 

$25. Third gen ECMs are cheap and interchange with a bezillion other GM cars. This one was out of a Buick Skyhawk 4 cylinder! All you have to do is swap your chip into the junkyard ECM (of course) and reinstall the whole mess under the dash.

The junkyard guy will have a Hollander Interchange Manual that tells him which ECMs out of which cars will work in your particular year/model car. Then just head out to the yard and yank it out of the "donor" car.