350 TPI Fiero

Don Burns donburns at macconnect.com
Wed Sep 27 02:35:23 GMT 2000


>Most of the PCMs/ECMs I've seen have been mounted on a plastic bracket.
>Absolutely no electrical ground through that! If the ground wires are
>grounded properly there should be no need to ground the case.

Hmmm... I was really surprised to hear all the responses about no need to
establish a local ground for the ECM case. Even Howell mentions the
importance of HEI shielding in their TPI Service Manual for Vette, Camaro
and Firebird. Admittedly Howell did not mention local grounding but
multiple grounding especially at the case certainly will not hurt. And in
fact it provides redundancy should another ground wire open up. What
stimulated doing this was I stuck a probe connected to a low frequency
spectrum analyzer inside the ECM box. What I found was a pattern of noise
(engine running) about 6db above the noise floor with the engine off. With
the case locally grounded the noise level dropped 5db, a significant
reduction. But alas, the root problem is still there. Anyway, I now have a
noise free ECM.

Wish I had more time to work on this bloody thing but its gonna be another
week before I get the time... Next tests will be done with the scan tool
and somebody else driving as well as checking performance with O2 sensor
mentioned by Shannen

Don


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