I've noticed lately that on a wot run, my rpm will read say 3075rpm, then 3025 then 4000. It happens several times during a test run at wot at different rpms. I realize that the ecm sees the rpm from the ignition module on the GM hei.
So I've changed the module, checked the wires (msd's) and still note it.
I'm running an msd 6a ignition-this is on an 86 vette.
It doesn't seem to effect anything, but I would think it would have to?
Has anyone noticed this with any other scan software?
I guess next I'll try it without the msd 6a, and I'm also going to change the plugs just to try and rule out those as a source of the problem.
I'd think it's a diacom quirk, but a few other cars I've scanned don't read this way, and I don't remember mine doing it in the past.
Oh yea-with my wide band rpm pu-it shows a smooth rpm increase without those "down and ups". Could it be the ecm?
Ideas???? Thanks!