Over the past week or so my car has developed a "buck" in it. Every once in a while it just jerks for no reason. I noticed that whenever it does it my tach jumps up a few hundred RPM. So last night I took a long drive with Craig's software and found out that the RPM signal is jumping all over the place. The whole drive was below 2500 RPM - yet a good portion of the tach signal was over 4000 RPM, even over 6000 RPM a few times.

Does anyone have any idea what could be causing this? I don't really think it's PROM related - but I've been messing with it so much lately maybe I screwed something up by accident.

TIA,

Scott

Sounds like RFI from a bad plug wire, or something of that nature.
Bruce

Thanks Bruce, I think you hit the nail on the head. I measured the resistance of the #1 and #3 wires tonight, which have the most clearance around my headers, and they were both over 12k ohms.

Now where's my Summit catalog.....

I'm really happy with some Magnecors I've been running (10mm).
Crane, and MSD iin that order as alternatives in my book.