MSD & Megasquirt RPM variance

[Porsche_911s]

2.7 - MSD 6200AL - Tbiz EFI Megasquirt

I have a question for all those running MSD and Megasquirt.

Is your RPM readout in the Megasquirt software steady? Mine seems to jump 200 to 300 RPMs in the upper RPM range even when I know I have the car running at a steady pace. At idle it does not seem to jump and I can achieve a steady idle. I would not worry about it but since Megaquirt needs this RPM for obvious reasons, this problem seems to be contributing to slight surging in all gears when the RPM variance causes MS to jump in-between VE settings.

I am getting my MS RPM signal from the MSD unit's aux port. My tach signal is coming from my 2.7 dizzy. No adapter is required.

Ground was the first thing that came to my mind. The engine, body, and MS unit are all properly grounded. The MSD unit is mounted on the hardware provided which are rubber mounts. Should I ground the MSD chassis?

Any suggestions or comments would be greatly appreciated,

Stephen

[Porsche_911s]

Bump

[Scott R]

I had a variance and it was noise in the 12V signal from the fuse we tap into in the engine compartment. Seemed like it was supplying a dirty tach signal to the MSII.

[Porsche_911s]

Oh... So the power for the MSD unit may have issues. Where did you end up getting power from?

The main power wire for the MSD unit is coming off the starter lug. But I only used automotive grade wire. Not sure if it is shielded.

[Scott R]

Originally posted by Porsche_911s
Oh... So the power for the MSD unit may have issues. Where did you end up getting power from?

The main power wire for the MSD unit is coming off the starter lug. But I only used automotive grade wire. Not sure if it is shielded.

In my case I was using the original braided plug wires and the 12V back to the MSII brain was resting close enough to the wires that it was picking up coil noise.