87FCTurboII

iTrader: (2)

Info up front: 87 Turbo II, MS3X (using stock CAS, wired with shielded wire per Aaron Cake's writeup), VR pots all the way out (also per Aaron Cake).

I've been having a couple issues since installing my MS3X a couple weeks ago. The first is my idle: it seems to be hit or miss. Sometimes it will idle perfectly smoothly, other times it oscillates from ~600-1200 rpm. At first i chalked this up to my BAC valve, but the idle pwm % isn't changing enough to cause that large of an oscillation. The second issue is what I 'think' is detonation at 6000 rpm, full throttle. Again this is hit or miss, it happens half of the time, and it's just one quick detonation event (like one popcorn kernel popping). I've pulled timing, added fuel, and spent hours looking through data; all without getting rid of the knock or finding its root cause. This led me to look at the crank signal.

Attached is a screenshot from my composite logger while the car was at idle. The lines on top show triggers from the 2 tooth wheel, bottom lines from the 24 tooth wheel. The first 3 triggers up top are equally spaced, and span 12 triggers from the bottom line. After that, additional (erroneous?) triggers are being picked up occasionally on the top line. The rpm signal remains correct throughout.

Before I break out my tiny screwdriver and start spinning some pots, does anybody have ideas as to what could be fundamentally wrong here? I kept the "unshielded" parts of the cam wire as short as possible when adding shielded wire to the MS3X. My shields are grounded to the ecu grounds also. Is it normal to have to adjust the pots on our cars?

And FYI, the car runs nearly perfect aside from the 2 issues I mentioned.

Thanks!

Aaron Cake

iTrader: (1)

The idle variation simply sounds like a lean section in the VE table around idle. Probably a dip to the left of where it idles, as well as one above.

Are your shielded cables grounded only at the Megasquirt end? CAS connector in good shape?