MS3X with random hiccups, RPM dip, runs great otherwise

[thebigjrs]

Hello Everybody,
I just recently got and installed a MS3X 3.57 in my 300ZX TT. I got it tuned to the point where I can drive it around for longer trips and I've been noticing some random "hiccups" on my drives. This doesn't result in sync loss, and I'm sure the RPMs aren't dropping that much as the car is maintaining speed, is manual and I'm in gear. I'm very confused how this would happen without sync being lost. I've attached a log of the run. It happens at at 333 and 360 seconds on log 46, 360 and 560 on log 47. The RPMs do seem wavy, which I don't know if it is normal or not. Any help would be great, can't wait to get tuning some more!

[thebigjrs]

I took a composite log today. Looks like there is a problem between 539706 and 539892. Looks as if it's losing signal than catching up? It's also strange that it's losing the primary and secondary triggers at the same time, which is why I'm guessing it's not seeing a sync loss?

[Matt Cramer]

If both signals go away, but there is no lost sync indicated, you're usually looking at some dropped serial data rather than a loss of signal. However, Optispark mode can do some rather distributor-like things including losing the signal without losing sync. And that seems to happen a few times in the log you posted. Try adjusting the VR trim pots.

[thebigjrs]

I will try turning both pots counterclockwise all the way. Right now they are r52 all counterclockwise and r56 2 turns clockwise. Would a misfire cause a RPM drop and composite log like this? I'm wondering if my PTU is on its way out.

[thebigjrs]

I tested the ECU with the POTs turned all counterclockwise with no change. I also put the old ECU back in to verify that it doesn't do it when it's installed, to verify proper CAS and PTU operation and it ran smooth. Would onboard SD Card logging cause this sort of dropped serial data. I do have it logging as many variables as I can all the time.

[thebigjrs]

I think I may have got it after playing around with the VR pots. I ended up around 3.5 turns clockwise on r56. I disable all card logging prior to doing this with no change. Thanks for the suggestion Matt

[thebigjrs]

Still no dice, I think it's better, but still skips a beat once in awhile. I was looking though the source code and I found something saying that the low res signal is only used for initial sync and re-sync. Does this mean the low res signal, that I change with the VR pots is only used on startup? I will continue to play with the pots, but if anybody could enlighten me on this that would be awesome. Thanks

[Matt Cramer]

Sounds like the documentation may have a mental typo - it's the high resolution signal that is only used at startup and low RPM.

[thebigjrs]

I'm at 7 turns clockwise on r56 and 4 on r52. I've tried everything in between. The only possible things that would create this rpm dip could be software or the CAS right? Any other suggestions would be awesome. My next logical step would be a new CAS.