very short sync loss troubleshooting

[9secz]

My MS3x installation has been working very well for more than 3 years. I've had minor tuning issues, but the car, which is my daily driver, has been a reliable.

Two weeks ago I took it to a drag strip so I could do multi-gear WOT tuning without being thrown in jail. Ever since that day, when I do my typical 3rd gear or 4th gear WOT blast, I get sync loss for 1 TS sample period. I'll attach a log later, but I think you'll find that the engine is working fine for many samples, then there is one sample of sync loss that nearly throws me through the windshield. then the engine wakes up and continues to pull. The sync loss occurs in the middle of the gear, not right after a shift, not right after boost reaches max, and not right before hitting redline.

Here's what I plan to do this weekend:
1) Pull cam and crank sensors for visual inspection. If they look fine, then
2) Put an oscilloscope on them and record traces with engine idling. If the signals look good, then
3) Inspect the cables and MS3 connectors for signs of wear or damage. If all that looks good, then,
4) Pull the MS3 and check the VR trim pots. If the pots are properly adjusted, then,
5) What?

BTW and FWIW, the AFR safety circuit prevented a full pass at the strip, but the car still recorded a 128 mph trap speed.

Jeff

[9secz]

Troubleshooting:
Step 1: cam and crank sensors and connectors look fine. I cleaned the contacts anyway.
Step 2: cam and crank signals are pretty clean with the engine idling:


Steps 3 and 4: I'll pull the MS out of the car next to check the trim pots.

Here is a screen shot showing the lost sync event. I'll extract a bit of log file centered on the event and upload it soon. Lost sync reason is the blue trace in the bottom graph. You can see the RPM divot in the white trace in the top graph.



Any other ideas on what might be causing this?

Edit: I've attached a piece of the log file that contains my sync loss event.

Jeff

[grom_e30]

have you got a msq to go with

[9secz]

Current msq attached.

Jeff

[Matt Cramer]

Try a 10K resistor inline with the VR sensor wire.

[9secz]

Try a 10K resistor inline with the VR sensor wire.

OK, I'll give that a try. Do you think the crank sensor output voltage may be getting too big at high revs?

Jeff

[Matt Cramer]

OK, I'll give that a try. Do you think the crank sensor output voltage may be getting too big at high revs?

Jeff

Precisely. VR sensors have a pretty wide voltage range from idle to redline.