MegaSquirt losing crank signal

[Malcolm206]

Odd, perhaps the bracket is bent/damaged. Of all the m20's we have worked on the bracket adjustment is enough to make the CPS actually touch the relluctor wheel.

My mistake, when I was tightening the bolts on the bracket I wasn’t holding it firmly enough and it would rotate away from the wheel. I now have it set to 0.88 mm away from the wheel, which didn’t change the issue.


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[Digitalwave]

First try different resistors (you did already). Next replace the CPS with a new OEM metal CPS and set the air gap properly (1.0mm). MS is picky about how good the signal is, much more than Motronic. If those both fail to fix the issue, start tracing and testing your CPS wires in the engine harness.

[ForcedFirebird]

Odd, perhaps the bracket is bent/damaged. Of all the m20's we have worked on the bracket adjustment is enough to make the CPS actually touch the relluctor wheel.

[Malcolm206]

Try making the sensor air gap tighter, this happens to me a lot on installs. The stock ECU doesn't much care if the gap is too large, but the MS does. The two 13mm screws that hold the CPS bracket can be loosened a little and the bracket has wiggle room.

It seems to be as tight as it will go without modifying the bracket, but the CPS sensor still seems to have a decent air gap between it and the wheel.


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[ForcedFirebird]

Try making the sensor air gap tighter, this happens to me a lot on installs. The stock ECU doesn't much care if the gap is too large, but the MS does. The two 13mm screws that hold the CPS bracket can be loosened a little and the bracket has wiggle room.

[Malcolm206]

Does the Microsquirt have variable VR sensor inputs? On my MS3X 3.0 board I had to turn the VR trim pots all the way one direction (I think CCW, not completely sure) and then that same issue went away.

Microsquirt doesn’t have variable VR sensor inputs. I bridged the 25k resistor on the back of the board to try and fix this issue, but it had no effect.


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[citizen_insane]

Does the Microsquirt have variable VR sensor inputs? On my MS3X 3.0 board I had to turn the VR trim pots all the way one direction (I think CCW, not completely sure) and then that same issue went away.

[Malcolm206]

MS can be so frustrating sometimes! The CPS might be a symptom not the cause...

Stupid first question... how good are your grounds?


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They appear to be totally fine. All new wire with a solid ground at the original wiring point near the battery. There’s no distortion in the signal. I may try moving it to ground on the block just to confirm that’s not the issue.


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[justinpirie]

MS can be so frustrating sometimes! The CPS might be a symptom not the cause...

Stupid first question... how good are your grounds?


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[Malcolm206]

I recently installed a new 2.9L M20 with Microsquirt v3.0. I'm using the stock 60-2 toothed wheel and having an issue with the crank position sensor at higher RPMs. Once I hit around 3500 RPM, the engine acts like it's bouncing off a rev limiter/fuel cutoff. The tooth logger shows I'm completely losing the signal and counts as a loss of sink. I bridged the shunt resistor in the case, moved the CPS bracket closer to the wheel, and swapped out CPS sensors with another used one.

Any ideas what I should try to check next?

https://imgur.com/qkqnsvK

https://imgur.com/rBRMyhZ

https://imgur.com/NMVkGUo