MegaSquirt losing crank signal

[Digitalwave]

Air gap should be 1.0mm +/- 0.2mm. You can use a feeler gauge on it easily. Clean it up, gap it, and if it still occurs, buy a new OEM (and only OEM) CPS and I bet it solves the issue.

[reelizmpro]

Glad this was bumped. I've been trying to figure out the cause of my drop out a while now. My CPS resistance and gap is spot on but has a dent on the side and the wiring is stiff and old. I installed a plastic one which gave me problems almost immediately. Looks like I'll be ordering a new OE BMW one soon.

I read about an O ring that's supposed to go on the sensor but don't recall ever seeing one.

[Digitalwave]

Barry, the one I had problems with tested fine but also had a dent on the side. A new metal OEM CPS fixed it immediately.

[nando]

I don't think there's any o-ring - there's nothing to seal, the sensor is on the outside of the engine. probably, sensors that come with an o-ring are generic, meant for use in multiple cars where the sensor could be installed in the block.

I've been fortunate to never have this issue, except early on in my ownership of the car when the clips for the wire were missing and it rubbed through the sheathing, shorting out on the water pump pulley. That is probably worth checking, as every E30 has had many water pump/belt changes over the years, and often that clip gets broken or thrown away, people not realizing how important it is.

That also means I bought a new OE sensor when they were "cheap", lol. Going on 10 years with my Megasquirt-3 and it's never given me a single problem!

[reelizmpro]

Strange both of ours had dents in the side. New BMW sensor is on the way from ECS. Yeah there's no O ring. That must have been a reference to another engine.

[Yuri]

Just went to the dyno and unfortunately had the same issue at 4,500 rpm. Glad I found this thread! Sent from my iPhone using Tapatalk

[Kershaw]

Still chasing this problem. I can go past 4k. If I am not at full throttle, like 70% throttle, then it'll cut out at 5k. In neutral the rpms will go up to 7k full throttle which is scary because the redline is set at 6300rpm. So I don't know what that's about but I'm guessing it's a separate issue. I bridged VR- in J5 and VR+ in J6 with a 10k resistor as well as gave R9 2 turns counter clockwise. I'm assuming that R9 is the crank sensor potentiometer, even though it is not labeled as such. See attached picture before the shunt was added.



I'm assuming since I get throttle up to 7k in neutral, it is not a timing issue? The AFRs seem very stable at 12.9/13 AFR @ 8 PSI at full load when it cuts so I am assuming it is not fuel related even though I am only running 19lb injectors at this time. Since I am assuming it's not timing, not fuel, I am looking at spark. I changed the dwell setting from 3.7 to 3.2 and instead of a hard cut at 4k it was a short cut and then it kept climbing and cut at 4.5k again before I could back off. So I bought NGK 5122s/BR7Es spark plugs and will install those and see if that changes anything. I will gap them to .23. Of course, with CX Racings beautiful but large turbo manifold, I am assuming I will end up having to remove the manifold to replace the spark plugs. Joy.

Any further suggestions are appreciated.

[Kershaw]

I changed the spark plugs to NGK 5122 gapped to .23 and added 42lb injectors. No change to the issue. A new CPS is arriving tomorrow.

[varg]

Did you run a tooth log while revving out and look for lost sync/pulse pattern? Just odd that it doesn't miss in neutral but will under load. I don't know if you have a single coil or not, but at 4,500rpm you only have 3.4ms of available dwell with a single coil. From a spreadsheet I made many years ago:

[Kershaw]

I'll check my dwell settings. I've looked at the tooth logs but I either miss the drop or it's not there. I'll post one.