Miata K24 swap Trigger 1 error at high RPM

[Rodan]

Miata racecar with Honda K24A2 swap.

I'm having an issue on-track where the car is cutting out at high RPM at full throttle.  The problem did not occur on the dyno, only on-track, and almost entirely at RPMs over 5000.  Obviously, this makes it difficult to replicate/diagnose.

Logs show Trigger 1 (crank position sensor) error when the problem is occurring.  I'm working on uploading a log, but the file is a little too large for the native upload, and I'm at the track so resources are limited at the moment.

I have checked continuity of signal, ground from ECU to sensor, and it appears good, even with some vigorous wire wiggling.  Power circuit supplies several other functions and those have not been affected.

I replaced the crank position sensor with a brand new Honda OEM unit and it made no difference.

Looking for any ideas that I can try here at the track to get through this....

[Adamw]

Use google drive or similar to share the log.  Also a copy of the tune and a trigger scope captured at 5000RPM would be useful. 

[Rodan]

Sorry for the delayed response.  We were on the road, and I'm finally home and managed to capture a log and trigger scope.

The car has degraded to the point where it's nearly undriveable, and the cutout is happening while revving in neutral.  I've attached a log, and a cranking trigger scope.  I have been unable to capture a trigger scope at higher rpms because of the cutting out.

Since my previous post, the CPS wiring has been pulled out of the harness and run directly to the ECU, with physical separation from the rest of the harness.  It's still the shielded wiring, and continuity has been rechecked (good for both signal and ground) to ECU.  The CPS connector has been disassembled to check the crimps on the wires and those are good as well.

ECU Log 2024-06-22 3;45;55 pm.llgx Trigger Scope - 2024-06-22 3;48;17 pm.llgx UMS Tune 5-2024 mod1.pclx

[Adamw]

Your scope has mostly only captured the engine sitting still before you started to crank.  Can you do another, this time click capture when the engine is running.  Preferably around 5000RPM where the error occurs.

[Rodan]

Unable to get the engine to rev past ~4600rpm at this point.  Here are scopes at (approx) 2k, 3k, 4k and 4.6k where it's cutting out badly.

Trigger Scope - 2000rpm.llgx Trigger Scope - 3000rpm.llgx Trigger Scope - 4000rpm.llgx Trigger Scope - 5000rpm breaking up.llgx

[Vaughan]

There is a big spike in your trigger 1 signal that shouldn't be there and it is causing a trigger error which will be the source of your misfire, I usually assume that noise from the ignition coils causes this kind of thing but @Adamw will probably be able to provide more in depth insight.

[Adamw]

As Vaughan says, there is a large voltage spike coming into your trigger 1 signal which is big enough to be counted as an extra tooth.  I also initially assumed it would most likely be related to the ignition system, but when I started testing your map on the bench I found the spike doesnt really occur in a position that lines up with where I expect a spark to occur.  The spike appears twice in your 5000RPM log, both times it occurs at about 225°ATDC#1.  The closest spark events under those conditions would be #3 at about 145ATDC and Ign 4 at 325ATDC, so quite a way off.  You do have a lot of ign trims in your map and knock control, limiters and trigger errors could potentially cause more range than expected but my feeling at this stage is it is unlikely ignition related, although there are still possibilities like ground offsets causing a random spark etc cant be ruled out.  

So it is a bit of a puzzle, I dont think it is a bad connection in the trigger wiring as one of the spikes goes to a voltage higher than the pull-up.  A failing sensor could cause it since they are powered by 12V, but if you have already replaced that I think we can rule that out for now. 

The only thought I have come up with so far is possibly the VTEC solenoid could generate a spike like this - I dont know for sure if the mechanical action of the pin that locks the rockers together could cause the spike to occur at the same crank angle both times but that may be a possibility.  That seems a bit far-fetched to me but I dont have any other bright ideas right now and it is an easy one to rule out.  Try running it with the VTEC solenoid unplugged will be a quick way to confirm if this is related to VTEC.

FYI, in the scope below, the teeth I have marked in green rectangles is the normal expected "extra tooth" on the crank wheel, TDC is 2 teeth to the left of this.   The "tooth" in the red rectangle is the spike that shouldn't be there.  

[Rodan]

Thanks... I will try unplugging VTEC tomorrow to see if anything changes.

[Rodan]

Scopes with vtec disconnected and vtec and vtc disconnected.  No difference in the car... still cutting out badly above 4600rpm.

Trigger Scope - 4k no vtec no vtc.llgx Trigger Scope - 4k no vtec.llgx

[FWombat]

@Rodan Did you have any luck resolving this problem?  I'm currently chasing a very similar issue on a K24 swap, though mine is more intermittent than yours.

[Rodan]

I believe I have.

When I had the car tuned on the dyno, the idle air control valve melted down, literally.  I had used an aftermarket part, not knowing any better, and it was clearly defective.  We unplugged it, and the tuner tuned around it, car runs fine.  I never plugged it back in, so the connector was just tied back against the harness.  I completely forgot about it until after we returned from our two track weekends.  I eventually went back and looked at the connector...

I could not reproduce any conductivity across the connector pins, no mater what I did.  I did, however, cut the connector off the harness and isolated the wires and my problem disappeared.  The working theory is the carbon from the melted plastic was creating a short across the contacts while the engine was running and under load.  This connector shared the 12V+ supply with the crank position sensor so I believe that short was causing the voltage irregularities that led to the crank signal error.

I have run the car at two autoX events since, without any issues.  I'm back on a road race track next weekend, and that should settle the question.

[FWombat]

Interesting, that's a great tidbit!  I'm running an e-throttle, and so the IAC connector on my engine harness is dangling unconnected.  

I hadn't even thought about unplugged harnesses that share the same voltage supply as the crank position sensor.  I'll clean those up and see if it helps.

[Rodan]

I don't think that connector would have been a problem if it had not melted.

[FWombat]

For the sake of posterity, this connector was not my problem.  My trigger error issue ended up being a wiring problem.

On my engine harness, the injectors share a 12V wire with the crank and cam position sensors.  Then there's a separate 12V wire for the ignition coils.  I had both of these 12V wires connected to a single source wire from my Razor PDM.  Once I separated them, my trigger errors went away.  I guess the load of the ignition coils was enough to sometimes cause a voltage drop that made the crank sensor not function properly.