Misfire only on track

[curly]

I've been having a reoccurring intermittent misfire with a customer's car. It's a '96 Miata with a G4Xpnp, with the stock CAS wired to a '01-05 cam/crank trigger wheel to have functioning VVT. On the street and dyno, I can never get it to misfire.

Here in the pacific northwest, the first few sessions are cold and wet, therefore slow, and the misfire never happened. It finally did misfire 19 minutes into the 3rd session, I swapped crank sensors with a .045" gap, it misfired again, and on the 5th session I set it to .020" (just trying things). It still misfired, but once it stopped misfiring, I could keep going for a couple laps. I parked it for maybe 2 minutes while it continued to idle (perfectly), and then did another 20 minute session with no misfires. Owner then took it out for another 20 minutes, again without misfires. 

I see the RPM go to 0, and trigger errors increase to an eventual 22 on the "session 5" log, 255 in the "session 4" log. 

After it happened the first time, i did de-loom the engine harness, and tug on all connections, with zero issues. 

Does anyone see anything obvious I'm missing? Is there anything I should log that would help pinpoint the issue? Only thing I'm realizing now is I'd love to have VVT data, but unfortunately I didn't have logging set up for that. Besides that, the trigger error counter is only on trigger 1.

Tune attached, and here's the logs:

https://drive.google.com/file/d/1IVJiVTaIHipNfGhkXTlJLPt2UKxMxv9V/view?usp=sharing

https://drive.google.com/file/d/1U2a-S8odX5EsvqzyXzMGE6832MH-B5gc/view?usp=sharing

PIR HOD tune.pclx

[curly]

Here's a picture of the trouble area on the log, but perhaps the lack of reply's indicates it's probably a physical problem with the car? 

[aerace_fab]

trigger 1 goes crazy, step's I would take is to physically examine the wiring from the ecu to the crank trigger connector, then the terminals. Are you located in washington?

[essb00]

Those that you call 'misfires' were actually trigger errors. The ECU is cutting both fuel & ignition when it 'lost' the crank position.
Check the wirings of your crank trigger. Also, attach trigger scope captures at different RPMs (where you mostly get the trigger errors) and attach here so the experts can check.

[curly]

6 hours ago, essb00 said:

Those that you call 'misfires' were actually trigger errors. The ECU is cutting both fuel & ignition when it 'lost' the crank position.
Check the wirings of your crank trigger. Also, attach trigger scope captures at different RPMs (where you mostly get the trigger errors) and attach here so the experts can check.

That's my bad, I just figured "trigger errors as a result of loss of trigger 1 signal" was too much of a mouthful vs. "misfire". I was referring to the loss of RPM. If you look at ignition and fuel cut during that time, it isn't cutting anything, however at zero RPM it's also not injecting any fuel, so my theory was the AFR spikes were a result of that. The first thing I looked at was fuel/ign cut, to see if any of my protections were kicking in.

On NAs with a single CAS on the back of the engine, you need to extend the wiring to the front of an NB motor to run the crank trigger sensor. I cut the CAS pigtail off, spliced in a length of 22 gauge tefzel wire twisted together. Doesn't need to be twisted, but it makes it easier to loom. I did peel back the loom and tugged on all the connections. 12v and GND are spliced to the cam sensor as well, which never has sync issues, so at least that half of the splice hasn't shown issue. Obviously it's a 30 year old car this year, so it could be any of the factory wiring as well, I'll take a closer look at the ECU.

I checked the trigger scope at various RPMs, looked ok to me, but I'll capture and post at different RPMs tomorrow. 

11 hours ago, aerace_fab said:

trigger 1 goes crazy, step's I would take is to physically examine the wiring from the ecu to the crank trigger connector, then the terminals. Are you located in washington?

I'm in Oregon, this was at Portland International Raceway. I should also note, this happened every time while exiting turn 7, leading on to the back straight. Normally I would attribute this to the particular amount of G forces in this corner, however, being a clockwise circuit, I find it interesting that it didn't happen on any of the other right handers, only this one. And again, after the a couple dozen "trigger 1 sync losses", I could continue driving 20-40 minutes without any issue. I also considered the battery sliding around in the trunk like they do sometimes in NAs, but no other voltage issues are reported, and the battery was checked and is secure. 

[essb00]

Loss of trigger sync = Loss of RPM. It wouldn't show as %Fuel Cut or %Ign Cut, but it should be understood that the ECU will not make both fuel injection and igntion events when it does not know the crank position, thus you see AFR spikes.

[curly]

Here's the trigger logs at idle, 2500, 4500, and 6500. I don't see anything wrong with them, but maybe someone else does. This was warmed up, but obviously different from 20 minutes of track time. I've read about the stock 4 toothed wheel having trigger issues on other aftermarket ECU triggers, so I may try changing it to a 36-2 wheel and see if it makes a difference. But this is the 3rd NA I've wired with NB sensors on a Link, and I've tuned 2 other NBs, this is the only one I've had issues with. 

Trigger Scope 2500 - 2024-05-6 7;31;09 am.llgx Trigger Scope 4500 - 2024-05-6 7;31;30 am.llgx Trigger Scope 6500- 2024-05-6 7;31;46 am.llgx Trigger Scope idle - 2024-05-6 7;30;36 am.llgx

[Vaughan]

No obvious issues shown in those scopes, I have however seen non genuine NB crank sensors missing teeth completely despite being being spaced properly, this presented as a misfire at idle.

Does your crank sensor have the pictured bit of sheathing on it? The non genuine sensor I had didn't and the genuine one did.

[curly]

Yes, all three of the sensors we've tried has that. I swapped crank sensors with another NB at the track, and he never had issues the rest of the day, my issues came back immediately.

I'm glad the trigger scopes look good, I'll inspect the trigger wheel closer for damage, but otherwise I may try a 36-2, and look deeper into the wiring. 

[Vaughan]

with the trigger scopes you really need to get a scope exactly when the issue occurs, you need to see that trig 1 state reset to idle and you need to see where it failed in regards to the teeth and what state it was in prior to failing

 

[curly]

I can't even return to idle with the trigger loss, much less return to the pits where my laptop is, but I hear you. 

Is there a trigger state I should be logging? Or is that only with the trigger scope? Also, how do you open a saved trigger scope? I can't open it unless I'm connected to the ECU, am I missing something?

[koracing]

I would try running 3 wire tefzel from the sensor all the way back to the ecu.  Also try swapping ecus with another to see if it's the same and definiltey harness or sensor related.

The only issue I recall having with heat on a miata was coils getting too hot over time and starting to misfire.  I reduced dwell in that particular case and that resolved it (that car was on a HydraEMS at the time, and very hot days in the summer).  Perhaps if it's related to that the misfires are messing up the trigger signal causing the zero rpm reads?  Just a thought.

[Vaughan]

11 hours ago, curly said:

Is there a trigger state I should be logging? Or is that only with the trigger scope? Also, how do you open a saved trigger scope? I can't open it unless I'm connected to the ECU, am I missing something?

Maybe log these 3 and engine speed at 1kHz in the ECU logging, it might give enough info to see where it is falling over but it isn't as useful as an actual scope while it's failing which would show the actual signal.

I would also in general definitely recommend a 36-2 over the factory 4 tooth crank signal.

[Vaughan]

It appears I didn't attach the picture I meant to

[curly]

Ah ok, I was trying to figure that one out.

I do have those logged for the logs posted above, however only at 10hz IIRC. Trig 1 state flies between normal and "Blank time", "first tooth", "test gap", or "idle". When it's running correctly, it only goes between "count large", and "count small".

36-2 wheel is on the way, I'll have that installed, the above values set to 1khz, and I'm planning on disconnecting the VVT solenoid if it continues happening, swapping coils, and if all else fails, we have some shielded tefzel I may try to run from ECU to engine bay.