Hey guys,
I'm helping a buddy of mine with his NA6 which is currently a crank no start. The car has a jackson racing blower on it running an MSPNP2. The car ran fine on this setup for awhile until I guess it died at the end of last year and thats when this crank no start issue began. He replaced the CAS (used) and the car ran for a day-ish but then died again. This spring I'm trying to help him get the car running again but I'm currently running out of ideas. While cranking, the MS loses sync which makes sense because the RPM signal drops out. It is a cyclic ~250rpm - 0rpm - 250rpm - 0rpm - etc while cranking. This seems like a CAS issue to me since thats the only source of RPM for an NA6. I checked the wiring/pins/connectors at the MS and at the CAS and found nothing wrong. He borrowed another (now 3rd) CAS from a buddy and the car is doing the exact same thing. I've ready the few other threads from years ago with similar-ish issues but none of them provided much useful advice for this issue. I didn't see anything wildly wrong with the tune and the car was running for most of last year on this tune so I don't think thats the issue. I flashed a base map onto the ecu just to be sure and got the exact same behavior of the RPM/Sync Loss.

Is there any way to "bench test" the CAS without an oscilloscope? Maybe (hopefully) I'm just missing something stupid, or he actually just happened to have 3 bad CAS. I will attach the tune file and a log of the crank no start. Any advice would be awesome...

 

Update,
I stopped over his place after work today to try some more stuff. White/Red wire at the CAS has battery voltage, Black/Green at the CAS has continuity to ground, and Yellow/Blue and White have continuity to 2G and 2E at the ECU connector.

I also got a composite log of the issue and I will link the log. As far as I understand, Blue is crank, Green is cam, and Red is sync loss? I don't totally understand how the CAS electronically works if it outputs both a cam and "crank" signal. The crank signal looks like a fine square wave but the cam signal looks strange. Hopefully someone that understands how the NA CAS works can enlighten me haha.



I also pulled the ECU and inspected the boards/components/etc and didn't see anything visually burned or broken but I'm not really an electronics guys. At this point I'm confident in the wiring and have doubts that 3 CAS would be "bad" in a row. I composite logged all 3 CAS and they all looked basically identical to the pic above. I also reflashed the current (3.4.4) firmware to the ecu and that made no difference.

 

Did you happen to take photos of the ECU board when it was out?

 

I did, here ya go:

 

I’d be reloading firmware and tune, maybe trying base map with only injector size changes too. Man it’s been a while since I’ve played with a CAS+MS, id love to compare to a working one. I almost always get rid of them. You’re a little SOL without a BP oil pump though.

id also be trying the ECU on another Miata, and checking basics on the car like grounds.

 

Yeah I wish I still had my NA6, would make trying parts a lot easier haha. I'm going to double check that the wiring is the same on the NA8 for the CAS and if it is I am going to try his CAS in my NA8. My car currently doesn't run still but I should be able to at least see if I get a clean RPM signal with his CAS on my car with my MS2 or not.

And on the firmware/tune side I've already reflashed the ECU with fresh, current firmware and tried a new base map and I got the same cyclic 250-0-250-0 rpm signal after both. I checked both of the engine grounds and they have good continuity and look intact. I did find this, but I've never personally heard of people doing this before: https://wiki.fome.tech/Vehicle-Speci...NA6-Grounding/

But I totally agree with your mentality. I want to confirm for sure with another car that at least the CAS or the ECU is definitely good or bad.

 

Yes that's a signal/ECU/sensor ground that's redundant. I see coolant and air temps rise during a dyno run that's reduced by cutting that, maybe some TPS noise goes away, but unrelated to your issue. You could try isolating the signals, I'd start by unplugging the cam angle sensor wire and see what just the crank reports. In the log at least, crank looks like a steady signal, cam does not. I think a CAS is supposed to be like an NB, 4 crank teeth and a 2-1 cam signal, although cam might just be long pulse short pulse. Some pics here, but you can't see cam in either of them: https://www.miataturbo.net/ecus-tuni...upgrade-57770/

 

Gotcha, I'll leave that ground wire alone then. Next time I get over there I will try isolating the signals and see what the data looks like. I appreciate the help so far Curly