TL;DR - Megasquirt PNP Pro is losing the 1 tooth side of the reluctor wheel on a NB2 Swapped 1990 Miata. Has anyone had this problem and fixed it?

​Car Specs:

• 1990 Mazda Miata Chassis
• 2004 Mazda Miata Motor (VVT Enabled, Sequential Fuel Injection, OEM Sensors)
• DIY Autotune MegaSquirt PNP Pro (Bought through 949Racing) for 90-93 Chassis
• ECU Mounted on rubber Isolators on dash
• All sensors are grounded to the same location.
• 2004 Engine Wire Harness with bare minimum wiring to run the motor
• Run log (Qualifying Session) and Composite log attached.

​Back Story:
During Qualifying at Barber Motorsports Park roughly 2 weeks ago the car was running great no issues. I posted my qualifying time and decided to come in. As I was entering pit road I bumper the car to neutral (like I always do) to coast down pit road and let the car cool down. as I was approaching the exit into the paddock I put the car in second gear and the car had 0 power and sounded/felt like it was running on only 2 cylinders and was struggling to run. Weird. So I shut the car off and we pushed it to our spot and started troubleshooting (and much more after we left). The Car has been running on the same configuration and setup for 10 months with 0 issues until the weekend at Barber.

Reviewing The Log:
The ECU is losing the 1 tooth side of the cam reluctor wheel. some times the motor will run great till 3k RPMs then sounds like its hitting a false rev limiter starts breaking up because it loses the 1 tooth side of the reluctor.

Troubleshooting:

• Replaced Coils with NEW OEM coils
• Replaced Spark plugs (with correct gaps)
• Recalibrated O2 sensor
• Replaced O2 sensor
• Replaced Cam sensor with new OEM sensor
  • Verified gap clearance from sensor to reluctor wheel
• Replace Crank Sensor with new OEM sensor
  • Verified gap clearance from sensor to trigger wheel
• Checked reluctor wheel for any imperfections
  • Check tightness on cam too
• Checked valve springs
• Checked voltage at the Cam sensor
  • 1 tooth voltage: 4.96 Volts @ signal wire
  • 2 tooth voltage: 496 Volts @ signal wire
  • Ground resistance .4 ohms
  • Power Voltage: 12.6 Volts
• Ran an isolated shielded signal jumper wire and received the same readings
• Checked voltage drop from the sensor to the computer and had 0 voltage drop in harness.
• Checked with an oscilloscope of PIN 3O. Saw both the 1 tooth and 2 tooth signals and the signal never dropped off. But watching on the computer the 1 tooth signal is dropping
  • When the signal drops off the RPM is also no longer in sync and the engine starts to break up.
• Checked the 4 LEDs on the side of the ECU:
  • 12 Volt is lit
  • 5 Volt is lit
  • RPM light is SOLID
  • the last one is lit

We reached out to DIY Autotune and they are just as dumbfounded about the problem as we are. We are leaning toward a bad ECU. Has anyone ever seen this issue or anything we may have missed when troubleshooting?

 

Did you replace the trigger wheel with another OEM one?

 

I did not replace the crank trigger wheel. We didn't see in either log that we were losing the crank signal. Did I miss something?

I was thinking to replace the reluctor wheel. but I would have to buy a cam because the reluctor is not serviceable.

 

I might have a cam. Let me check tomorrow night.

 

Day 16 - The engine is still acting the same. DIYAutotune has been great in helping us troubleshoot potential causes of the issue but those have all led to dead ends.

160+ views, is everyone else confused like we are?

 

Ask DIY to tell you where to probe in the ECU for the cam signal, after the MAX9926(?) to see if that's the possible cause of the issue.

 

Thanks for the suggestion Reverant, I reached out to DIY and they told me to I could I am going to give that a shot.

Since I don't have a oscilloscope I can connect to my computer, I took a video of the oscilloscope and sent this to them proving I was getting the correct signal to the ECU. You can hear the engine in the background not even being able to idle right. (Warning: crappy one man cell phone video):

 

That would still be BEFORE the MAX9926, not after. You need to check AFTER the MAX9926.

 

Day 25 - Finally fixed the issue. Since DIY Had no clue what was going on we decided to rethink what happened coming over track. VVT kicks in at 3000 RPMs and while on track I was never below 4500 RPMs so VVT was always engaged until I bumped it to neutral and the motor dropped to idle.

Long story short we ordered a brand new VVT actuator from Mazda Motorsports (talk about not cheap) in a last ditch effort. This of course was the issue. The actuator is stuck full advance throwing the timing way out of band for the ECU to read losing the single tooth on the Cam trigger. So now we are going to see what broke in the actuator (hopefully serviceable) and add an actuator to the parts bin to take with us.

We do see VVT err in TunerStudio though and I am not sure what could be triggering it. Does anyone have any ideas on where to start diagnosing the VVT Error? Should I start a new thread?