Nevermind. You did it correctly.

 

Interesting. The only thing wrong with it is there is an extra crank pulse. No idea why, but I'm guessing that it caused the megasquirt to lose sync and basically **** the bed until you restarted.

 

I installed a new crank position sensor and no change. It's an Intermotor unit from CARQUEST. I have a new Mazda unit on hand I could try. What say ye?

 

I had a feeling that had something to do with it.

Based on the pic of the composite log, go space your crank sensor further away from the wheel. I bet that solves your problem.

 

But how? I'm not saying you're wrong, I'm just having trouble getting my noggin' around it.

Sooooooooooo, everything is going fine and I have a crank angle sensor fail. **** happens. It's like a bad ballast on a fluorescent light. It's not completely dead, but not functioning 100%. I install a new replacement, but it behaves exactly the same way. How can the system that's my engine and electronics suddenly need an adjustment?

I've already made the adjustment, but I haven't taken her out yet.

Thanks much,

 

The crank sensor on a 99+ miata ouputs a square wave digital signal. But internally, the actual element that senses the changing magnetic field (caused by the teeth on your crank wheel) is a VR sensor. The signal from the VR sensor is a sinewave that varies in amplitude depending on RPM. The sensor itself has the circuitry inside it to take a sine wave of varying amplitude, and convert it to a constant amplitude square wave signal. Great design, it minimizes noise by putting the signal conversion hardware right next to the sensing element.

Ideally the sensor is spaced at such a distance that the sensor can pickup an actual pulse at say, 100 RPMs on the starter with a dead battery, and at redline, without the internal circuitry failing to count a real tooth, or, picking up a noise pulse and thinking that is a pulse.

It is possible that your sensor is so close to the crank wheel that a noise pulse (caused by who knows what- crank vibration for example) is enough to trigger the sensor. Moving the sensor further from the wheel will reduce this amplitude, potentially reducing the noise pulse's amplitude enough that it no longer triggers the sensor's circuitry inside to cause it to count that as a tooth.

If moving the sensor further from the wheel solves your problem (if), then you reduced the amplitude of the signal and noise, and the noise reduction stopped the false trigger and hopefully it can still see the actual tooth at low RPMs.

 

Sir,

Fantastic explanation. I appreciate you taking the time. But you miss my confusification. How could it happen with two different sensors? In other words, what would cause my car to suddenly need a larger crank position sensor gap (if that actually works) than it did before?

 

I don't have every answer, sorry. If moving the sensor fixes it, then I'd say maybe the old sensor vibrated and got closer, or the crank is now vibrating in a way that caused it to pickup a false tooth, or who knows what? From memory I thought .040" was the proper gap, and you said you used less than that.

 

I'm having the same issue here. Right at redline WOT pull. Stock ECU was behaving the same way before I installed my MS3. Pulled a code for cam position sensor over retard. Did a new cam position sensor along with a crank position sensor from o'reilys. Might try to go with an OEM crank position sensor and double check the gap. Shouldn't it be fine as long as it's within the FSM specified range for the air gap? I attached a log you will see how RPM drops right at about 6600. Engine doesn't respond to any throttle input until you switch gears and it syncs back up.

 

Which MS3 ECU?

built it yourself?
MSPNP-PRO?
MS Labs's MS3-Basic?
Mine?


I see I was totally off base with the boost cut once I actually looked at the logs.

 

Rev built MS3 basic but like I said this issue was there when I had the stock ecu in the car.

 

well on yours youre losing the cam sync.

 

What else could it be besides a faulty cam position sensor? I've already replaced the crank position with an aftermarket one and the cam position sensor with a new OEM one. I can try another new one? I hear that crank position sensor is a culprit since they are on the same circuit or whatever.

 

Alrighty then. Since the car was cold this morning, I swapped in the Mazda-provided, Japanese-built crank position sensor. All is well. No dropoff or CEL. She's a beast since the retune.

I hope CARQUEST will take the new defective CPS back. I had to wait for the Mazda part to arrive. The CARQUEST part was in stock. Seemed like the right thing to do to try the box store part. Lesson learned.

Sooooooooooooo, I have Noise Filtering OFF. Should I turn it back on?

Thanks for everyone's time and advice.

poormxdad

 

Turn noise filtering back on.

Did you try the carquest sensor with more spacing by chance? What is the new mazda sensor spaced at?

Glad you got it fixed.

 

Pat,

I did not. Swapping that part out is an asspain, so I wanted to do it when it was cold.

I shot for 0.045" and got 0.043" when it was all done and tightened up. I'm thinking it won't matter. The CARQUEST part was defective. Interesting how it had exactly the same faulty behavior as the part that was in there before.

If CARQUEST gives me my money back, I may purchase another Mazda part for the spares box.

Thanks again,

 

I'm a fan of mazda sensors, I don't blame you there. Still, if the carquest was at .031" as you said, and new is at .043", that could have been the problem with the carquest part, it was too close and that sensor's internal circuitry could not deal with the signal at high RPMs. Goes along with your "interesting" part too. I would guess mazda's can work with the sensor close to the wheel, it would make sense for there sensor to have a "correct" setting, but also be able to work with human and wear induced tolerances.

 

I'm not taking it out again, dammit.

 

Gents,

Just had my first chance to drive her with the new sensor after turning Noise Filtering back on. The drop off and CEL is back, but this time at about 6400 rpm.

Are there any negatives to turning Noise Filtering off and keeping it off? I'll probably try a larger gap first, but this really has me shaking my head.

poormxdad

 

This worries me. I just put a new OEM sensor in and it fixed the issue I had like you are. Really hoping I don't have to be carrying spares around. Fingers crossed.