Miata with PNP RPM fall 0 intermitanly
 

Hi All,

Have a 94 NA Miata with a new PNP MS installed. During a wide open run, RPM will fall to 0 and come right back intermittently. Tried a different CAS with just about the same results. Hooked a scope up and the signal is pretty dirty, but the odd thing is that the crank signal goes from 0 to 13v and the cam signal goes from 0 to 5v. Anyone ever see this before? When I check voltages at ECU with CAS disconnected I get 4.8v on 2G(Y/L) and and 10.8v on 2E(W). 10.8v is what battery voltage was at the time. https://cimg6.ibsrv.net/gimg/www.mia...8cc04c482f.jpg

Those are the expected voltages. Can you post up a composite log of the loss of RPM? This will give everyone more to go on.

Sure thing Matt, here it is. This is just a free rev without the motor under load. Let me know if I can provide anything else that will help.

Can you direct me to where you are finding the spec that shows one channel over 5v? Everything I find says both should be square wave 0-5 volts.

Thanks!!

PNP Megasquirts based on the microsquirt module have 12V on the crank, 5V on the cam.

You're getting noise on the CMP signal on frame 3.

Thanks!!!

In your opinion is this a bad CAS or a CMP signal that needs some shielding?