VR crank sensor issue

[Martin Wagner]

I have been running a microsquirt on a Mazda Miata race car since last fall. I am using a 36-1 Ford crank wheel with an Escort VR cam sensor. I am running the version 2.883j code. This has been working fine until this summer. Now the car will start and run fine when it is cool but after a track session if you shut the car off and try to restart it in 5 to 20 minutes, it will crank fine but the engine will not start and the tach doesn't move. Let the car sit for an hour or 2 and it will start again.

I think this must be in the VR sensor input circuit since both tach and coil outputs fail and return at the same time. Anyone have another idea?

I plan to replace the VR sensor and recheck the wiring but I have never seen a VR sensor that is temp sensitive. Could this problem be related to the VR overdriving problem that some people have reported? If so, have I fried the microsquirt? If it is the overdriving problem and the microsquirt is OK, would the series resistors fix the problem?

Marty

[SQLGUY]

VR pickups ARE temp sensitive. They lose amplitude at higher temperatures as well as lower RPMS. So a hot VR pickup trying to pick up a cranking signal is going to be the most likely failure scenario if the amplitude is a bit low. This would therefore be underdriving the input, not overdriving it.

If you have a resistor in series with your VR input, you might want to reduce that resistance a bit. If you don't have a resistor there, you may want to try adjusting the clearance between sensor and wheel a bit to see if that helps.

[Martin Wagner]

Didn't know VR was temp sensitive! The sensor is right next to the lower radiator hose so that might compound the problem. I don't have a resistor in the VR line but it is a fair distance from the wheel (> .060"). I'll move the sensor closer to the wheel and see if that helps.

Thanks,
Marty