Crank Position Sensor Why???

Why is it that unplugging a CPS will "magically" get my 88 4.0 XJ going? I've read the tech section in my Haynes manual, describes how it works. I need to unplug/plug mine every 3-4 weeks or so to get going.

Been thinking of installing a cut off switch. Or has any Jeeper figured out how to build a bypass circut?

Thanks,

Iceberg

I think its that it creates a better(new) connection by unplugging then plugging it back in. The pins are seating differantly or cleaner as they are pluged back in. Clean the connector real good befor you plug it back in next time and so if it will work longer. Not sure if this is the only reason but I'm sure its part of it. I'm sure otheres will chime in too.

Thanks, connectors are new, as is the sensor. I have also pulled my ECU connectors and cleaned them.

Where are you unplugging it, at the sensor itself on the bellhousing or at the connection in the engine bay? If unplugging it and plugging it back in enables it to start, it really has to be an issue with whatever connector you are futsing with. I can't think of what else it could be.

I would inspect all related electrical contacts very closely with a good light. BTW, the crankshaft position sensor provides a critical reference signal to the PCM (tells the computer the engine is cranking) so I don't think any kind of mods would be recommended.

Just get a can of connection cleander and some dielectric grease and clean the connections and put light grease on them. Thats what I do. The grease protects againts moisture. It really the same thing as putting dielectric grease on lightbulb sockets that might get some moisture.

Unplug the cps and measure the induced voltage with an ac volt meter while cranking the engine. I bet you're only getting about .25volts. You need about .4volts with .5volts being desireable. To get the voltage you need, take a long screw driver and rest the blade on top of the cps adjacent to the plastic encased part and tap with a hammer a couple of times to bend the cps mount closer to the tone ring, then check the voltage again. If you bend it too much, you'll have to replace the cps, so be carefull.