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-   -   Help with crank pos sensor (http://www.jeepforum.com/forum/f12/help-crank-pos-sensor-1524862/)

epettit 05-17-2013 10:07 PM

Help with crank pos sensor
 
I need a little advise .... I recently put the 4.0 head and fuel injection system (ODB1)on my 4.2 and it has run great. Recently after I have turned it off and let it sit a while it would crank but not start. I would shoot a little freeze it on the Cps and it would fire right up.

I have heard not to run a Cps other then jeep so I purchased a factory CPS from jeep and low and behold it would not start after I went to leave after driving out for lunch.

I was curious why heat causes these to fail and can they be insulated?? Is there another brand to try?

Any help would be appreciated

epettit 05-18-2013 01:12 PM

Any help out there?

laybackman 05-20-2013 08:45 PM

Quote:

Originally Posted by epettit (Post 15447844)
I need a little advise .... I recently put the 4.0 head and fuel injection system (ODB1)on my 4.2 and it has run great. Recently after I have turned it off and let it sit a while it would crank but not start. I would shoot a little freeze it on the Cps and it would fire right up.

I have heard not to run a Cps other then jeep so I purchased a factory CPS from jeep and low and behold it would not start after I went to leave after driving out for lunch.

I was curious why heat causes these to fail and can they be insulated?? Is there another brand to try?

Any help would be appreciated

Are you running a header? They generate more heat. Wrap the CKP wiring in several layers of aluminum tin foil and see if that helps.

epettit 05-20-2013 09:15 PM

I am running the factory 4.0 header... But will give it a go. If that does not work I might get an old one from pull apart

idaholtby 05-20-2013 09:25 PM

Quote:

Originally Posted by epettit (Post 15447844)
I need a little advise .... I recently put the 4.0 head and fuel injection system (ODB1)on my 4.2 and it has run great. Recently after I have turned it off and let it sit a while it would crank but not start. I would shoot a little freeze it on the Cps and it would fire right up.

I have heard not to run a Cps other then jeep so I purchased a factory CPS from jeep and low and behold it would not start after I went to leave after driving out for lunch.

I was curious why heat causes these to fail and can they be insulated?? Is there another brand to try?

Any help would be appreciated

How long has this rig ran with the new set up? Has it ran fine and now this is a new issue? What model year 4.0L ECM are you using for the MPFI? Sorry for all the questions, just need more info before formulating a possible answer. Oh and for clarity, when you say CPS, you are referring to the crank position sensor and not the camshaft position sensor in the distributer?

epettit 05-20-2013 09:44 PM

Yes it is the crank pos sensor.... The whole setup is out of a 91 Cherokee . It ran for a couple of weeks with no issues but the weather is warming up.

It seams to fail when it's sits for a while and heat soaks the sensor. If you let it cool or hit it with a little freeze it and it fires right up


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