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Unread 05-17-2013, 09:07 PM   #1
epettit
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2013 JK Wrangler 
 
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Location: San Antonio, Texas
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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

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Unread 05-18-2013, 12:12 PM   #2
epettit
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Any help out there?
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Unread 05-20-2013, 07:45 PM   #3
laybackman
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Quote:
Originally Posted by epettit View Post
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.
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Unread 05-20-2013, 08:15 PM   #4
epettit
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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
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Unread 05-20-2013, 08:25 PM   #5
idaholtby
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Quote:
Originally Posted by epettit View Post
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?
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Unread 05-20-2013, 08:44 PM   #6
epettit
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Location: San Antonio, Texas
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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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