4.0 ZJ turns over but won't start - Page 5 - JeepForum.com

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post #61 of 81 Old 09-01-2013, 07:46 PM
Oldfrog
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You arent done yet, grasshopper. Zeejay will now probably walk you thru the crank sensor testing procedure. Thank HIM. He's awesome !


2007 5.7 Hemi, Ltd. QD II -
1997 ZJ, 4,0 select trac, Up country, track lok.
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post #62 of 81 Old 09-01-2013, 07:48 PM Thread Starter
JBrady5555
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So why would crank sensor make the fuel pump not work?
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post #63 of 81 Old 09-01-2013, 07:57 PM
Oldfrog
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Switch "ON": ( engine not running):

Open loop mode. PCM prepositions IAC motor based upon engine coolant temp. Gets info from MAP sensor, intake air temp, and TPS input. It activates auto shutdown relay, which activates fuel pump relay for 3 seconds unless engine is cranked. If engine doesnt crank, fuel pump relay ( via autoshutdown relay) is shut off.

At start up:
The computer gets info from the crank sensor, TPS, battery voltage, cam sensor, engine coolant sensor, IAT and Map. Based on those inputs, voltage is applied to the injectors.

2007 5.7 Hemi, Ltd. QD II -
1997 ZJ, 4,0 select trac, Up country, track lok.
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post #64 of 81 Old 09-01-2013, 08:04 PM
Oldfrog
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The TPS, Map sensor and crank sensor share the same 5 volt supply feed. If one of those pulls that 5 volts down to ground, then it affects all three.

2007 5.7 Hemi, Ltd. QD II -
1997 ZJ, 4,0 select trac, Up country, track lok.
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post #65 of 81 Old 09-01-2013, 08:15 PM Thread Starter
JBrady5555
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Awesome thanks
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post #66 of 81 Old 09-01-2013, 08:30 PM
ZeeJay1997
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Go ahead and order a Mopar crank sensor.

IMO, no other testing is necessary.

If you just want to hone your meter using skills, here's the test.

If it reads between 0 and 10k ohms, its bad.


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post #67 of 81 Old 09-01-2013, 08:35 PM Thread Starter
JBrady5555
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Quote:
Originally Posted by ZeeJay1997 View Post
Go ahead and order a Mopar crank sensor.

IMO, no other testing is necessary.

If you just want to hone your meter using skills, here's the test.

If it reads between 0 and 10k ohms, its bad.
Ok gonna order the molar sensor, any tricks I need to know for removal and installation?
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post #68 of 81 Old 09-01-2013, 08:38 PM
ZeeJay1997
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it's strange that you zapped your crank sensor by shorting the battery posts. I was expecting the PCM to be zapped. You may not be out of the woods yet, but you're not even going to be on the trail with a shorted crank sensor.


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post #69 of 81 Old 09-01-2013, 08:43 PM
ZeeJay1997
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Quote:
Originally Posted by JBrady5555 View Post
any tricks I need to know for removal and installation?
you'll need a lot of patience, I changed mine out several years ago and all I remeber about was that I made up some cuss words, used a long 1/4 extension, a taped up swivel, and a 10mm socket from underneath the vehicle. It helps to have someone up top to help keep the the tools on the bolt.

The sensor will come with a felt tip on the end. leave it on there and push the sensor in as tight as you can with one finger, then tighten the bolt.


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post #70 of 81 Old 09-01-2013, 08:50 PM
Oldfrog
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I hope you have small hands....because it's a biotch unless you want to remove that dang ....TV ? ..cable. I think I used a LONG extension AND another 10 inch extension with a taped up wobble joint. Came up from the back of the tranny, as I recall.


Unless you want to perform this task again, get ONLY a Mopar CPS. Dont try to save $ by using an aftermarket sensor.

2007 5.7 Hemi, Ltd. QD II -
1997 ZJ, 4,0 select trac, Up country, track lok.
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post #71 of 81 Old 09-01-2013, 09:04 PM
ZeeJay1997
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And also, be sure the switch is off and disconnect the battery now While you have it disconnected, clean the two grounds on the side of the block that Oldfrog was telling you about earlier. They are critical to your fuel/ignition system.


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post #72 of 81 Old 09-02-2013, 01:40 PM Thread Starter
JBrady5555
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Does it have to be mopar? Advanced only has bwd in stock.
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post #73 of 81 Old 09-02-2013, 01:58 PM
Oldfrog
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Yes. It HAS to be Mopar....or you'll be removing it and doing it again a day later.

2007 5.7 Hemi, Ltd. QD II -
1997 ZJ, 4,0 select trac, Up country, track lok.
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post #74 of 81 Old 09-02-2013, 03:12 PM
ZeeJay1997
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call the dealership and price one. this is the part number you need

There are other mopar retailers online but I cant attest to their service.

I've been running a Sorenson from NAPA for a few years with no problems, but i could have had a Mopar for the same price.


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post #75 of 81 Old 09-02-2013, 03:33 PM Thread Starter
JBrady5555
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Mopar it is, thanks guys
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