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Unread 09-14-2012, 11:22 PM   #1
GetLifted
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p1391 Crank Position Sensor and Cam Sensor info needed

Symptoms:

Code p1391 like clockwork over 2500 RPM or over 50% throttle. I reset the code, drove around, went to smog guy told him to keep it under 2000 rpm and it passed.

I drive out, give it 50% throttle or more and misfire + CEL.

It used to happen when it got hot only, now it happens when it warms up, gets turned off, allowed to cool till next day, and then restarted. When it misfires on a cold restart though i only feel it for the first stomp on the pedal. After that it seems to clear up until it warms up. But if i give it a good load 2 starts in a row the p1391 comes up.

Diagnostic:
A month ago the symptoms got bad. I had a cracked coil and unknowingly replaced it with a bad autozone coil. This led me to replace a LOT of other parts. Subsequently my entire ignition system, injectors, TPS, o2s etc...are brand new OEM or better.

I have begun back probing all my sensors to check for readings within specs.

-Cam PS seems to be in order. 5.18v in feed and when bumped into position the output to PCM shows the same.

-Crank Position Sensor seems funky. On harness side of connector the Purple/white stripe is 5.18v with key on grounded to the middle black/blue stripe. And when bumped into position the grey/black stripe is 5.18V when grounded to the middle black/blue stripe wire. BUT on the other side of the connector (CPS) the MIDDLE black/white stripe has 5.18V. Isnt this supposed to be a ground? If I ground the engine harness side of the middle connector i get 0.00V but if i ground the middle wire on the CPS side I get 5.18V! Is this correct?

Am I doing this right? The resistance values are infinite on all leads 1, 2, and 3 (reads 1_______ as if the probes were in mid air).

So my questions would be: Are these readings normal? If not since i forgot to disconnect the battery when removing and installing both CPS's did I kill them? If the sensors are ok and normal can i do this:



to a 97 cherokee with a distributor?


Lastly, does anyone know where I can find a good mechanic in southern california that knows how to work on these 4.0s and knows how to use an oscilloscope?
I need this done:
http://www.askamechanic.info/askamec...nt/view/55/47/

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Unread 09-15-2012, 05:38 AM   #2
tjwalker
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P1391 is intermittent loss of either the crank sensor OR the cam sensor. The vast majority of the time, replacing the faulty sensor will resolve this problem.

You can try testing both of the sensors with the factory service manual and a meter. But test data may very well be inconclusive for a sensor that is faulty, but not dead.

In that case, you should start with replacing these sensors with MOPAR sensors from Jeep. There is a BIG difference in quality of engine management sensors. I'd start with the crank sensor as it fails more often than the cam sensor. But if that doesn't resolve it, replace the cam sensor.

Here is a thread that gives some good information on resolving the P1391 code....

http://www.naxja.org/forum/showthread.php?t=931357
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Unread 09-15-2012, 06:35 AM   #3
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Oh i know what 1391 is. I have replaced both sensors as well as the distributor. I have also tested both. I have done more searching then one can do (read that link posted, have it saved on my phone already ). I need someone to answer my few questions i posted. The answers arent going to be in your link.

Can i do the toothpick trick on a 97? Are my sensors toast? Did i kill them? Does anyone know where to find a mechanic in SoCal that can use an oscilloscope? I posted test results that dont seem correct and need advise.
Thanks


Also* i have a new computer, entire ignition system, and EVERY SINGLE SENSOR. Ignition, and fuel delivery are all new except for the pump. The pump is at 49psi and stays there when reving.

When it decides to run good it does. But too much skinny pedal and it throws a code. Need a data logging scope to find this one.
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Unread 09-15-2012, 07:09 AM   #4
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Let me mention that all parts installed are now factory chrysler except for an Accel coil.
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Unread 09-15-2012, 07:22 AM   #5
CJ7-Tim
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A code does not always indicate a faulty part or sensor. If you are having wire harness issues or have corroded wire connectors, the ECU thinks that no data is the same as a faulty sensor. Inspect your wire harnesses for pinched wires, chafed insulation, mising/bent crushed wire plug pins, and failed wire splices.

A P13191 can be a faulty sensor, or a distributor that is not correctly indexed.

Use genuine Jeep sensors.
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Unread 09-15-2012, 09:28 AM   #6
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I tested the sensors and posted results. Can someone read those and comment please?

I am going out to check the distributor index.
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Unread 09-15-2012, 10:58 AM   #7
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Dizzy is indexed, good to go.

*Made 17 calls to all local mechanics open today. Only found ONE that owns and knows how to use an oscilloscope. The place is called Budget Transmissions in San Bernardino. He told me "what we can do is hook up the scope and you drive us around until it triggers the code" thats what i wanted to hear! He can look at it monday. So i guess ill wait.


Side note i cant f*****g believe how many shady freakin mechanics there are out there (~10/17) that told me "scopes are useless" "we dont use those tools we have better ones like OBD scanners" "oh that year/car/engine is hard to work on/has many problems" "bring it down i fix everything" 1/4 didnt even speak english.
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Unread 09-15-2012, 05:07 PM   #8
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GOOGLE - SCAN TOOLS, O-SCOPES AND TOOTHPICKS

Print it out and give to the mechanic.
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Unread 09-15-2012, 07:52 PM   #9
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You mean the link i posted in the original post?

Im gonna have it scoped and ill report back.
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Unread 09-15-2012, 08:02 PM   #10
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Read it all, missed the link hiding at the end.
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Unread 09-15-2012, 08:09 PM   #11
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I was just giving you a hard time

But do you know if a 96 with a dizzy has a hole to align with a toothpick like a distributor-less 2000 does? I dont remember if it had the holes?
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Unread 09-16-2012, 05:36 PM   #12
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While i have been waiting i just wanted to go over a checklist on what else to look at.

Check for stretched timing chain: visually, or take dizzy cap off and rotate crank with a wrench. Look for the crank to move before the rotor.

Check flywheel: remove starter, a few bolts, then remove flywheel inspection plate and check for cracks and loose bolts
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Unread 09-17-2012, 09:55 AM   #13
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More references:
This is exactly what mine did (minus the engine swap)
http://www.cherokeeforum.com/f2/cold...e-4-0-a-23233/



Just double checked timing chain, its tight. On to the mechanic to scope it. Cant believe i have not found one updated thread with a fix.
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Unread 09-18-2012, 07:58 PM   #14
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p1391 code, misfires, PCM RPM signal lost, all due to a faulty wire harness on BOTH my jeep (female harness loose not grabbing male side of cam sensor pin), AND my cheap autozone cam sensor harness having a crimped male pin in it making the problem worse after the new dizzy.

After months of this diagnosing and $$$$$....a 1.25$ cut harness from the junkyard and some solder, plus a quadruple checked re-index ....IT TRULY APPEARS FIXED

***The pin can be used on a 96/97 to line up the dizzy but it goes in vertically.
***Scanner and Scope discovered RPM signal lost, and that i was losing my 5volts into my cam sensor when the jeep got hot or under tremendous load.
***Re-Index the dizzy with the valve cover off to inspect valves during this time of bad running conditions and misfires, and to set the motor at 100% certain TDC.
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Unread 09-18-2012, 08:06 PM   #15
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I dont have a pic of the harness i cut off...i hit it with my hammer lol

Here is the autozone ****


And proof its fixed. I nearly ran it outta gas stompin it while hot





No codes no misfires
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