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Unread 12-16-2012, 10:10 PM   #1
86mcss
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98 cherokee xj stumbles at 2000 to 2500 rpm

Ok here goes *long sigh*

I bought a 98 xj (4.0, auto, 4x4) for a couple hundred bucks with a blown motor. I rebuilt the entire motor (bored .020 over). It has new plugs, wires, distributor cap, cam sensor, crank sensor, and map sensor.

On first attempted start up it would not start. I had to crank it a couple of times for her to fire. Once she fired up she idled pretty good just sitting there but I found out that if you try to take her above 2000 rpm she would back fire through the exhaust.

So I turned her off and tried turning her on again and same thing. She was hard to start but would start eventually. This time though the check engine light came on for code p1391 and p0320. Odd I thought since it has a new crank sensor and cam sensor already. So I checked both sensor plugs and cleaned them both out. Also checked fuel pressure during this time and it was a good 50psi at the rail. I then removed the crank sensor and cleaned it off as well. I reinstalled the crank sensor and tried to fire her up again and the same thing. Hard to start and the same two engine codes came back on.

At that point I went to the local dodge dealership and bought another crankshaft position sensor along with the paper spacer. I went home and installed another new crankshaft position sensor.

I got her to start up a little bit better but the same codes came back on, p1391 and p0320.

At this point I checked the wiring harness that lead to both sensors and everything was good.

Fast forward to the next weekend and I borrowed a scan tool from a friend. I checked the engine while it was running and it had no misfires and everything ran great according to the scan tool.
-both O2 sensors were functional and working good
-TPS was reading accurate
-timing was advancing correctly
-crankshaft sensor was reading
-camshaft sensor was reading

...the only thing that was off to me were the camshaft counts and the crankshaft counts according to the scan tool.

my camshaft counts would never go above 60 or so and my crankshaft counts would go above 200 (while revving the engine)....I thought the camshaft counts would be higher than my crankshaft counts? correct?

Anyone have any ideas to throw my way? I am at a loss of what to check next. And please forgive me if I left out any details...just ask and I will answer any and all questions.



this is how she looked the day i bought her


this is how she looks now


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Unread 12-17-2012, 03:03 AM   #2
bigbill888
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check ignition coil
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Unread 12-17-2012, 06:37 AM   #3
CJ7-Tim
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If you borrowed a DRB-III scan tool, synchronize the cam sensor. The timing chain is probably stretched.

Google this -> scan tools, o'scopes and toothpicks.

P0320 - No RPM Signal to PCM (Crankshaft Position Sensor Signal to JTEC) A CKP signal has not been detected at the PCM.

P1391 Intermittent Loss of CMP or CKP Signal. Loss of the Cam Position Sensor or Crank Position sensor signal has occurred.

P1391 – Possible symptoms:

(1) random misfire/stumble/stalling, often over bumps or right turns and when going into reverse.
(2) shorted out the Fuel pump/ECU power wire.


Partial Fix: Replace corroded ground wires/connectors and clean ground wire connection points.


Fix #1:

Inspect your wire harnesses for damaged wires, chafed insulation, or failed wire splices. Use a volts/ohms multi-meter to check the resistance of the ground wire circuits from each sensor.

Fix #2:

Timing may off. Re-index the distributor per the FSM instructions, or replace faulty distributor.


A mis-indexed distributor may exhibit surging, light bucking or intermittent engine misfiring. This will most likely occur when the vehicle is at operating temperature and under a light load at approximately 2,000 rpm. This condition may be caused by a mis-indexed distributor.

The factory procedure must be used as outlined in the service manual. Some of these may be indexed with a scan tool, while others require the use of a volt meter to verify position.
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Unread 12-17-2012, 11:23 AM   #4
86mcss
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Quote:
Originally Posted by bigbill888 View Post
check ignition coil
has been checked out and is good. thank you

Quote:
Originally Posted by CJ7-Tim View Post
If you borrowed a DRB-III scan tool, synchronize the cam sensor. The timing chain is probably stretched.

Google this -> scan tools, o'scopes and toothpicks.

P0320 - No RPM Signal to PCM (Crankshaft Position Sensor Signal to JTEC) A CKP signal has not been detected at the PCM.

P1391 Intermittent Loss of CMP or CKP Signal. Loss of the Cam Position Sensor or Crank Position sensor signal has occurred.

P1391 – Possible symptoms:

(1) random misfire/stumble/stalling, often over bumps or right turns and when going into reverse.
(2) shorted out the Fuel pump/ECU power wire.


Partial Fix: Replace corroded ground wires/connectors and clean ground wire connection points.


Fix #1:

Inspect your wire harnesses for damaged wires, chafed insulation, or failed wire splices. Use a volts/ohms multi-meter to check the resistance of the ground wire circuits from each sensor.

Fix #2:

Timing may off. Re-index the distributor per the FSM instructions, or replace faulty distributor.


A mis-indexed distributor may exhibit surging, light bucking or intermittent engine misfiring. This will most likely occur when the vehicle is at operating temperature and under a light load at approximately 2,000 rpm. This condition may be caused by a mis-indexed distributor.

The factory procedure must be used as outlined in the service manual. Some of these may be indexed with a scan tool, while others require the use of a volt meter to verify position.
I did not synchronize the cam sensor with the scan tool. I will do that the first chance I get. Thanks for that.

I will google what you suggested as well and read up on it.

...motor has brand new timing chain. the motor is a complete fresh rebuild. everything on it is new (timing chain, lifters, oil pump, cam, water pump, yadda, yadda yadda).

checked and removed distributor 3 different times to assure it was installed properly and according to factory specs.

grounds have been checked and all are good. I even added an extra ground because i felt it was lacking enough grounds.

thanks for the replies guy.
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Unread 12-21-2012, 05:26 PM   #5
86mcss
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the wiring harness had a couple bad spots in it. i had to take an OHM meter to it and find which wires and fix accordingly.

it sucks it had to be something like that but the jeep runs perfect now and will serve as my new daily driver

thanks for the help guys i really appreciate it.
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Unread 12-21-2012, 06:08 PM   #6
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You need to give CJ7 TIM a big thumbs up + 500$ gift card to his fav. Vendor LOL
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Unread 12-21-2012, 06:28 PM   #7
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Originally Posted by buildin1XJ View Post
You need to give CJ7 TIM a big thumbs up + 500$ gift card to his fav. Vendor LOL

i have 500 doll hairs for him right here...just need his address.
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Unread 07-17-2013, 07:51 PM   #8
bigb229
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Help!

Tried to pm you but your box is full. I'm having the same issues but can't track it down. Where exactly did you find the wiring problem! Thanks!
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Unread 07-17-2013, 09:11 PM   #9
86mcss
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Tried to pm you but your box is full. I'm having the same issues but can't track it down. Where exactly did you find the wiring problem! Thanks!
it was the actual wire coming off of the crankshaft position sensor. the wire was brittle and had broken inside the wiring harness. i replaced most the wire because a lot of it was brittle and was not good.

if your wiring is good i am willing to bet your distributor is not installed correctly.
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Unread 07-17-2013, 09:27 PM   #10
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I'll have to check it. I've indexed that distributor every way possible.
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