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2000 XJ Engine Issues

Better_than_Tom

NAXJA Forum User
Location
Corona
I have a 2000 XJ. I bought it was a motor that had been supposedly rebuilt about 20k ago. Long story short the car has been in the shop since November. The mechanic is havng trouble finding the problem so Im hoping to get some pointers. The engine has low idle when its cold outside and it misfires and it gets worse as the RPMs raise.

According to the mechanic one of the spark plugs is being told to fire twice by the computer. He replaced the computer and the coil pack. The car throws a couple codes one of them being P0391 I believe.

When I bought the car the sensor on the side of the motor(i believe thats the camshaft sensor), which is normally parallel with the motor was cocked off about 60 degrees. When you set it to the factory position the motor barely runs. Cam and crank sensors have both been replaced with OEM sensors. Im thinking that the cam possibly has a flat spot...any other ideas would be greatly appreciated.

THANKS FOR READING!!!
 
Your mechanic is the child of first cousins, and a mouth breathing Moron. A 2000-01 distributor-less ignition 4.0L is a waste spark system. The cylinders are paired up, and each spark plug fires twice during the combustion cycle, every time, and all the time.

You need to know exactly, by the number, all the Check Engine Light trouble codes to begin diagnostics. Randomly throwing new parts at a problem is the sign of an incompetent mechanic.

Figure out why the distributor-less cam sensor was not correctly oriented. Go here and read the info. http://jeep.blackonyx.net/pdfs/jcss.pdf . Find a mechanic that can read without moving his lips and ask him to synchronize the cam sensor.

P0391 is not a valid Jeep trouble code. If you mean P1391 that would tend to confirm the cam sensor synchronization being wrong.

P1391

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) Misfires and bucking of the engine.
(3) 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.
 
Your mechanic is the child of first cousins, and a mouth breathing Moron. A 2000-01 distributor-less ignition 4.0L is a waste spark system. The cylinders are paired up, and each spark plug fires twice during the combustion cycle, every time, and all the time.

You need to know exactly, by the number, all the Check Engine Light trouble codes to begin diagnostics. Randomly throwing new parts at a problem is the sign of an incompetent mechanic.

Figure out why the distributor-less cam sensor was not correctly oriented. Go here and read the info. http://jeep.blackonyx.net/pdfs/jcss.pdf . Find a mechanic that can read without moving his lips and ask him to synchronize the cam sensor.

P0391 is not a valid Jeep trouble code. If you mean P1391 that would tend to confirm the cam sensor synchronization being wrong.

P1391

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) Misfires and bucking of the engine.
(3) 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.

Im sorry about the code it is a P1391. He hooked up the engine too an oscilloscope and the coilpack from 3 and 4 was doin the suppossed misfire. He re-indexed the cam sensor and nothing. He then replaced the timing chain as well thinking that it may be stretched and no change. He said something about when he did the timing that the cam marks would only like up on the exhaust stroke(not sure if that makes sense Im not a motor expert) and he said that wasnt normal. After talking to a few motor shops he said that the timing on jeeps is opposite of most cars, can anyone confirm or deny this?

If I pay to have a wiring harness change Im looking at a hefty bill and I want to make sure thats the problem. As I said I kinda suspect the cam but dont know for sure.
 
Anybody that can use a computer, and has a credit card, can subscribe to ALLDATA Factory Service Manuals or can download a genuine Jeep Factory Service Manual (FSM).

ALLDATA is the leading provider of manufacturers original Factory Service diagnostic manuals, repair manuals, and information to the professional automotive service and collision industries.

Your mechanic may be a nice guy, and trying hard to fix your Jeep, but I don't think he is very bright or very skilled. YMMV. Indexing the engine, installing a cam sensor or distributor, and then checking the work is step by step explained in the FSM. I suggest a more Jeep skilled mechanic or simply a more competent mechanic.
 
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