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  #16  
Old June 16th, 2019, 15:54
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Tim_MN Tim_MN is offline
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Re: XJ Wrong PCM replacement? No spark

Genuine Jeep CPS or a cheap crappy Chinese clone part ?

It is likely that the PCM has no adaptive data stored in memory due to extended storage and you will have to feather the gas pedal to start the engine, and continue until the idle speed becomes steady. If you do not have success fairly quickly you will need to follow the troubleshooting below.


For 1996+ Jeeps, the OBD-II engine computer (ECU/PCM) re-boots, and the idle settings are deleted, when you: (1) let the battery run down by leaving the lights or radio on, (2) disconnect the battery for an extended period of time, (3) when the battery goes bad and needs replacing, (4) when the alternator is not properly charging the battery, (5) or when poor battery connections result in a voltage drop at the PCM or poor battery charging. Loose, corroded, or damaged battery cables or ground wires may also cause or contribute to the problem. A faulty Coolant Temperature Sensor may also cause similar symptoms. Testing of the CTS is recommended as part of the diagnostics. A poor ground at the ignition coil can also cause similar symptoms.

The reboot symptoms are: (1) having difficulties starting the engine without depressing the gas pedal, and (2) the engine will have a low idle and probably stall unless you keep your foot on the gas pedal. (3) The ECU will relearn the idle settings after a short period of driving and the engine will sometimes start and idle normally.

Begin with basic trouble shooting of the start and charge systems. Remove, clean, and firmly reconnect all the wires and cables to the battery, starter, and alternator. Look for corroded or damaged cables or connectors and replace as needed. Copper wires should be copper color, not black or green. Do the same for the grounding wires from the starter to engine block, the ground wires at the coil, and the ground wires from the battery and engine to the Jeep's frame/body. You must remove, scrape, and clean until shiny, the cable/wire ends, and whatever they bolt to. Jeeps do not tolerate low voltage, bad connections, or poor grounds.
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Quote:
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Go ahead and slam the liftgate down on a blanket, and see how long you are laughing.
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Tim MAY be 100% correct, but why would a person automatically pick him as the expert .....

Last edited by Tim_MN; June 16th, 2019 at 16:30.
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  #17  
Old June 16th, 2019, 16:08
XJIron XJIron is offline
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XJ Wrong PCM replacement? No spark

Ok wow. Lot of info there thank you. I purchased a used OEM PCM from the same year and I do not have an I mobilizer on it as far as I can tell. When I bought it the negative terminal was corodid so I should check the other grounds and the CTS. Thanks again

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  #18  
Old June 17th, 2019, 06:44
Heavyopp Heavyopp is offline
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Re: XJ Wrong PCM replacement? No spark

Search on how to check coil rail -- easier if you watch a video

Better check your fuel pump pressure -- Might be able to get a loaner gauge at one of the auto parts stores -- I believe its 49 PSI at the rail you are looking for

Have you pulled any spark plugs to see what condition they are in?
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  #19  
Old June 21st, 2019, 19:06
XJIron XJIron is offline
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XJ Wrong PCM replacement? No spark

Okay so I cleaned all the grounds and checked fuel pressure at the rail and it is about 45 PSI. I did also get a Bluetooth OBD2 and installed torque. I get the two error codes in the photo. I see one may be the TPS sensor so I cleaned it's ground with no luck. Maybe the sensor? I am not sure what the other code means but I still don't have spark. Not sure if it is the rail or something before the ignition rail.

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  #20  
Old June 21st, 2019, 19:38
Heavyopp Heavyopp is offline
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Re: XJ Wrong PCM replacement? No spark

Is there a relay in place in the PDC for the ASD position?
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  #21  
Old June 21st, 2019, 19:53
XJIron XJIron is offline
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XJ Wrong PCM replacement? No spark

Yes on both the ASD and ASD relay fuse

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  #22  
Old June 22nd, 2019, 06:01
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Re: XJ Wrong PCM replacement? No spark

Use the OBD-II trouble codes to guide your diagnostics and sensor testing.

A simple Google search discovers this:


P0122 JEEP - Throttle Position Sensor/Accelerator Position Pedal Circuit Low Input

Possible causes
•Faulty throttle position sensor
•Throttle position sensor harness is open or shorted
•Throttle position sensor circuit poor electrical connection
•Faulty Powertrain Control Module (PCM)



P1694 JEEP - No Messages Received From The Powertrain Control Module

Possible causes
•CCD Bus (-) circuit open between Powertrain Control Module (PCM) and Transmission Control Module (TCM)
•CCD Bus (+) circuit open between PCM and TCM
•Transmission CCD bus wiring damaged
•Faulty TCM
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Quote:
Originally Posted by bimmerjeeper

Go ahead and slam the liftgate down on a blanket, and see how long you are laughing.
Quote:
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Tim MAY be 100% correct, but why would a person automatically pick him as the expert .....
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  #23  
Old June 27th, 2019, 18:05
XJIron XJIron is offline
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XJ Wrong PCM replacement? No spark

I feel like I am chasing my tail here.....or maybe making headway. Not sure. I have been able to get rid of the last two fault code by replacing a couple of parts thanks to everyone's help. However now I have a new code. Not sure if fixing the last codes allows the computer to see a new faulty sensor or not. I have a replacement camshaft position sensor on the way as that is the new error code. Could this be because the Jeep was sitting for two years or am I just chasing my tail here?

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  #24  
Old June 27th, 2019, 18:35
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Re: XJ Wrong PCM replacement? No spark

A possibility is you have a sensor on the 5 V supply tree (orange wire) that has low resistance or is partially shorted. If the 5 V orange wire supply voltage is low it can cause a bus error.

One way to check (low tech) is to hook up a voltmeter to the orange wire at a good easily accessible position and unplug the sensors on the 5 V orange wire tree. I'd start with the sync (cam position sensor) then the TPS, then the MAP and then the oil pressure sensor, When the right sensor is unplugged the voltage in the 5 volt supply will come back up and hopefully, the bus error will disappear.

Check that the wires for the oil pressure sensor aren't chaffed and/or contacting ground, a known trouble spot.

I had a CPS that tested good but wasn't, it was sucking down the voltage in the 5 V supply orange wire tree. On a hunch I unplugged the CPS and my bus came back. Could be another sensor doing the same thing.

I'd check the cheap stuff before I'd do the expensive stuff. My standard troubleshooting routine is to test easy then hard, cheap then expensive.
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  #25  
Old June 28th, 2019, 03:54
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Tim_MN Tim_MN is offline
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Re: XJ Wrong PCM replacement? No spark

I agree that probing for 5 volts at all the OBD sensor is a good starting point. Physically look for wire harness damage and wire plug damage and consider that there may be one or more faulty wire splices.


P0340 JEEP - Camshaft Position Sensor

P0340 Jeep Possible Causes:
•Faulty Camshaft Position Sensor
•Camshaft Position Sensor wire harness is open or shorted
•Camshaft Position Sensor wire plug poor electrical connection
•Faulty starter motor
•Starting system circuit
•Dead (Weak) battery

P0340 Jeep Tech Notes:
Sometimes and in some models, low battery voltage or a weak starter can trigger a Camshaft Position Sensor code.
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Quote:
Originally Posted by bimmerjeeper

Go ahead and slam the liftgate down on a blanket, and see how long you are laughing.
Quote:
Originally Posted by soyjer

Tim MAY be 100% correct, but why would a person automatically pick him as the expert .....
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  #26  
Old June 28th, 2019, 20:31
XJIron XJIron is offline
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XJ Wrong PCM replacement? No spark

Okay thanks guys. I have a new camshaft position sensor on its way and should be here mid next week. I will check to make sure the wires are not all jacked us as well, that doesn't cost a dime so that is easy. I think I need to find a local junkyard that I can get spare parts at for this thing. LOL

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  #27  
Old June 29th, 2019, 06:32
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Re: XJ Wrong PCM replacement? No spark

All three of my Cherokees carry a spare Crank and Cam sensor.
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Quote:
Originally Posted by bimmerjeeper

Go ahead and slam the liftgate down on a blanket, and see how long you are laughing.
Quote:
Originally Posted by soyjer

Tim MAY be 100% correct, but why would a person automatically pick him as the expert .....
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  #28  
Old July 10th, 2019, 15:08
XJIron XJIron is offline
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XJ Wrong PCM replacement? No spark

Okay so my Bluetooth obd2 died on me but I have a new one now. I changed both the cam shaft and crank shaft sensors and I am still getting the P0340 error. I am getting my self a bit confused though. Which sensor should I be looking for 5volts on?

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  #29  
Old July 10th, 2019, 16:44
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Tim_MN Tim_MN is offline
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Re: XJ Wrong PCM replacement? No spark

All of the OBD-II engine control sensors are 5 volts.
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Quote:
Originally Posted by bimmerjeeper

Go ahead and slam the liftgate down on a blanket, and see how long you are laughing.
Quote:
Originally Posted by soyjer

Tim MAY be 100% correct, but why would a person automatically pick him as the expert .....
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  #30  
Old July 10th, 2019, 16:52
XJIron XJIron is offline
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XJ Wrong PCM replacement? No spark

Well that makes it easy. Thanks.

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