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  #1  
Old June 11th, 2019, 20:39
XJIron XJIron is offline
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XJ Wrong PCM replacement? No spark

New to the forum and the world of Jeeps. I recently purchased a 2000 XJ, 4.0, Auto Trans that was missing the ECU/PCM. I purchased a used ECU (P56041 638AD) online and plugged it in. Where the original one is missing I am not sure how to figure out which one I should have in there and this may be the cause for all of this. If anyone knows a way that I can figure that out please do. When I turn the key the fuel pump primes, the starter will crank, but engine does not turn over. I pulled the coil rail off and checked for spark by putting a spark plug in and grounding the spark plug. I have no spark. IT seems the CPS is a common point of failure so I checked pins "B" and "C" i get minimal resistance (4.5 I think) so I think it is good. The cluster back lights work but none of the gauges move. I have pushed and held the trip reset while turning key to on and the gauges all do there happy dance. I am also getting the dreaded "No Bus" error on the odometer after 30 seconds. The Engine only has 132,000 so I think this old girl should have plenty of life left in her.....
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  #2  
Old June 11th, 2019, 21:48
lawsoncl lawsoncl is offline
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Re: XJ Wrong PCM replacement? No spark

Googling that part number says it's for a Grand Cherokee. Going by this test, I think the CPS is bad. https://www.cherokeeforum.com/f51/testing-cps-5563/. Do you have 5-volts to the sensor?



Does the no-bus error go away if you disconnect the CPS? A bad clockspring can also cause issues if it's shorting 12volts to the bus.
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  #3  
Old June 12th, 2019, 03:19
RCP Phx RCP Phx is offline
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Re: XJ Wrong PCM replacement? No spark

It's definitely a GC computer, will it work I don't know. The GC also doesn't use the AW4 trans so who knows what else is different.
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  #4  
Old June 12th, 2019, 04:50
XJIron XJIron is offline
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XJ Wrong PCM replacement? No spark

Okay thank you. Any idea how to tell if I need an "AD","AF,
Or "??" computer without having the original one? I think I am going to pick up a CPS as well. From the forum it sounds like I should keep a spare in the glove compartment.

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  #5  
Old June 12th, 2019, 05:50
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sidewaysstarion sidewaysstarion is offline
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Re: XJ Wrong PCM replacement? No spark

That PCM isn't going to work for you, you're getting the no bus error because the Grand Cherokee has a PCI network and no CCD network, the gauge data is bused over the CCD bus.

Since you already mentioned it's an automatic, you have two choices for a PCM. P56041634AG which is for a Federal emissions and a P56041635AJ which is for CA emissions. As for the last two letters of the part number, that just signifies the version of software running on the PCM, the higher letter, the newer the software.
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I seem to have run out of self tapping washers
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Old June 12th, 2019, 07:26
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Tim_MN Tim_MN is offline
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Re: XJ Wrong PCM replacement? No spark

As stated already, you just need the correct ECU/PCM part number, the last two letters are the software revision code, and can be ignored.
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Old June 12th, 2019, 09:23
RCP Phx RCP Phx is offline
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Re: XJ Wrong PCM replacement? No spark

I have 2 2000 XJ's , they are both identical "Federal" emissions automatics. I have four ECU's 2-634AE's, 1-634AF, and one that was custom tuned so I don't know what it started life as.
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Old June 12th, 2019, 09:41
RCP Phx RCP Phx is offline
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Re: XJ Wrong PCM replacement? No spark

I forgot say that the VIN is stored in the ECU so you will need it programmed in if you don't order up a new one. I have been using....
https://www.fs1inc.com/jeep-ecu-ecm-...l=176&year=133
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Old June 12th, 2019, 10:09
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Tim_MN Tim_MN is offline
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Re: XJ Wrong PCM replacement? No spark

Having the VIN flashed into a replacement ECU is only necessary if local Smog Inspections check for it. An ECU with the correct part number will run properly without being re-flashed.
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Quote:
Originally Posted by bimmerjeeper

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Tim MAY be 100% correct, but why would a person automatically pick him as the expert .....
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  #10  
Old June 12th, 2019, 10:57
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sidewaysstarion sidewaysstarion is offline
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Re: XJ Wrong PCM replacement? No spark

Quote:
Originally Posted by Tim_MN View Post
Having the VIN flashed into a replacement ECU is only necessary if local Smog Inspections check for it. An ECU with the correct part number will run properly without being re-flashed.
Unless it is equipped with the Sentry Key Immobilizer System(SKIM), then if the VIN isn't set the vehicle will only run for ~3 seconds.
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Originally Posted by cracker
I seem to have run out of self tapping washers
99 4.0/AW4/231, with a few basic bolt ons.

Click here to support
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  #11  
Old June 12th, 2019, 14:17
XJIron XJIron is offline
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XJ Wrong PCM replacement? No spark

Pretty sure this started out in the great North East so don't think it would have CA emissions. Time to order some parts. I will update as thing progress. thanks for the help everyone. I hate to see the old girl just sitting like this. Not gonna give up.

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  #12  
Old June 12th, 2019, 14:59
alwayzAMC alwayzAMC is offline
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Re: XJ Wrong PCM replacement? No spark

where in maine are you ? i have an extra 2k computer kicking around . i am in central maine. i am not sure if it is a cali or federal, it has the 2 pre cats. i think that makes it a cali, but not sure. also have extra odometers if you need it, but most of the time the nobus can be fixed by cleaning the contact points on yours.
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  #13  
Old June 12th, 2019, 19:16
Heavyopp Heavyopp is offline
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Re: XJ Wrong PCM replacement? No spark

2 pre-cats makes it a Cali emission vehicle
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  #14  
Old June 13th, 2019, 11:15
XJIron XJIron is offline
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XJ Wrong PCM replacement? No spark

I should have checked here first. I am in the Portland area. I picked up a replacement PCM online. Should be here soon.

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  #15  
Old June 16th, 2019, 15:21
XJIron XJIron is offline
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XJ Wrong PCM replacement? No spark

Well I got the new PCM and CPS installed and cleaned up the pins on the gauge cluster. No more BUS error and the gauge work, but it still does not start. I can hear the pump prime and smell the gas. I pulled the air box off and sprayed some starter spray hoping it would turn over for a few seconds but no go. I am guessing still not spark. To top it all off my wife washed the pants I had the title in and I have not transferred it yet. FML. Two steps forward one step back. Any other common things that go and cause no spark?

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