1998 XJ 4.0L 4WD ECU/ECM wiring/Electric diagram - JeepForum.com
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post #1 of 5 Old 02-13-2020, 12:21 PM Thread Starter
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1995 XJ Cherokee 
Join Date: Apr 2010
Location: Las Vegas
Posts: 31
Xj 1998 XJ 4.0L 4WD ECU/ECM wiring/Electric diagram

I'v been doing some searching, possibly ♫♩ in all the wrong places ♪♫, and cannot find a diagram for the ECU/ECM for my Jeep.

The goal is to see if one can be scratch-built. I know that in another forum,
for Subaru, one user had made on using a Rasberry Pi. I'm looking to go a little more caveman and scratch-build a unit with ports and variable components for programming/tinkering that I can harness into the factory slot. I want to build an analog interface in the cabin to adjust on the fly.

At the very least, I need a detailed diagram (as in chip numbers for various modules or contents of modules) so that I know what components to search for and to build an initial unit with decent room for probing while in use.

Any ideas where to get one, or does someone have one they'd be willing to share or point me towards?

Thank you.

1988 XJ [5 yrs] Stolen
1995 XJ [17 yrs] Totaled by an 4$$-hat. RIP
1998 XJ [New!]
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post #2 of 5 Old 02-13-2020, 07:17 PM
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2000 XJ Cherokee 
Join Date: Apr 2002
Location: out in the garage - Minneapolis
Posts: 29,067
I would say that you are looking for closed-source proprietary software, non-free computer software for which Jeep retains intellectual property rights. You may be able to obtain a PCM and reverse engineer the software, and the components, but I doubt you will have much luck finding anybody with that info to share for free.

There are a few people that can reprogram some of the PCM parameters to make use of engine modifications.

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post #3 of 5 Old 02-14-2020, 12:09 AM
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2004 WJ 
Join Date: Jul 2013
Location: bakersfield
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Doubt you will find a detailed diagram anywhere. Although there might be some options to explore if you have time to invest in it. Option 1, you could look into getting a used PCM from a junkyard and use it as a donor. Tear it apart, find out which component contains the programming (I imagine some type of ROM) desolder and swap with socket mounted flash chip. Option 2, you could see if they make blank PCMs that would be compatible. Either way you're going to have to figure what to flash it with... Option 3 is the Pi-like setup which is really an emulator. That would likely be the only option that can be tweaked in real time.

Find the FSM for your year model to get the PCM connectors pinout. That might be really helpful at some point.

04 WJ 4.0 - Avital 4103, DB-ALL
91 XJ 4.0 - Avital 4103, Stage-2 aFe intake system, BBK high flow Throttle Body, 703s injectors, Jones Exhaust A3518M-5

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post #4 of 5 Old 02-14-2020, 10:57 AM Thread Starter
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1995 XJ Cherokee 
Join Date: Apr 2010
Location: Las Vegas
Posts: 31
So, if there are people that can reprogram these things then they must have access to the software, either on it or something that they created to do the job. It's my understanding that these are flashed like you would for firmware updates on other devices. I would have thought that any relevant patents for XJs, which software of this type falls under, by its structure and method of use, should have expired by now. Design is 14yrs, utility is 17yrs and industry is no longer than 20yrs max from filing. My Jeep can go drinking.

In any case, I'm hoping that someone with some programming knowledge or experience with these, or even wiring to bypass, can give me a lead or a starting point.

1988 XJ [5 yrs] Stolen
1995 XJ [17 yrs] Totaled by an 4$$-hat. RIP
1998 XJ [New!]
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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post #5 of 5 Old 02-19-2020, 07:36 PM
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1997 XJ Cherokee 
Join Date: Dec 2013
Posts: 68
read the 2nd page of posts, thankfully the original poster posted links on imgur..good man!
all 3 pcm connectors w/descriptions.
I printed these out without any reason to, now I have an IAC issue, thanks again to the original poster five-string.
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diagram , diy , ecm , ecu , wiring

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