1986 CJ-7 258 (not 4.2L) to 4.0L (1995 Cherokee Donor) - JeepForum.com
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Unread 07-17-2015, 12:49 PM   #1
yohan1979
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Cj 1986 CJ-7 258 (not 4.2L) to 4.0L (1995 Cherokee Donor)

Hey All,

Just starting my parts list after finally acquiring a donor 4.0l (had a 42RE paired) with the plan of keeping my T176 and Dana 300. I've read just about every thread out there and I'll update as we go. However, does anyone have any horror stories to share with the overall plan, including relocating the CPS to the front with Hesco's damper kit or eliminating the AC pump from the serpentine track?

PCM-wise, I've read several threads indicating an auto PCM will be fine, but finding PCM lists has been challenging. Mopar lists P5007147 as compatible, but also suggested 56028852 as a match for the manual PCM for that model year (1995).

Looking forward to getting started and joining the CJ MPI family!

Cheers ,
Yohan


Last edited by yohan1979; 11-20-2015 at 09:39 AM.. Reason: Title said "4.2", technically the CJ inline 6 is referred to as the 258. After 1986, they are considered 4.2L.
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Unread 07-17-2015, 07:49 PM   #2
Skerr
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This is a great swap. You won't regret it. No horror stories that I know of. Some folks like the Hesco kit, and some don't. Cost was a deciding factor for me so I modified the bell housing. Wasn't really hard to do. Use the 4.0 harness and distribution box. You should be OBDI, and IMO, that was easier than OBDII. I left the disabled compressor in the loop because I didn't find other options. No problems with having done that. I swapped from an auto Cherokee as well, so found a computer from a '93 manual in the JY. Swapped it in with no issues. Figuring out the wiring was most difficult part for me. You will also need a new pilot bushing and maybe flywheel. Lots of info and support for this swap. Good luck.
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Unread 07-18-2015, 05:56 AM   #3
chucker2
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Its a great swap. alot of power. I went from iron duke 4 cyclinder. I have the weak t-5, but i dont dog it. You can use any PCM from a 91 to 95 jeep. Get the one that is for a manual. I just purchased a new rebuilt pcm from Oreillys for 100.00. I swapped in dodge neon injectors and a 1999 intake, bored the TB and it runs great. Plus a borla header and straight thru cat and exhaust. Mine does have the hesco harmonic balancer crank sensor.

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Unread 07-18-2015, 08:58 AM   #4
wijeepguy716
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You won't regret doing the swap. I did this same swap on my 86 but the help housing bolted right up with no modification needed ( t-5) . I used a auto computer and grounded the trans wire and made the mounts for the computer and pdc to mounts on the fender. The wiring wasn't bad, just get the fsm for the donor and the cj and start cutting. I saved the a/c wiring because I was going to do a onboard air system, but sold the jeep before I could do it.
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Unread 10-13-2015, 02:01 PM   #5
yohan1979
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Well we're about half-way home on the swap. The 4.0l is in and after cutting at least half of the wiring harness out, I've started toward the five to fire. I have retained the PDC, but kept my T-176 which means I've kept my 4.2 starter and solenoid. The write-ups I've found so far are a bit confusing as I think the authors assume folks are migrating to the 4.0 starter which deletes the 4.2 starter solenoid.

I ended up using the Hesco kit for the CPM which was quite easy to install, but required modification to extend sensor wires to reach the harness connector. Just wanted to leave a note for other users about that learning experience...

Plugging right along, but welcome some opinions about wiring the PDC to mate with the existing CJ dash and ignition circuits. So far, the power and ground to PDC are no-brainers and the transmission neutral sense to ground, so that's three down. Keyed power from the donor (95 XJ) PDC via which cavity to feed the main power to the CJ fuse block? And then which cavity from the PDC for the CJ blue ignition wire? And which wire from the PDC back to the CJ 4.2 starter solenoid (replaces the light blue wire)?

Lastly, there appears to be some debate about which PDC cavity to use for the fuel pump. It seems like this debate shouldn't be a debate at all and I should use the cavity that ASD controls. I'm having a hard time seeing any benefit to not having my fuel pump shut down if the computer detects trouble. Am I crazy?

EDIT: Also, the CJ brown wire that served to excite the alternator, I think, is no longer needed, but there hasn't been any mention of deleting that wire in the write-ups either.
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Unread 10-13-2015, 02:13 PM   #6
RenoF250
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Quote:
Originally Posted by yohan1979 View Post
Well we're about half-way home on the swap. The 4.0l is in and after cutting at least half of the wiring harness out, I've started toward the five to fire. I have retained the PDC, but kept my T-176 which means I've kept my 4.2 starter and solenoid. The write-ups I've found so far are a bit confusing as I think the authors assume folks are migrating to the 4.0 starter which deletes the 4.2 starter solenoid.

I ended up using the Hesco kit for the CPM which was quite easy to install, but required modification to extend sensor wires to reach the harness connector. Just wanted to leave a note for other users about that learning experience...

Plugging right along, but welcome some opinions about wiring the PDC to mate with the existing CJ dash and ignition circuits. So far, the power and ground to PDC are no-brainers and the transmission neutral sense to ground, so that's three down. Keyed power from the donor (95 XJ) PDC via which cavity to feed the main power to the CJ fuse block? And then which cavity from the PDC for the CJ blue ignition wire? And which wire from the PDC back to the CJ 4.2 starter solenoid (replaces the light blue wire)?

Lastly, there appears to be some debate about which PDC cavity to use for the fuel pump. It seems like this debate shouldn't be a debate at all and I should use the cavity that ASD controls. I'm having a hard time seeing any benefit to not having my fuel pump shut down if the computer detects trouble. Am I crazy?

EDIT: Also, the CJ brown wire that served to excite the alternator, I think, is no longer needed, but there hasn't been any mention of deleting that wire in the write-ups either.
What do you mean "cavity" - pin on the connector?

What alternator are you using? If the 4.0 alt you still need the PCM control.

I ran the factory FP relay to control the relay just keep in mind it starts and then shuts off until the engine is running. I got nervous and thought I wired it wrong.

One thing to keep in mind is that the tach pulse out of the PCM is for a 4 cyl so if you set your tach for 6 cyl it will read low. I did that and was overrevving during break in.
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Unread 10-13-2015, 02:34 PM   #7
yohan1979
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In many of the write-ups, the authors refer to 'cavity numbers' in the PDC, which guides you to the wires in that cavity and then specifically the wires needed for that circuit. I've been referencing several sites and write-ups as I work through it, but I don't want to publish them here until I have a rock-solid understanding and running rig (so the next guy doesn't go through this mess too).

I'm using the 4.0 alternator and had no intention of deleting the PCM so I'm not sure what you mean by "need the PCM control". The 4.2 alternator required an excite wire (brown) and I believe the stock 4.0 harness, PDC and PCM have that covered so I should be able to delete that brown wire from my loom.

That's the proper operation on the FP, primes then shuts down and then back on once running and it sounds like you went with the stock circuit which is what I believe I should do as well.

Good heads-up on the tach signal; I'll keep that in mind.
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Unread 10-13-2015, 03:09 PM   #8
RenoF250
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Quote:
Originally Posted by yohan1979 View Post
In many of the write-ups, the authors refer to 'cavity numbers' in the PDC, which guides you to the wires in that cavity and then specifically the wires needed for that circuit. I've been referencing several sites and write-ups as I work through it, but I don't want to publish them here until I have a rock-solid understanding and running rig (so the next guy doesn't go through this mess too).

I'm using the 4.0 alternator and had no intention of deleting the PCM so I'm not sure what you mean by "need the PCM control". The 4.2 alternator required an excite wire (brown) and I believe the stock 4.0 harness, PDC and PCM have that covered so I should be able to delete that brown wire from my loom.

That's the proper operation on the FP, primes then shuts down and then back on once running and it sounds like you went with the stock circuit which is what I believe I should do as well.

Good heads-up on the tach signal; I'll keep that in mind.
Yeah you can ditch the 4.2 alt wire. Having the 90A alt is much better.
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Unread 10-15-2015, 04:35 PM   #9
83threeper
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Im making this swap as well and ive basically made the decision to go with the hesco harness to try and save some headache. I haven't been able to find any detailed right ups on using the factory xj harness.
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Unread 10-15-2015, 05:17 PM   #10
RenoF250
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Originally Posted by 83threeper View Post
Im making this swap as well and ive basically made the decision to go with the hesco harness to try and save some headache. I haven't been able to find any detailed right ups on using the factory xj harness.
It is really not that big of a deal, just label the connectors as you take them off and remove the ones you do not need. I think I spent about 3 hours on it being very anal.
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Unread 10-15-2015, 05:29 PM   #11
Mp5ben
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I just found a 4.0/trans combo near me with 86k from a 92 XJ for $400 so I'm now seriously considering the swap. What are you doing about your gauges? I'd like to keep the CJ gauges. I think the oil pressure and temp is straightforward but what about the Tach, speedo and fuel? The XJ harness just runs with the original CJ harness correct? the 5 wires for ignition and running?
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Unread 10-15-2015, 06:41 PM   #12
83threeper
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Originally Posted by RenoF250 View Post
It is really not that big of a deal, just label the connectors as you take them off and remove the ones you do not need. I think I spent about 3 hours on it being very anal.
Cool, ill be referring back as i go. I just got my 4.0 cleaned up so next is getting it in. What holes do you use on the engine block for the engine mounts if you don't mind me asking.
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Unread 10-15-2015, 07:25 PM   #13
RenoF250
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Quote:
Originally Posted by Mp5ben View Post
I just found a 4.0/trans combo near me with 86k from a 92 XJ for $400 so I'm now seriously considering the swap. What are you doing about your gauges? I'd like to keep the CJ gauges. I think the oil pressure and temp is straightforward but what about the Tach, speedo and fuel? The XJ harness just runs with the original CJ harness correct? the 5 wires for ignition and running?
Tach is the only issue, you would have to get a 4/6/8 selectable aftermarket tach or use a 4 cylinder tach. The 4.0 PCM puts out 4 cyl pulse.

Fuel, temp, speedo, and oil pressure don't touch the PCM and work fine on their own.

No the 4.0 needs its own harness for the injectors, PCM, TPS, etc. I ripped a lot of the main CJ harness out. You just connect the main ignition leads to the 4.0 harness.
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Unread 10-15-2015, 07:28 PM   #14
RenoF250
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Originally Posted by 83threeper View Post
Cool, ill be referring back as i go. I just got my 4.0 cleaned up so next is getting it in. What holes do you use on the engine block for the engine mounts if you don't mind me asking.
Stock engine mounts from 4.0, there are 3 holes on each side of the block for them. One of the holes on the drivers sides is metric but a 7/16 will screw in all the way, just loose.

There are extra holes in the frame for the mounts and I believe I used the front holes.
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Unread 10-15-2015, 09:12 PM   #15
jason280
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I'm in the middle of doing a similar swap, using a '95 Cherokee in an '85 CJ. Only real difference is I am going with an AX15, so I will need an adapter for the Dana 300. I went ahead and tore my donor engine down, even though I was told it ran, as it was simply a lot easier to do before I bolted it in the CJ. I had it cleaned up, vatted, head rebuilt, and have a rebuild kit waiting....block has been bolted to an engine stand for months, just have taken the time to get it reassembled!
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