electrical differences in the 87 model if any?

I'm looking around for another XJ/MJ, yes just like a lot of us seem to be doing.
I like the mechanics of the vehicle and the straight forward design, I also like the RENIX system and want to get another rig that has it on board, but a question arose I cant find a direct answer to.
I read [http://www.naxja.org/forum/showthread.php?t=50209&highlight=year+differences] this[/url] about all the mechanical bits and pieces. The only thing not uncovered is how compatible the electronics are between the models. There's a lot of talk starting at 88 and up, and it seem people drop the 87 from that list even if it has the same body and engine.
In this thread post #15 brings up this topic that is not answered and I wonder if it's part of the electronics that make this difference.

the_bandit87 said:

Just on the topic of RENIX engines, why are 87 4.0s listed as 173hp and all other newer RENIX 4.0s (88-90) listed as making 177. Did they change something to add 4 hp, or did they just re-test the engine? I've been trying to find out for years why mine is only rated at 173. Also torque for 87s is listed as 220 and 88 and up is 224.

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The few books (and their not FSM's) I have about the Cherokee don't make it any plainer for me. The computer seems to be the same but some of the body wiring is different, like power doors (from my books 87 didn't have them) and minor things like that.
I know some of you have fleets of these nice machines can someone just weight in here and confirm or deny electrical differences in the ECU control if any?

Electrically, the 87 and 88 are nearly identical (I've got both.)

There are some differences between the 88 and 89, but those are mainly wiring colours, with some small sensor differences thrown in (I think the crankshaft position sensors are different on either side of the cusp, as I recall - but they'll still swap! I've got two 89's as well...)

Manufacturer horsepower/torque claims have been rather specious for a while, and I take most of them with a grain of salt. There was a blurb a few months ago on how the testing was going to be revised for a more "real-world" approach, and how the numbers are usually "optomistic" (read: overstated) in order to sell vehicles - just like the MPG figures have been generated on a treadmill for the longest, rather than actually running the thing (those numbers tend to be "optomistic" as well.)

Apart from that, the 87-90 are almost fully compatible that I know of, and there's no reason at all to discount the 1987 from your choices. There were some mechanical changes mid-year 1989, but those were due to ChryCo taking over production, and mainly have to do with things like deleting (finally!) that damn Peugeot gearbox for the AX15.

5-90

I had an 87, and it was definitely a good vehicle. Most of the changes between that and 89 are minor. One major one is a redesign of the engine bay wiring harness to eliminate a problematic connnector, but this affects only the harness itself, not the sensors or the computer. And 87's and 88's with the connector will still work fine if you keep it clean.

The ECMs were updated a few times after a few problems. There are four model numbers (for the manual transmission XJs) that are all interchangeable; however, the higher numbered ECM is preferred.

ECMs for Automatics and Manual transmissioned vehicles are different and are not interchangeable.

I just thought I'd chime in here. I found out later on (I've never sceen proof but...) that the 88s got fuel injectors that flowed a little better (i forget the exact measurement). That would explain the small output difference. I've scraped a 1990 Jeep and just about everything is identical. For the first few years chryco just carried over, stamped (CHRYCO) on a few things and dropped the french tranny, and addopted the 8 slat grill instead of the one I have (I think I have 11 slats in mine). Oh and they changed some of the colors around along the way. And the iluminated vanity mirrors from a 90 won't fit an 87 (just for future reference, differnet wires and mounts) one thing that I find extremly cool about the 87s is that their power windowes motors are made by Rockwell International. How many ppl can say that their windowes motors are made by the same company that made the B-1?

AJPulley said:

The ECMs were updated a few times after a few problems. There are four model numbers (for the manual transmission XJs) that are all interchangeable; however, the higher numbered ECM is preferred.

ECMs for Automatics and Manual transmissioned vehicles are different and are not interchangeable.

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HUH? You mean the computer is different between auto and manual trannies? I thought it was the same and the TCU( tranny control unit) was separate on the auto for the 87-90 years?

onetallmj said:

HUH? You mean the computer is different between auto and manual trannies? I thought it was the same and the TCU( tranny control unit) was separate on the auto for the 87-90 years?

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Nope. All the RENIX ECMs have a part number of 895300XXXX. The last four digits usually end in an odd number for manuals and even for autos, though I do believe there is an odd-ball or two out there.

Yes, the automatic transmissions also have a TCU in addition to the ECU. The TPS is differant for the autos as well, but will work in a manual transmissioned XJ. It will not work visa-versa.

I like my 87 just fine. The c-101 connector on the firewall is a known problem, and taking it apart is a PITA to service it, especially with a clutch master in the way.
That's something to check if it's an older XJ/MJ with a manual trans. Make sure that the fuse block and the connector tat goes through the firewall to it are in good shape. The Master Cylinder tends to leak, and wen it does it drips right down onto the fuse block. Brake fluid turns that plastic into a mush after time, and will destroy every fuse in there. If it leaks it must be taken care ASAP to avoid permanent deformation, then fuses don't sit right and so on and so forth.

The main difference I've noticed is the addition of the ballast resistor for the fuel pump in 88. The fuel pump wiring circuit is a little different. Also the starter relay is different, which is also part of the later fuel pump circuit. Some of the harness is routed a little differently from later models.
There are other harness differences, most are minor. In export models they get a little more envolved.
One thing I've seen pop up over and over again is the differences in the harness for the same year and model run. You'd think the harness for the same year would be nearly identical, the differences aren't major but they are there. I've often thought that one reason could be that they ran out of the proper harness for a particular package and substituted another that would work, but usually with a few extra go noplace connectors and wires. You sometimes get little unexpect goodies, like the fog light relay installed, but no switch, just a connector hanging, things like that. I have the heavy duty turn/brake/light relay trailer package (harness) in my 88 (that was never ordered).
If you look at the XJ harness and reverse engineer it a little, you can see that much of the harness is add ons. Instead of redesigning the complete harness they added another wire, instead of integrating the new circuit.
If you work with the harness and electrical some, you can also see where different design teams added different pieces (over the years), it lacks continuity in design in some places. I've often thought this is one reason the electrical system often seems a little buggy.
One good tip I can give you, I did it on my 87, my 88 and my 96, is too follow most every wire you can and deal with the rub spots before they turn into rub throughs and shorts. A handfull of cable ties and a selection of slitted plastic cable coverings (from the local junk yard) can save you a lot of grief, especially if you plan on doing a fair amount of dirt roading and bouncing things around a lot.
Under the dash, the harness rubs in many places. Also under the hood and chassis. Be carefull and thoughtfull, when pulling and tieing and rerouting cables, it's a bumber to cause a faulty/loose connection that you have to chase down later.
The power steering hard line (or the tranny cooler line) often rubs on the top of the steering box and will eventually rub through. Most all of the rubber tubing (everywhere) needs to be checked for rubs. Electrical isn't the only thing to check for rubs. Most everytime I'm under the XJ or have the air box out or something else disassembled, I notice something that needs to be protected, tied down or rerouted a little. Behind the tail lights and the healdights, the wiring is kind of a mess and there are other trouble spots.

something else I thought of that 8mud reminded me of under the hood.
The vacuum harness under the hood. Go over that carefully, the nylon tends to crack. Mine had 3 cracked lines, one at the "tree" and two others in the lines themselves.
You're also want to make sure that the closed cooling circuit bottle is in good shape before you go on any long trips. t's not something that you can buy anywhere on short notice, and it's a deal breaker if it pops a long way from home.