easiest 4.0 to work on

[hankthespacecowboy]

The 4.0 in my '90 XJ is near the end of it's life after 273,000 miles. My biggest consideration in looking for a new (used) donor motor is ease of wrenching. I've found the Renix MPFI to quite frustrating to work on, given the immense amount of variable between vacuum lines and wiring clusters. I have read that the '91 and up Chrysler 4.0 HO motors have a simpler f.i. system. Is this true or no in anyone's experince?

Thanks,
Hank.

[90xj06]

comming from a 1986 nissan 300zx in the winter. the 90 jeep is soo easy to work on. even changing the fuel injectors where easy

[old_man]

If working on the Renix is a hassle for you, don't even think about the effort required to convert to the new computer system. The rewiring is is a royal pain and I'm a EE. Also in Colorado, if you live in a smog check area, you have to go to a state owned regional station, not your local tail pipe sniffer, and there you have it gone over with a fine tooth comb. If they are satisfied they will give you a waiver letter.

[5-90]

Physically, they're all much the same (1987-2007.) Technically, there are differences - and I'm assuming that's what you're referring to.

If you go OBD-I (1991-1996) or OBD-II (1997-2007,) you'll be wanting some sort of "code reader," and you may have issues with getting a MIL wired up into the dash panel. OBD-I will probably be easier for you, since you'll be able to fit up an OBD-I gage cluster (1991-1995/6, before the ChryCo redesign.) OBD-II drives all of the gages off of the CAN bus, which is already going to be a huge wiring job (moreso fitting the gage cluster, I fear...)

If you're going to do a swap of that magnitude, I'd suggest getting a compleat donor vehicle (rollover?) - not only to make sure you get everything, but so you can see where it all was before you get it out and move it over!

Still, I've found RENIX easier to work on than OBD-I/II - probably because I came up on points and condensers, and I'm used to doing my own troubleshooting. There's a good deal of RENIX technical know-how on this board, it's not a bad system, and most of the engine management sensors are General Motors parts - which makes them easier to find.

All else being equal, I'm probably going to tell you that it's easier to just learn the RENIX system (it's a fairly quick learning curve, once you get started. I can probably provide you with some tech material if you'd like,) than to undertake swapping to OBD-I/II. However, if your heart is set upon "upgrading," might I ask that you keep all the RENIX control electronics, include a note with detailed application information, and contact me for my address later? I'm working on reverse-engineering the RENIX system for a number of other projects, and donor electronics make me fear blowing something important rather less...

5-90

[90xj06]

what type of computer does the 90 have as to odb1/2 or is it that weird one.

[5-90]

RENIX. ChryCo put their OBD-I in for the 1991MY, then went to OBD-II for 1997. RENIX was used until the end of the 1990MY, as I recall.

5-90

[xjtrailrider]

I've got 4 XJ's, 90', 95', 96', 00'. I'm new to the RENIX system(I just got the 90') but I already like it better than the later systems.

[5-90]

I've got 4 XJ's, 90', 95', 96', 00'. I'm new to the RENIX system(I just got the 90') but I already like it better than the later systems.

Hey - I've got five rigs, and they're ALL RENIX! (1987, 1988, 1989, 1989, 1989...)

My attitude toward RENIX vice ChryCo OBD shows in someone's sig line - they borrowed a quote from me. I'm not a huge fan of OBD, and finding out it was started, essentially, by CalEPA doesn't do it any favours in my mind (and I started doing mechanical work on Corvettes from the 1960's and 1970's - my uncle's collection.)

I'm just too used to doing my own troubleshooting (on pretty much everything, in fact,) to want something that is supposed to diagnose itself and make it easier for Zimbu the Monkey to work on it. Mechanics that can diagnose are becoming a dying breed, I think...

5-90

[90xj06]

so how do you diagnose a renix computer

[Matthew Currie]

RENIX. ChryCo put their OBD-I in for the 1991MY, then went to OBD-II for 1997. RENIX was used until the end of the 1990MY, as I recall.

5-90

minor correction: 96 is OBDII, but still gives OBDI codes too.

[5-90]

minor correction: 96 is OBDII, but still gives OBDI codes too.

Ah - half marks for me, then. I sometimes get that transition year wrong - probably because I just don't care about OBD...

Thanks!

5-90

[hankthespacecowboy]

thanks for the all the info. Guess I'll be staying with Renix and ramping up my learning curve. You'll probably be hearing more from in the future...

[langer1]

easiest 4.0 to work on
Some one else's with lots of money

[5-90]

thanks for the all the info. Guess I'll be staying with Renix and ramping up my learning curve. You'll probably be hearing more from in the future...

No ache. We'll be here...

5-90

[87manche]

so how do you diagnose a renix computer
A multimeter and a factory manual mixed in with some common sense.