Switching From Renix to OBD11 ~ Considering ~

[Drahcir495]

The Jeep mechanic I have my Comanche at would like to switch from the Renix engine management system to the newer versions that are used for the later HO systems (OBD1?). I have a 4.0 out of a 98 XJ running on the Renix system now. I can't remember all that was involved in getting it all to work, but it's a hybrid of the two. He tells me that the newer management systems are far superior and are much more abundant than the, what is becoming harder to maintain and find, Renix system. What do you think the pros and cons of this be? I was worried about possible confusion in parts and maintenance if I should need to have anyone else work on it. But then again, as I said above, it's now a confusing set up to explain any way. I may have just answered my own question, but it would be nice to hear it's the better plan.

[eaglescout526]

Sounds like he doesn’t know how to work on the ancient stuff. Renix is pretty easy to work with. Cruiser I’m sure would have some witty rebuttal telling you to take it elsewhere or do it yourself. A lot of diagnosis is honestly with a multimeter in which your measuring voltage across the sensors and making sure they’re getting the right 5v and outputting what they should be according to which ever shop manual from AMC. 
 

Sure Renix doesn’t offer more power but it’s got some unique advantages that the HO doesn’t have like compensation of using higher octane and being able to work with a stroker. But diagnosing Renix is really easy. 

[ghetdjc320]

96+ was OBD2. OBD1 was only in use for 91-95 on the XJ platform. Obd2 does indeed have more potential as the maps can be edited easily enough. However, unless you plan on modifying your engine significantly, there isn’t anything to be gained by just swapping the obd2 system over on a stock setup. An REM scanner will provide a host of diagnostic data as well for Renix. 
 

[Drahcir495]

3 hours ago, ghetdjc320 said:

96+ was OBD2. OBD1 was only in use for 91-95 on the XJ platform. Obd2 does indeed have more potential as the maps can be edited easily enough. However, unless you plan on modifying your engine significantly, there isn’t anything to be gained by just swapping the obd2 system over on a stock setup. An REM scanner will provide a host of diagnostic data as well for Renix. 
 

I replaced the original 89 motor for the 98 4.0 out of an XJ, so I don't know if that would simplify the process? 

[Drahcir495]

5 hours ago, eaglescout526 said:

Sounds like he doesn’t know how to work on the ancient stuff. Renix is pretty easy to work with. Cruiser I’m sure would have some witty rebuttal telling you to take it elsewhere or do it yourself. A lot of diagnosis is honestly with a multimeter in which your measuring voltage across the sensors and making sure they’re getting the right 5v and outputting what they should be according to which ever shop manual from AMC. 
 

Sure Renix doesn’t offer more power but it’s got some unique advantages that the HO doesn’t have like compensation of using higher octane and being able to work with a stroker. But diagnosing Renix is really easy. 

It would have been great to hear from Cruiser on this. And of course, Don. He says he will no longer be working on the Renix systems after mine. I won't be running a stoker because of the horror stories about getting them to run correctly and I'm now to practical with my aspirations - keeping it simple lol.

[eaglescout526]

12 minutes ago, Drahcir495 said:

It would have been great to hear from Cruiser on this. And of course, Don. He says he will no longer be working on the Renix systems after mine. I won't be running a stoker because of the horror stories about getting them to run correctly and I'm now to practical with my aspirations - keeping it simple lol.

Lol fair fair on the stroker. 

 

But I think all I can say is just how purely simple Renix is to work on and diagnose with just only a mulitmeter. Most dont like it cause its old and ignore how simple it really is. Sure not alot of info out there anymore but theres a trove of us on here and cruisers tips to help. 

[Drahcir495]

17 minutes ago, eaglescout526 said:

Lol fair fair on the stroker. 

 

But I think all I can say is just how purely simple Renix is to work on and diagnose with just only a mulitmeter. Most don't like it cause its old and ignore how simple it really is. Sure not alot of info out there anymore but theres a trove of us on here and cruisers tips to help. 

There sure is a lot of support on here indeed. I just wonder if I have already pushed passed it with the 98 I put in it? The whole engine - motor, exhaust, injectors, TB etc. The only thing is the fuel rail and Renix management system on it. I would Have to only figure out how to make the HO fuel rail work on the new motor?? I think i jerry rigged the stock one on it, but it's been so long I don't Rember?? I do already have Nicks REM here in a box I could use for diagnostics. Now, I'm leaning back towards the Renix 

[eaglescout526]

I think the only con is just parts. Renix parts are getting harder but we are finding modern alternatives to the parts we cant find. I have found several aftermarket stuff thats not really labeled for Jeep but look the same and are labeled for Renault which shared alot of components.

[Drahcir495]

That is promising. I been picking up any Renix computers I can find. They are going for 90 bucks here but it is very nice to have spares. The switch would also require the complete wiring harness and possibly the gauge cluster. It is a lot of work that would be involved and $. I really need to research how others have adapted the fuel rails. I would also like to replace the home made ( I'm so tired I can't remember what the part is called that opens the TB plate) with the one that Hesco sells.

[89 MJ]

Sounds like you’ve got yourself talked into keeping Renix, which I think is the right call. With Cruiser’s info, it shouldn’t be too hard keeping these rigs on the road. To be honest, OBD1 does not seem like an upgrade over Renix. I don’t think there are as many knowledgeable people in the ODB1 crowd. 
 

I could see doing an ODBII swap for easy diagnostics, but that’s a ton work and if your truck hasn’t had much for issues to this point, it seems like a good way to end up with issues. 

[pizzaman09]

On paper, the improvements in power that OBD1 provides over remix are more likely due to head and intake port design.  The OBD1 heads just flow better.  By 1989 the Renix engines only made 9 less horsepower than the HO OBD1 4.0L engines.  

[75sv1]

I started down this/that path. I really doubt its worth it. I am more looking at a 2000-2001 setup. Yet, that has its issues. Having those issues with a 2000 XJ. Starting to look at a FAST or other aftermarket solution. Also, bored TB should help the power. I thought my '88 MJ had more power than any of my '98's and '00 XJ. But manual vs Auto, and I might have had a 3.55 D35 rear with 225 tires. 

[Gojira94]

2 hours ago, pizzaman09 said:

On paper, the improvements in power that OBD1 provides over remix are more likely due to head and intake port design.  The OBD1 heads just flow better.  By 1989 the Renix engines only made 9 less horsepower than the HO OBD1 4.0L engines.  

 

I think this is the crux of it. The 91+ HO rearrangement of the head ports and slight improvement of the intake manifold itself explains the gain in volumetric efficiency, and accompanying bump in HP. I've looked for hard numbers on actual VE of the original Renix design, VE improvements in the 91-95 changes along with the 7120 head, and any further gains to VE with the 99-01 intake. The 0331/ 0331 TUPY head didn't really gain much if anything over the 7120. Best guess is the Renix design was capable of maybe mid-70s % VE, 91-98 HO maybe low 80s %, and 99-01 possibly mid-80s % VE.

 

To clarify, Volumetric Efficiency is a measurement of how efficiently a cylinder fills during the first stroke of the cycle. The immediate way to improve that without changing the head's intake and exhaust ports (think mild to moderate porting) is to free up induction and exhaust by whatever means is practical (reduce intake manifold and exhaust restrictions). Forced induction will get the most bang for the buck, and can take even a stock Renix engine into the mid-90s % VE. Renix can adapt and handle increased VE up to a point, the failure-prone 91-95 ECMs certainly not, and 96-01 with very limited support by very few tuners. The 96-01 have common ECM-based alternator voltage regulation failures, though they can be overcome with installation of an external Mopar voltage regulator and a diode for the ECM.

 

If a 99 XJ that had been crushed by a falling tree fell into my lap for $500, and my MJ had come to me as a rolling shell, I'd certainly swap everything; drivetrain, interior, every bit of electrical harness I could use, ECM, airbags, tea, cake, the whole shebang. Instead, I'm using the 89-90 Renix setup someone tossed in before I got it with a complete drivetrain from a 93 YJ. Even the 01 XJ still has the crank position sensor... Coil near plug is nice but still not enough incentive for me to spend the coin to convert from Renix. BSE still rebuilds the Renix auto and manual ECUs and they cost (at this time) a little over $100.00. Renix may be a little harder to wrap your head around at first but I see no added value for converting to OBD-I or OBD-II if a Renix system is present, complete and functioning.

[pizzaman09]

@Gojira94 I fully agree.  The reverse flow head of the 4.0L is never going to have amazing VE numbers but there were good improvements over the years to make it better.  

I do like the Renix system for how easy it is to understand and the vast knowledge that exists on it.  When searching for a Comanche I was specifically looking for an 89 or 90 Renix 4.0L as I knew it was pretty well supported.  The early 90s OBD1 systems that are in many cars scare me as the support for those is often through early, hard to get a hold of code readers.  Renix is pre OBD1, stores no codes, and can be diagnosed with a multi meter.  On top of it, the REM takes all of the hard work out and tells you what each reading is.

[ghetdjc320]

I wouldn’t say the 91-95 ecu’s are unreliable. They are a fully potted ecu and they live under the hood. There are a few out there who have chipped and tuned them even for boost. There are also adapters for the obd2 ecu’s to obd1 harness. The alternator voltage regulator became an ecu function in 91+. 
 

As for diagnosis, many times it’s not as simple as just grabbing a multimeter to fix a Renix. Some of our recent repair posts have proven this. It can also be tough to find some quality Renix replacement sensors. 
 

Ultimately each system progressively evolved a bit in certain areas. But a modern stand alone ecu will be far ahead of all the factory system. Lots of Renix MJ’s out there still running strong though.

 

Id agree though that swapping to obd1 is not worth it.

[75sv1]

Gojira94

'The 96-01 have common ECM-based alternator voltage regulation failures, though they can be overcome with installation of an external Mopar voltage regulator and a diode for the ECM.'

Any info on this. Having issues with my 2000 XJ misfiring. I did have the ECM checked out. I think other issues at play. Light to the Air Bags is on. I've hear it shared the same power supply as the TBS. 

[75sv1]

5 hours ago, 75sv1 said:

Gojira94

'The 96-01 have common ECM-based alternator voltage regulation failures, though they can be overcome with installation of an external Mopar voltage regulator and a diode for the ECM.'

Any info on this. Having issues with my 2000 XJ misfiring. I did have the ECM checked out. I think other issues at play. Light to the Air Bags is on. I've hear it shared the same power supply as the TBS. 

OK, found some info on the Net. Not sure if it is my issue or not. Still, worth a try. 

Also, there was a Cam change in the 96-01 or even up. As to lift. A bit less than the HOs, and Renix. But a split lift as a bit more lift on the exhuast. the 99+ also has a thrust plate to locate the camshaft. In the past few years, there are performance cams for the 99+.

[Gojira94]

Yeah, I had a couple gaps in there, you're correct about the cam changes, and ghetdjc320 pointed out that 91-95 also had the voltage regulation controlled by the ECU. 

https://alternatorparts.com/external-voltage-regulator-high-output-alternator-kit.html  >> ERCKFRM (for ECU side regulation failures, without replacing the ECU)

(FRM goes to the 2 alternator wires that would otherwise be connected to the ECU)

[Drahcir495]

Thanks for all the great advice! I'm staying with the Renix. I also already have Nick's REM

so that's one more reason to keep it simple 

 

[Drahcir495]

The decision has been made for me. It is the OBDII out of a 96 XJ going into the truck. The harness and computer have already been purchased and the Renix harness removed. I had agreed to the swap before having second thoughts. Understandably my fault. I’m feel a little better knowing it’s the OBDII though.

[89 MJ]

Except 96 is completely on its own for most of the wiring, from my understanding. I know the ECUs are on there own, and seem fairly prone to have issues where they won’t rev over 3,000 rpm 

[eaglescout526]

18 minutes ago, Drahcir495 said:

The decision has been made for me. It is the OBDII out of a 96 XJ going into the truck. The harness and computer have already been purchased and the Renix harness removed. I had agreed to the swap before having second thoughts. Understandably my fault. I’m feel a little better knowing it’s the OBDII though.

That’s hell of a 180. Haha. 

[Gojira94]

1 hour ago, 89 MJ said:

Except 96 is completely on its own for most of the wiring, from my understanding. I know the ECUs are on there own, and seem fairly prone to have issues where they won’t rev over 3,000 rpm 

 

And IIRC, the 96 MAP sensor is a one year only thing. Mounted on the throttle body, has same output as 87-95, just packaged differently, looks like the 97-01?

[Drahcir495]

5 hours ago, 89 MJ said:

Except 96 is completely on its own for most of the wiring, from my understanding. I know the ECUs are on there own, and seem fairly prone to have issues where they won’t rev over 3,000 rpm 

Great . I expect him to get that all figured out. I just want it done at this point. I think it was dropped off last April. 

[Drahcir495]

5 hours ago, eaglescout526 said:

That’s hell of a 180. Haha. 

I know . I was convinced to just go Renix. I think he said 96.