Renix ECU experts/pros

Wasn't sure which board to post this one (so i chose the OEM board).

Here's the situation. I have an 89 XJ that *used* to have an automatic transmission. As it has been documented over time ... i have since swapped in a AX-15 trans.

At the time, I simply removed the TCU and made some corrections/terminations in the wiring harness.

Fast forward 6+ years and my computer has finally passed on. I'm trying to determine if i want another ECU for an auto trans. Or would i want to purchase one for a manual trans.

I have contacted the rebuilder (A-1 Cardone) regarding the plug/pin configuration. They are identical. I have been able to determine that the manual ECU has a slightly faster timing advance. Past that, I'm unable to determine any additional differences between the computers in terms of capability or compatibility.

The biggest difference, i've found so far, is the price. The manual ECU is 87. The auto ECU is 101. Most folks locally (and the tech at Cardone) suggested to just get another auto ECU .. since it has worked for 6+ years without any codes.

Can someone offer insight regarding with ECU to get ... or direct me to something that can offer concrete info on the differences between the two?

I will be cross posting this to a few other boards as i'd like to have some clue as to what to do by the end of the night. I will be ordering the ECU in the morning (to get it for the afternoon).

Thanks much folks !

Joe Attardo

Unless you've run a dealer's scan tool on the XJ you won't get any codes, because the Renix ECU doesn't flash codes or light up a Check Engine light.

Frank Swygert on the Yahoo Strokers' group has been running a stroked 4.0L in a '63 Rambler wagon for several years. I sort of recall that he's using the wrong ECU and hasn't had any problems.

If I were in your situation, I'd get whichever is cheaper. The fact that the cheaper one happens to be "right" for your tranny is just a bonus.

Eagle,

Thanks for the quick response.

I was well aware of the code situation/check engine light. I should have mentioned that i had it scanned (for free, i might add) with the Snap-On code scanner and correct Renix plug. I apologize if i was vague on that matter. All readings/voltages came up as they should have each time i had it scanned over the years.

I'm still bouncing around in confusion. I remember Frank's rambler motor buildup ... but forgot he existed until just now. Part of me isn't sure if the manual ecu has some differences now that i've changed the harness a bit. But the other part tells me it wouldn't matter.

I'm going to wait and see what the peanut gallery has to offer and answer any questions you may have to offer a more educated response. :anon:

Thanks much !

Joe

As I recall, the principal electrical difference between Manual and Automatic Renix XJ's is the presence or absence of the TCU for the AW4 - omitted, of course, for the Peugeot or other row-yer-own.

I can see why there would be a slight difference in cost - probably due to the programming. I'd be worried if the difference were more than it is, but a difference of $14 is not outlandish nor is it entirely unexpected.

Also as I recall, there was only one listing for ECU pin breakout in the Renix FSM's - so there's no change to worry about externally. When the ChryCo electronics picked up, they went to their PCM setup (Powertrain Control Module) rather than the seperate ECU/TCU us Renix guys are used to.

I will, as is pattern, agree with Eagle on the "get the cheaper" philosophy - the fact that it is direct replacement for OEM is an added bonus. Since you're still looking at less than a Franklin, you're doing pretty good...

BTW - how, precisely, did you kill off your ECM? I have three Renix XJ's (87/88/89) that still have original electronics, save the ignition module in the 88 (and I haven't figured out just how I killed THAT one yet!) I have to admit, I am most impressed with the service longevity of Renix electronics...

5-90

I'm guessing it was just age. 14 years.

The fuel pump relay is no longer receiving ground from the computer. All other tests have been done/checked.

it's a start but no run condition. When i bypass the relay ... direct juice to the ballast resistor .. the pump runs and stays running.

When i start normally .. it runs for 2-3 seconds then dies. Keep squirting ether .. it stays running.

I've check the coil/module. Testing all leads for juice or ground depending on which wires i was looking at. If i ground the relay directly .. it runs normally. I've traced the wire back the entire way. All good. No chaffing or signs of problems. It's possible the wire could be broke internally ... but i'm not about to do that. Less work (tho more money) to just replace ECU. 3 bolts & 1 plug.

If you have any other ideas or questions about what i've tested .. post them here or privately ([email protected]) and I'll go into greater detail.

At this point .. i know it's not the fuel pump because when you jumper the relay ... it runs. All the relays are less than 1 year old. And i swapped them around with no difference. I got (and was able to return) a new module to eliminate that possibility. All sensors have no more than 7K on them (when i rebuilt the Jeep). The starter relay was also changed 7K ago (and i swapped/returned a new one JUST to make sure). Gotta love working P/T at the auto store.

Can't think of anything else off the top of my head. Ask and I'll try to give an answer. Been at this for 2 weeks now on/off ... and i need it DONE.

Joe

Sounds as if you have done about everything, but I'm just wondering if you have tested all the wiring to the relay itself for continuity. It would be a pity to get a new ECU and find that the harness is bad.

Matt,

I used the circuit tester. All other wires to the relay work/have proper juice EXCEPT the ground. And i already chased that back and didn't find anything.

I too was suspicious on the computer deal .. knowing the longevity/simplicity of the renix setup.

I'm still open to other ideas or different testing methods.

Joe

Joe, is the wire that we're talking about, the orange/black one going from the fuel pump relay to the ECM? This is indeed the ground for the FPR, but I think it's supposed to be grounded at all times, not just with the key on.

You can try running a jumper ground wire from the FPR (orange/black terminal), to a nearby screw that's grounded. Then see if the fuel pump works normally.

As Matthew says, this is probably a wiring glitch, and a new ECM might not fix it anyway......

R.O.E


No .. it's teh black with yellow tracer. And yes .. we jumpered it. I think i said that in the original post. When we jumpered .. the truck said running until I took the jumper off.

Well ... I ordered the ECU. It'll be here tomorrow. I'm doing the best i can. Will let you all know tomorrow evening if it works (maybe even the afternoon if i have time .. have to take care of my quarterly taxes).

Will keep you up to date.

Joe

Update

Well,

Changed the computer. Wasted 87 bucks. :bawl:

I checked the harness again going and coming out of the pump relay. Can't find a single thing. I'm at the end of the line and i'm bringing it up to a good dealer in my area (that i actually trust).

I've spent 3 weeks on/off trying to get it running 'normally' and i don't know what else to do at this point. If a local person wants to give it a whirl .. i'll pay for lunch/pizza/gas. I'm in NE PA.

Will be calling to see when the dealer can do it. I will either jumper the relay and drive up. Or hook up the tow bar and flat tow it.

:doh:

Joe

Joe --

I don't have an '89 FSM. The '88 wiring book shows the fuel pump relay ground as orange w/ trace, and it does run directly to the ECU. However, the book doesn't show what goes on inside the ECU so I don't know where it goes from there. The wiring diagram doesn't show any terminal labeled GROUND for the ECU, so it must ground through the case (?).

I don't see anything that looks like a black wire w/ yellow trace. Either '89 is different from '88, or you're tracing the wrong wire.

Eagle,

I'll look thru my FSM tomorrow. It's late and i'm cranky.

Look for a thorough response tomorrow on teh colors/tracers and what my FSM calls each wire.

Thanks !

BTW ... i'm only 2 hours from ya

Joe

The ECU ground is in the same place as batt ground on the engine. The battery cable goes to that stud as does a couple wires which lead back to the ECU.

Perhaps check those wires for wear or remove and clean those connections?

Joe Attardo said:

BTW ... i'm only 2 hours from ya

Joe

Click to expand...

Not the way I drive. Port Jervis/Milford is 2 hours. Paragon is 4 hours.

Of interest to you - I'm upping 88 FSM electrical info to my briefcase, and you should be able to access it if you have a copy of Acrobat. You'll find it in the "Automotive" folder, public access.

5-90's Online Archive

5-90

5-90

Thanks for the offer. I have my 89 FSM in teh garage with me. So unless i'm reading the manual wrong .. i'm pretty certain i have the right wires.

I'll be fiddling with it tonite and will get back to you guys on teh wires/colors/what i did (again)

Joe