what numbers have to match on a replacement computer? - Page 2

5-90 · 06-19-2012, 02:17 AM

Quote:

Originally Posted by ratmonkey

I agree with 5-90. Never thought I'd write that.

Fuel maps, timing, and idle characteristics are very different between manual and auto pcms/ecu's.
First hand experience speaking here as well.
Salvage computers are hit or miss, dodge/Chrysler/Jeep computers have a nasty habit of going bad when it sits on a shelf or isn't used for randomly long periods with no battery input. No one seems to have an answer to that issue.

I think it's due to cap failure - since a common repair/upgrade is replacement of caps inside the unit - particularly the KAM caps for the ECU - and I know that caps are like rechargeable batteries in that they'll want to be shipped charged.

I've run across that fault in a few GM units that I had to deal with - component-level troubleshooting is a pain in the arse, but doable.

**Que89YJ** · 06-19-2012, 05:36 AM

The reason we have a 33 code at all is because the cal is the same. Flashable calibration came in with the OBD II as did different calibrations for the different vehicles they flashed coming down Huntsville in the plant. The only real difference in any of the controllers was as I stated in the automatics with the nuetral saftety switch which you can bypass by grounding. As far as the EMI, yes that was the concern. It has been a few years now and the memory isn't as clear as it use to be but I can say with some real assurance that there isn't anyone that is more familar with that ECU. The standard set of tests required functional testing through dips, drops, ramps, spikes, load dumps, and radio freq. immunity in both common and differential mode. You can use any 91-95 ECU in any other on the XJ and YJ. They are totally interchangable. If you are looking for an ecu I can help you out there too. Call Chris at:

Call text email 810-650-3206 We buy sell and trade parts or full jeeps Visit our website: www.Cfoffroad.com
We have the knowledge and inventory to get you what you need.

He is a real good guy. If he can't help you out post back and there are a couple other places I can recommend.

**ratmonkey** · 06-19-2012, 07:31 AM

Quote:

Originally Posted by 5-90

I think it's due to cap failure - since a common repair/upgrade is replacement of caps inside the unit - particularly the KAM caps for the ECU - and I know that caps are like rechargeable batteries in that they'll want to be shipped charged.

I've run across that fault in a few GM units that I had to deal with - component-level troubleshooting is a pain in the arse, but doable.

maybe on the obdi, they're easy to fix so i wouldn't think that's the major mystery there. it's a total different story for the obdii units though. no one seems to have an answer to that, even the reman shops.

**jsawduste** · 06-19-2012, 07:52 AM

Quote:

Originally Posted by Que89YJ

The reason we have a 33 code at all is because the cal is the same. Flashable calibration came in with the OBD II as did different calibrations for the different vehicles they flashed coming down Huntsville in the plant. The only real difference in any of the controllers was as I stated in the automatics with the nuetral saftety switch which you can bypass by grounding. As far as the EMI, yes that was the concern. It has been a few years now and the memory isn't as clear as it use to be but I can say with some real assurance that there isn't anyone that is more familar with that ECU. The standard set of tests required functional testing through dips, drops, ramps, spikes, load dumps, and radio freq. immunity in both common and differential mode. You can use any 91-95 ECU in any other on the XJ and YJ. They are totally interchangable. If you are looking for an ecu I can help you out there too. Call Chris at:

Call text email 810-650-3206 We buy sell and trade parts or full jeeps Visit our website: www.Cfoffroad.com
We have the knowledge and inventory to get you what you need.

He is a real good guy. If he can't help you out post back and there are a couple other places I can recommend.

What Q says is truth. I have even talked to some of the original cal guys that were responsible for developing the programming for the OBD1 ECM`s. They were able to pull the old cal. tables up and verify the parameters.

Bets are off when you start talking OBD2.

And x 2 on the CFoffroad folks,

misfit650 · 06-19-2012, 09:11 PM

So will the computer out of a 94 yj 4 cylinder manual, Work in my 95 yj 6 cylinder auto???

**Que89YJ** · 06-19-2012, 09:21 PM

No, it has to come from the same engine.

**Que89YJ** · 06-19-2012, 09:22 PM

The trans does not mater. You just wouldn't have the Nuetral saftey switch with the manual ECU.

misfit650 · 06-19-2012, 09:57 PM

I dont know what any of this means haha, so no, it wont work?

misfit650 · 06-19-2012, 10:17 PM

Quote:

Originally Posted by Que89YJ

No, it has to come from the same engine.

So manual or auto dont matter, just has to be 6 cylinder for 6 cylinder?

What happens with no neutral safety switch?

Why do some say numbers hv to match etc etc?

**Que89YJ** · 06-20-2012, 04:33 AM

It will be able to start in gear. The engine size needs to be the same. I don't know why anyone else would tell you different. 91-95 ecu from an xj or yj with the same size engine.

**jsawduste** · 06-20-2012, 04:42 AM

Quote:

Originally Posted by Que89YJ

It will be able to start in gear. The engine size needs to be the same. I don't know why anyone else would tell you different. 91-95 ecu from an xj or yj with the same size engine.

Q is right again but I would like to add one fact.

If you use the XJ ECM make sure the donor vehicle did not have the factory optional security systems.

FWIW I have run XJ ECM`s in my YJ and currently have two of them set aside as spares. In fact I prefer the XJ version as it has a larger heatsink under the vented cover.

**ratmonkey** · 06-20-2012, 05:03 AM

if it came from an auto you'll need to run a wire to the pin for the neutral safety switch and ground it. it will NOT start if that is not grounded.

**Que89YJ** · 06-20-2012, 07:26 AM

Thanks for the reminder. You realise you can fix your own ecu. The brainsurgery is an easy fix and cost less then $10 to do yourself. Look at this thread:

http://www.jeepforum.com/forum/f12/c...rs-ecu-492597/

misfit650 · 06-20-2012, 10:31 AM

Ok, mines auto, so i need an auto one, i contemplated surgery, but i want a spare in case when i solder it n i ruin it.... So where does the ecu ground? If i rreplace with a matching one, where is the ground when i install it? And it WONT start if its not grounded?

**Que89YJ** · 06-20-2012, 10:51 AM

I went through this. You can get either one it doesn't matter. The fact that you have an auto means you do not need to worry about adding a ground for the NSS. If you get a manual ECU from a 4.0L XJ or YJ. You are making it way too complicated for yourself. Get an ECU from any 91-95 XJ or YJ. If the ECU came from a manual trans the Jeep will be able to start in any gear. That is the only difference. Period. Call Chris in the thread I posted and he will be able to help you find one cheap.