96 PCM swap??

[mindless]

Hey guys well in my quest to get rid of my CEL for code P0443 - Evaporative Emission Control System Purge Control Valve Circuit. Found no power getting to the solenoid and no power coming from the PCM. So looks like the PCM might have pooped the bed. Now my big question is what PCM can i use. Do i need a 96 cherokee only or is there other years or makes i can use. Not sure how easy it will be to find a 96 PCM locally. Any help would be great thanks in advance :cheers:

 

[Rags]

I am trin to remember if the purge solinoid gets it 12 volt power feed directly from the PCM..... if it does, I think you can add a fresh 12 volt fused keyed source wire to the solinoid to make it work...... the PCM turns the ground on and off, been awhile and I dont have an FSM in front of me....... if the 12 volt positive driver is out in the PCM this might fix it untill you locate a PCM.......

 

[mindless]

Cool thanks ill have to look into it a little better today I was looking for power and ASSumed that's what it needed

 

[mindless]

Ok well still no luck if I power the solenoid it seems to power other relays for what ever reason only time the solenoid clicks is with a fresh power and ground so on to my next question.

Does the number on the computer matter I was just looking on eBay and noticed some actually say 296 where others say different mine is the 296 not sure if it matters or not but should I just get the matching computer to play it safe?

 

[Rags]

How much are you willing to spend? I have used http://www.autocomputerexchange.com/

Tell them you saw them on EBAY as they sell there also and Ebay prices are lower then general sales..... I have used them on a good 10 PCM replacements for Dodge and Jeep last few years and held up well, prices are $159.95 to $179.95 with free shipping.... all depends on what PCM you have.......

Used and junk yard PCMS are a roll of the dice...... as for part numbers, as long as same year and configuration(IE federal/California, engine size, tranny, TLEV or not and so on) you should be okay using another part number.... again, roll of the dice......

 

[gradon]

I might have a 96 auto 4.0 pcm from one I parted out. . .

 

[Rags]

Also are you supplying new power 12 volts + to the correct side of the EVAP solenoid? after you wire it up you have to clear codes in the PCM then see if what you did worked..... if you dont clear and reset PCM it will never work.... if it still does not work after all that, most likely the PCM has a problem on the ground side also to regualte the evap solenoid......... If you accidently ran 12 volts + to the ground side of the solenoid plugged in the PCM is cooked for sure........

DRB 2 makes short work of diagnoising the EVP solenoid, you can activate it and test for 12 volts to it and if the PCM is turning on and off the ground to the solenoid.....

 

[mindless]

What I did first was just a test light key on and running got nothing. Wired a ground straight to battery key on running nothing put 12v to it key on running nothing did both power and ground solenoid would click. Tested power at pcm and nothing there.

Also when I cleared code if I left key on and started no cel but if I key off and key back on code is back with out even starting it up.

 

[Rags]

If your wires are good and you tested from solenoid to PCM for opens or shorts,and the solenoid clicks with seperate wires for power and ground, It seems to point to the PCM......... I recommend you replace the solenoid also when you replace the PCM for added piece of mind......

 

[O-Gauge Steamer]

Generally speaking, power is applied to the device and the PCM supplies the ground to complete the circuit.

As a rule...

 

[mindless]

OK thanks for the help guys i have a lead on a PCM from a couple places local, one place has one instock for $65 another place says they have a 96 coming in and only charges $20 for any vehicle computer and another yard said they think they have one on the shelf. So i should have something soon to make sure.

Also i forgot this part this all started after a wheeling trip that ended with me on my side in a ditch haha, not sure if that could have anything to do with it but i think the PCM is the culprit either way.

 

[Tim_MN]

1996 PCM only interchanges with 1996. Why would assume that the PCM is the cause of the P0443 CEL code ?


P0443 JEEP - EVAP Purge Control Circuit

Possible causes
- Evaporative Emission (EVAP) Purge Solenoid Control wire harness is open or shorted
- Evaporative Emission (EVAP) Purge Solenoid Control circuit poor electrical connection
- Faulty Evaporative Emission (EVAP) Purge Solenoid Control

When is the code detected ?
When an improper voltage signal is sent to Engine Control Module (ECM/PCM) through the valve.

 

[mindless]

Well I have replaced solenoid hard wired power and ground rewired from pcm to solenoid all with no luck so what do you suggest I do next??

Code is detected at key on before starting.

 

[Rags]

Did you try a replacement PCM before you wired stuff?

 

[Rags]

Do you have a pic of the wiring diagram for your 1996? I dont have an FSM for that year......

 

[mindless]

I havent had a chance to get my hands on a replacement PCM yet. And no i dont have a FSM either ive been searching the internet for something with no luck.

 

[mindless]

O and Rags my response from this morning was to Tim, I havent had much time for the jeep the past few day. Thanks for all the help you have given so far ill report back once i get my hands on a PCM this week is just a nightmare for me haha lucky the jeep isnt my only vehicle so it can sit for a bit.

 

[kastein]

The 96 ECU is one of a kind unless you have the ability to flash them, in which case most 96 or later jeep ECUs should reflash to be a 96 one just fine iirc.

As for the evap purge solenoid - it's covered in section 8W-30 of my 96 FSM, page 10. Wiring is:

* circuit A0 (red) from battery positive terminal -> fuse 8 in PDC (60A) -> circuit A1 (red) -> ignition switch input -> ignition switch start/run terminal -> circuit A21 (dark blue) -> fuse 18 in PDC (15A) -> circuit F12 (dark blue / white) -> evap/purge solenoid -> circuit K52 (pink / black) -> ECU cavity C20 in connector C165.

So yes, it's powered via a wire from a fuse and turned on via a ground-switch line from the ECU. This is generally how most automotive stuff is done, as ground-switch circuitry is cheaper, simpler, and more durable (n-channel MOSFETs vs p-channel, and ground referenced gate control vs charge-pump circuitry being required.) In fact the only example I can think of on the XJ that's positive switched directly by a computerized device is the AW4 shifter solenoids, all 3 of them are positive side switched. Most other positive side switched items in the XJ are relay controlled, with the relay coils being negative side switched by the ECU.