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The fact that this was not happening with the previous PCM leads me to believe the current unit is also not working properly. The reason I say that is because both HO and regular engines have MAP sensors; therefore if there was a problem with the MAP circuit, code P0108 would have been present with both computers.
As you remember, I first came in to the conversation at the point where the main issue was a wrong PCM part number. The reason I'm saying this now is because, at that time I assumed someone had previously diagnosed the problem as being a bad PCM. Did that in fact happen, or has my assumption come back to bite me in the rear? ;-0
I can certainly upload the pertinent engine performance wiring diagram for you, however that might not solve your issue. Also, Autozone employs people who sell parts, not qualified technicians who know how to diagnose and repair cars. If someone in the Autozone store is saying that you need to verify circuit integrity before they can exchange the PCM or refund your money, tell them you will as soon as that person shows you his/her ASE L1 certification.
I think we have a couple of different needs here:
I'm sorry if you misunderstand my statements and purpose. My goal is to help you solve your issue, not engage in any kind of debate or contest to see who knows more.
Being myself a retired Chrysler Master Technician, I would encourage you to go to your local Jeep dealer and ask them what's the correct PCM/SBEC part number for your application as they might have a supercesion that I'm not aware of. Look at this way, it won't cost you anything and at least will ensure you get the right part regardless of your choice of supplier.
Back to the issue at hand, the computer learns engine vacuum value by interpreting an input signal from the MAP sensor. If the sensor is disconnected, the computer will look at other sensors to try to keep the engine running and set code P0108 as it "sees" no change to the 5 volt reference signal it sent to the sensor.
In reading your last post, I notice that you consider the information I provide as "semi-reliable". As a former professor of Automotive Technology at JS Reynolds CC, and Senior Technician Trainer for the largest used car retailer in the world I assure you it doesn't get more reliable than this. However, if you so desire, I will opt out and re-open your question to the field. How would you like to proceed?
In case you haven't noticed, I've got an ego the size of Mount Everest - which makes my opinion on technical matters anything but humble ;-). However, as luck will have it, we won't have to rely on such opinion because it is a matter of record that Chrysler uses letters at the end of some part numbers to indicate a certain production batch or software release that fits a particular application - as per my database (circa 2009), the AD designation fits your specific vehicle.
Many of these AD units are still available for sale by several outlets that advertise on the internet. However, if you wish to know if there are any SBECs that supersed the AD, only the Jeep dealer can answer that.
In addition, I'll be sure to upload a wiring diagram for you tomorrow after 2PM ET.
That should definitely answer your question regarding the PCM. Once you have the right PCM/SBEC plugged in, I'll be more than happy to answer any other inquiries you have concerning this driveability issue.
Wiring diagrams attached as promised.
Just found the latest SBEC release for yor GC:
Supersedes: 56044810AD, 56044810AG, 56044810AH, 56044810AI
Autozone part number: 79-4810V
The voltage at the Dark Green/Red wire is the signal return wire and should read 0 Volts with the MAP disconnected. The fact that is reading 5 volts tells me that either the return and reference signals are shorted together somewhere in the harness, or the 4th PCM/SBEC is internally shorted. Disconnect PCM (C1 connector) an MAP, then check continuity at the MAP connector between the Orange and the DkGreen/Red wires. If there is continuity (0.00 Ohms), the short is indeed in the harness. However, if there is no continuity (open circuit), then the PCM is internally shorted.
Repairing that short should take care of the P0108, then we can take it from there.
There has to be either continuity or high resistance/open circuit between the Orange and the DkGreen/Red wires. Continuity is the opposite of high resistance. In other words, if you look at your Ohmmeter screen, when both Ohmmeter probes touch, whatever the reading means continuity; when you pull the probes apart, whatever the reading means OPEN CIRCUIT. I don't mean to belittle you in any way, but if there is any doubt as to how to set the Ohmmeter to test these circuits, please give me the brand and model number and I'll help you set it the correct way.
Uh, oh... Wife just informed me I'm not supposed to work on Sundays! Will log back in tomorrow after 2PM ET.
Just wanted to check and see how things are going with that Jeep.
With all due respect, I can't see where semantics are involved in my offer to help you understand how to use an Ohmmeter to diagnose this issue.
In any case, I really want to help you, but can only do so if you do the procedures I indicate and provide me with the information I request. For example, I recommended doing the following: "Disconnect PCM (C1 connector) an MAP, then check continuity at the MAP connector between the Orange and the DkGreen/Red wires. If there is continuity (0.00 Ohms), the short is indeed in the harness. However, if there is no continuity (open circuit); then the PCM is internally shorted"; to which you replied "With cam, crank, map, and tps sensors disconnected, there is no continuity or high resistance between the Orange (5v sensor voltage) and the dk. Green w/ red stripe map sensor wire." As you can see, your reply still doesn't tell me whether or not the PCM connector C1 was disconnected; or what the resistance value was as shown on the Ohmmeter screen. Can you provide that information?
Once again you don't provide me with the information I specifically requested; i.e., was the PCM C1 connector disconnected when resistance was measured between the Orange and the Dk Green wires? what was the resistance value shown on the meter?. Would you rather I opt out and re-open the question so other experts can try to help you?
The truth is that I am just a Master Technician - one of about 300,000 in the USA - who is trying to help you solve your car issue.
Back to that issue; with ignition off and C1 connector disconnected, measure resistance between PCM/SBEC terminals 17 and 27. If continuity is shown, then the PCM is bad and installing it will result in the same problem with the MAP sensor.
With C1 disconnected, it should show "OL" (or same as what the Ohmmeter reads when probes are not touching anything) between terminals 17 and 27.
If the new SBEC/PCM still gives you the same bad running condition and the same code P0108, then yes, it is also bad.
I've never experienced this situation before where multiple PCMs all test bad. I'm going to opt out and re-open the question so other experts can chime in. Please don't reply until another expert responds or the site will revert the question to me.