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Chris (aka-Moose)
Chris (aka-Moose), Technician
Category: Jeep
Satisfied Customers: 47633
Experience:  16 years of experience
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Cherokee [not Grand]: I have a 2000 Jeep Cherokee [Not Grand]

Customer Question

I have a 2000 Jeep Cherokee [Not Grand] that has been missing. Diagnosis simply says "missing on cylinder 1 then 3 then some other". It runs fine then will miss under load or it will miss when idling and run fine faster. I changed the coil pack [twice]. I got an ECM from a junk yard with the same code on it. The replacement ECM allows the car to start fine but then shuts it off in about 5 seconds every time -- even if I rev the engine. It seems like the junk yard computer runs the engine better for those 5 seconds but then shuts the engine off. I have replaced the fuel pump and the crankshaft position sensor within the last year or so. Why does the junk yard ECM shut the engine off. I do not have a SKIM system or antilock brakes. The Jeep does not burn oil, has 172K. I have treated it well. If you don't have an answer I will not pay you. Thanks. Bim xxxxxx
Submitted: 2 years ago.
Category: Jeep
Expert:  Chris (aka-Moose) replied 2 years ago.
Hello, I'm Chris. Thanks for seeking us for help.
The junk yard PCM can shut down the engine from an internal issue that is shutting down the ASD relay. It can also be seeing an issue like a incorrect coolant temp sensor reading or low oil pressure reading. Do you have a scan tool that can check those 2 readings with the key on, engine off?
You want a excellent 5 star answer & I would like to be rated the same for providing it. Consider I don't know your skill level & I can't see, smell, hear, or touch the vehicle. It may take a few back and forth replies. Try your best to respond with good detail so I can do the same. I normally log in at 3pm and work late. A rating is required. Your rating me, what I type. I am not an employee of this website, nor have control over the fees or the time it took to get a response. If you rate negative or not at all you still paid, but I get nothing. I want you pleased with me and my efforts, so let me know if your experience here has come up short.
Thanks Chris
Customer: replied 2 years ago.
I bought the junk yard ECM several years ago and installed it when my Jeep had been running erratically. I worked fine then but with the same problem. I found the problem was the wiring harness was shorting out on the back of the fuel rail. When I saw that my erratic problems were solved so I reinstalled my original ECM and stored the JY-ECM. Now I am perplexed because the Jeep has been missing some of the time and I haven't been able to put my finger on it. So I reinstalled the JY-ECM and it runs for 5 seconds and shuts down the engine. The original ECM does not shut the engine down but I have the missing problem. I would think that if either the temp sensor reading or oil pressure reading was off, then the original ECM would shut down the engine also. I will see if I can find a way to test those. I may have to take it to a Jeep dealer to test those matters. Why would the Jeep run fine then when I step on the gas at 50 it will miss. I can also miss when idling or at any other speed but then will run fine for a bit? I have also had a problem with charging the battery. It seems that the battery doesn't get fully charged but it usually doesn't get completely down except one time that I could not start it. I was thinking that may be an ECM problem also that might be related.
Expert:  Chris (aka-Moose) replied 2 years ago.
The way your wanting to diagnose this is not something I am going to be able to work with, being it does not following along with what I would do. I think its bet I let another try to help.
Customer: replied 2 years ago.