used PCM replacement basics? - JeepForum.com
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post #1 of 18 Old 05-22-2020, 03:24 PM Thread Starter
CheyneEaddy
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used PCM replacement basics?

Hello can anyone tell me the basics of replacing a factory PCM with a used PCM. I understand the same model and numbers etc.. have to match with new PCM, but is there a sticky about this like what I have to do to get the vehicle to run correctly as it was, and what to NOT do.

Thanks, Cheyne

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post #2 of 18 Old 05-22-2020, 04:00 PM
jtec
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I gotta ask What makes you feel the PCM is bad?

Also can you program PCM's often VIN, milage etc?

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #3 of 18 Old 05-22-2020, 05:10 PM Thread Starter
CheyneEaddy
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If you read my previous thread, I have a problem with cylinder 7 injector open circuit. I have done everything but replace pcm.
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post #4 of 18 Old 05-22-2020, 05:11 PM Thread Starter
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dealer did a compression test and was 180 psi and 3% leakage, so no fallen valve seat...
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post #5 of 18 Old Yesterday, 05:44 AM
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Is the electrical ground signal coming out of the PCM? If yes, then it is not the pcm.
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post #6 of 18 Old Yesterday, 07:00 AM Thread Starter
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How do I tell? are you asking if the pinout for that injector control is coming from the PCM? 5 K26 16 BR/YL INJECTOR CONTROL NO. 7
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post #7 of 18 Old Yesterday, 07:18 AM Thread Starter
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Do you think a failing crankshaft or camshaft sensor would be causing a misfire in cylinder 7?
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post #8 of 18 Old Yesterday, 10:52 AM
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If you know it is an injector open circuit, that is what I would hunt down first. You can test it with a noid light on that injector. Or, you can use a test light at the pcm and see if the ground signal for cylinder #7 is leaving the pcm.

You mentioned that you tested everything else. What exactly did you test?
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post #9 of 18 Old Yesterday, 11:38 AM
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Did the dealer trouble shot the inj issue or they did compression test for another reason?

The injector is a 2 wire circuit, one wire is common to all ijectors the 12v supply, the other is specific to each injector and is the driver - the PCM will ground the driver when it wants the injector to spray.
The PCM also monitors the voltage on the driver circuit, it will set a code p020x if there is a problem with driver circuit.

Are there any codes?
Is there 12v at injector?
Did you try a noid light on injector?

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #10 of 18 Old Yesterday, 03:47 PM Thread Starter
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P0207,p0307,p0171
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post #11 of 18 Old Yesterday, 03:50 PM Thread Starter
CheyneEaddy
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I used a test light on pinout 5 C1 which is ground for inj. 7 and there is a little light, not bright.
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post #12 of 18 Old Yesterday, 06:25 PM Thread Starter
CheyneEaddy
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Checked again and it was bright this time.
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post #13 of 18 Old Today, 12:48 AM
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sounds like you should check the wire from PCM to inj, a bad connection, damaged wire.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #14 of 18 Old Today, 05:05 AM
RCS1300
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Quote:
Originally Posted by jtec View Post
sounds like you should check the wire from PCM to inj, a bad connection, damaged wire.
+1

Assuming the PCM pin you tested was the correct one, it proves the problem is between the pcm and the injector in cylinder #7. It could be the wiring, the connector at the injector, or the injector. I would first follow the wiring from the pcm to the #7 injector and perform a physical inspection. Look especially close at areas along the wire that are exposed to vibration or heat.

Also, I would use the same test light and see if the electrical signal from the pcm is coming to the #7 cylinder injector connector. Also see if you have 12v of power at the injector connector pin. If there is power at the injector connector pin and the ground signal is reaching the injector connector, the problem is your injector.
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post #15 of 18 Old Today, 06:06 AM Thread Starter
CheyneEaddy
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Just ran a separate wire from pcm to injector, still not working. I cut as close as I could to pcm wire harness cause I do not know how to take wire out of pcm harness.
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