ECU problems and replacement

[jota320]

Hi there, has anyone had problems with their KJ PCM/ECU? I was told today that I need to change it once again, this would be the third time, for some reason the PCM/ECU kills the current to one of the coils, I have changed other things before that I was told caused the short circuit, so I'm either the unluckiest out there or it is a known issue with the PCM/ECU, if it is a known issue and there is a permanent fix let me know, if not then I guess I'll have to call it quits and buy another car, I love my Libby though. Thanks in advance for any feedback.

 

[tjkj2002]

Not common at all.

The automotive PCM/ECU rarely fails.

Something is causing the failures,could be bad reman PCM since that is a common issue.

 

[Billwill]

Is it always the same coil that has the problem?
If so then replace that coil with a new one and carefully trace the wiring going to that coil all the way from the PCM to check if that wiring is chafing to chassis/engine somewhere.

If it is a different coil every time then likewise carefully manually trace the wiring to each coil to make sure that they are not chaffing to chassis/engine somewhere.

With the battery disconnected, unplug all the connectors on the PCM and unplug the connectors at every coil. Now these wires should be floating ie. not going anywhere.
Get a Digital Multi meter, place it on the Ohms setting and measure each of these wires to chassis and to each other to see if there is any form of short...the reading should be a lot of Ohms ie. a few Mega Ohms in other words no short. If it shows a few Ohms ie. 1 ohm to 1,000 Ohms then there is a short or partial short to chassis.

Make sure you are not touching the meter leads with your bare hands while doing this measurement or you will pick up the resistance of the current flowing through your body.

Do all of this before replacing the PCM again...you have to find the short and fix it or else you will blow another PCM.

 

[jota320]

Thanks

Thanks will do as advised, in the case I have a wiring issue, can you point me to where I can buy the wiring harness?, maybe I should just change the whole wiring.

 

[Billwill]

Thanks will do as advised, in the case I have a wiring issue, can you point me to where I can buy the wiring harness?, maybe I should just change the whole wiring.

Major work to replace the wiring harness....if you find a shorted wire you insulate it. If the wire is disconnected at both ends but you get a resistance reading to chassis which indicates a short to chassis or you get a reading between the two wires going to the coil packs...with both ends disconnected...but you cannot see where in a large harness the problem is then you:

Cut of the bad wires at both ends and insulate both ends off.
Replace the wires with new ones of the same gauge (thickness)...the colors do not matter. Solder the wires into place at both ends...take the shortest cut...and insulate them. Make a note of what changes you have made in the correct page of the wiring diagram for the next owner after you.

You can download the KJ Service Manual here for your year KJ...includes Wiring diagram. The 2004 KJ is not covered so the 2003 is the next best if you have a 2004 KJ.

Index of /manuals/Jeep/KJ

 

[Rowlette]

Thank you my friend, That link is very helpful.[emoji4]

 

[FranzKK]

Hi there, has anyone had problems with their KJ PCM/ECU? I was told today that I need to change it once again, this would be the third time, for some reason the PCM/ECU kills the current to one of the coils, I have changed other things before that I was told caused the short circuit, so I'm either the unluckiest out there or it is a known issue with the PCM/ECU, if it is a known issue and there is a permanent fix let me know, if not then I guess I'll have to call it quits and buy another car, I love my Libby though. Thanks in advance for any feedback.

If by chance you still have this account-- what was the cause for the short burning out the PCM? I am now experiencing this single coil #6 burnout for the second time, and will soon find out if it also burned the PCM again.