Wiring harness

[aidanm]

Hi all,
So I’ve been having a p0306 code for I don’t even know how long as this point and I’ve tried everything to the point it’s only come down to wiring and I was wondering if anybody knew any key locations I should start? I’ve switched injectors between #5 and #6, changed spark plugs 3 times, changed coil rails, done a compression test, done a leak down test, done a fuel pressure test, and everything came back fine. Thanks!

 

[AndyG]

A friend of mine has a lot of his pulled right now-

I’m really not answering your question but I want to validate your question-

I’m starting to notice that heat and of course any kind of vibration and abrasion will eventually degrade the harness-

I’m starting to be of the mind that being willing to maintain the harnesses is part of the future of TJ ownership.

The first thing that seems to happen is the factory loom gets brittle and basically falls apart- then it is exposed wire.

Also I have one rig that @mrblaine did some work on and I noticed that he was meticulous to make sure the harness stayed out of danger.

He has more tricks than a $2 hooker, and has seen all kinds of failures.

I wish I knew more to tell you and definitely want you to solve the problem.

This is a little bit rare but if the PCM has been unplugged it doesn’t hurt to look in the plugs, they are actually the female part of the assembly, and see if any of the receivers have fell back into the housing.

I have some diagrams that show you what wire has what function-

One part of the harness assembly that concerns me is the oxygen sensor wire that runs behind the engine - not that its a player in this issue but it sure gets hot.

On a 2005 its an 18 gauge wire, brown and violet, that controls injector 6 and goes to the 2nd plug from the left on the pcm, facing the plug it is the top row, 4th from right.

I know yours is older but this will at least give you an idea of the kind of information you’re looking for- Mark @Wranglerfix can get better year specific data.

 

[aidanm]

A friend of mine has a lot of his pulled right now-

I’m really not answering your question but I want to validate your question-

I’m starting to notice that heat and of course any kind of vibration and abrasion will eventually degrade the harness-

I’m starting to be of the mind that being willing to maintain the harnesses is part of the future of TJ ownership.

The first thing that seems to happen is the factory loom gets brittle and basically falls apart- then it is exposed wire.

Also I have one rig that @mrblaine did some work on and I noticed that he was meticulous to make sure the harness stayed out of danger.

He has more tricks than a $2 hooker, and has seen all kinds of failures.

I wish I knew more to tell you and definitely want you to solve the problem.

This is a little bit rare but if the PCM has been unplugged it doesn’t hurt to look in the plugs, they are actually the female part of the assembly, and see if any of the receivers have fell back into the housing.

I have some diagrams that show you what wire has what function-

One part of the harness assembly that concerns me is the oxygen sensor wire that runs behind the engine - not that its a player in this issue but it sure gets hot.

On a 2005 its an 18 gauge wire, brown and violet, that controls injector 6 and goes to the 2nd plug from the left on the pcm, facing the plug it is the top row, 4th from right.

I know yours is older but this will at least give you an idea of the kind of information you’re looking for- Mark @Wranglerfix can get better year specific data.

View attachment 549507
View attachment 549508

Sweet thanks!

 

[Wingback73]

Check the back of the engine where the loom goes behind the valve cover. That is a wear point on many vehicles and can cause intermittent failure/codes

 

[hear]

I’m starting to be of the mind that being willing to maintain the harnesses is part of the future of TJ ownership.

Facts.

 

[ItchyDong]

Visual inspections are cool when looking for wiring issues. However, if there is a bare wire touching something, moving the wire harness can temporarily "fix" the issue.

So many electrical issues can accurately be diagnosed with a cheap ass incandescent test light. This problem, being one of them.

Being that it's a single cylinder misfire, I doubt it's coil related being that it's a waste spark system. It would trip two DTC's for it's companion cylinder. Lets focus on fuel circuit integrity

1) With test light connected to battery ground, Key On/Engine off, with a T-pin back probe #6 cylinder injector power wire (Dark Green/Light Green wire). Touch test light to T-pin. Test light should light. If not, find broken wire.

2) With test light connected to battery positive, Key Off/Engine off, with a T-pin back probe #6 cylinder injector control wire (Light Green/Black wire). Touch test light to T-pin. Test light SHOULD NOT light. If it lights, keep touching t-pin to keep light illuminated while wiggling the harness that runs behind the valve cover. When the light goes out or flickers, you've found your short to ground.