guiness_guy

Just picked up the XJ had to take it to a shop. Turns out it was a bad PCM the board had several parts that were fried or missing. They dropped the spare I had in after checking it out and it's running much better but still throwing codes and still have the CEL. I only had them fix the PCM now that I have the proper codes I want to fix her myself.

P0300
P0301
P0306
P0443
P0456
P0442

Everything points to a bad vacuum leak somewhere. I sprayed everything I could find but I'm obviously missing something. I'm going to bust out the book and spray every single vacuum connection and line I can find in the book.

Crazy 8s

You might just replace all your vacuum lines as some of them may be clogged or rotted out. I know that many here would suggest you use the stock vacuum harness, but if money is a concern to you, you can just run bulk hose from point to point for pretty cheap.

captainwoot

Is it running better? just looking at those codes , off the top of my head, p0300 multiple cylinder misfire, p0301 cyl 1 misfire, p0306 cyl 6 misfire
p0456 is a small evaporative emission leak. p0442, 443 are emission related as well i think.

Have you had a chrysler dealer check it? I would suggest checking the cam sensor adjustment, these can de dialed in correctly with the drb111 scanner. then go over all of your vac hoses and connections from front to back (including evap canister under the jeep)

Good luck!

DFlintstone

Latest "news flash". To erase a PCM, just lave the battery disconnected over-night. No harm to have a dome light, (or headlights) on. "Capacitor bleed down" is mentioned. (6 hrs). This will do it. Less might work, but this will. Better to go "all in", in my opinion. "1/2" Reformatting a drive might leave nags.....Idk

(Btw, I did not underline "dome light" it just happened.......

CCKen

My guess is the coil that fires #1 and #6 plugs is defective (P301/P306), or the PCM driver for this coil is defective, or the wiring from the PCM to the coil is defective.

In the waste spark ignition system, plugs are fired in pairs, i.e., 1&6. 5&2, and 3&4.

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Inspect/replace the gas cap for the EVAP codes.

dschappell

Will erasing the PCM reset and clear the misfire code "if" it's the PCM? I'm replacing plugs today and inspecting the lines because in getting misfires on 3 and 4. No other codes though.

dschappell

So if I'm getting codes 303 and 304, cylinders 3 and 4 are misfiring, And so it could be one of the issues you mentioned because it's in that pair set up and I'm getting no other codes.

captainwoot

/\ /\ /\

Agreed but the coil pack and pcm have both been tried / changed...so injector driver circuits.....something in the harness? Just thought it would help to have cam sensor set as i have seen them act up if out of range.
If it doesnt miss all the time it is unlikley a valve problem. A weak valve spring would prob only show at high rpm.

CCKen

I would suspect a bad coil rail, but since you'll have the rail off to replace the plugs, which I hope are NGK ZFR5N or Champion RC12ECC plugs, examine the electrical connector to the coil for corrosion in the pins and pin cavities. Examine the wiring harness for chafing to the wires within the loom. Verify the connectors to the PCM are secure.

If you have an ignition coil capacitor bolted to the right side of the block, near the CMP, disconnect it.

If everything looks okay, reassemble everything, clear the code(s), then, while the engine is running, wiggle the wiring harnesses to see if the same codes pop up, or different codes pop up.

In the long run, see if you can get a coil rail from the junk yard and try it out.

Edit: I overlooked the fact that you changed the coil rail already, so i would suspect wiring or the PCM.

Do the visual checks and wiggle checks.

Verify you are installing the correct plugs for your engine.

Here's what the ignition coil capacitor looks like:

dschappell

Thank you so much!!

CCKen

Revised my previous post. Did you change the coil rail?

dschappell

No I havnt removed anything yet. I have to take the dog to the groomer at 9 so I'm doing it when I get home. I was going to swing by napa and pick up plugs then work on it. I'll post back soon.

CCKen

The CMP for these engines does signal the PCM which cylinder is in firing position for the purpose of driving fuel injectors (only) unlike the in the distributor days where the CMP also gets involved in the PCM driving the ignition coil for the respective plug firing. If his CMP was out of sync I would think the misfiring would be random cylinders, not pairs.

If his CPS wiring were intermittantly shorting out due to chafed wire at the intake manifold (engine movement) it may cause random cylinder misfires.

CCKen

The preferred plugs for the 2000/2001 engine are NGK ZFR5N. I've been told that the dealers are handing out these plugs if you were to go to them for the Champion RC12ECC plugs.

dschappell

I need help. So the jeep doesn't have coil rails. It has the distributor still.