Codes just indicate miss on one and six. AFAIK, the vehicle is stock. Several garages have looked at it and came up with zip other than what's been done so far. Best guess now is a "wiring" problem." The Jeep has been setting on a dealer lot for two years. I suspect it's something weird that defaults to the, "Use known good parts to diagnose" or an offbeat wiring issue that may require a tough to accomplish right time, right knowledge at the same time to catch.
it is intermittent ? I still would suggest the scan - its free and fast. UNLESS you have a scanner? I would suspect a p0351 type coil code.
As the codes are po301 and p0306 it suggests to me a coil issue as they are the paired coils.
You could remove coil, look at plugs, check the coil to plug insulators springs etc, check the harness as it plugs into coil the wire for #1 and 6 may have a break and that's often seen in first several inches of connector, check the pin as it crimps on terminal and spray some 'deoxit' on all contacts.
I have no idea how much it was run after all of the garages "fixed" it. I know the dealer sold it and had to buy it back. I got the impression it had been to several garages. I noticed it setting several months ago. Today was the first time I found the owner out front as I drove by.
If so, it looks like one of those "waste spark" systems, where one cylinder on its power stroke, and the one opposite it in the Firing Order, BOTH get sparked. One needs it, the other doesn't and doesn't care. So normally I'd say one coil of this three-coil assembly is bad. But you say you have a Known Good one. How are the connections between that Coil Assembly, and the system that's controlling it?
I haven't done anything to check the Jeep other than think about an offer. The dealer wants to get rid of it. The body and interior look good. Right now, I'm going to let it set. I may check under the hood later. I'm in no hurry. I've got beau coup work to do on my own stuff before getting serious about the jeep. The missus also wants the sub frame and rack and pinion replaced on her Honda first. ;-)
I appreciate the suggestions. You folks have always been top notch.
Actually, Dan can be no closer to the truth on this one. But from memory, it was not stronger springs for the 2000's or so, just to check if the valves could rotate.
Try a Mopar combustion chamber treatment first. It may help before delving into the exhaust valve springs which may be closing too slowly. Here is a TSB referring to this. Back when I was working for mopar in the 2000's, this was a regular and easy fix. Rotation of each exhaust vale may be necessary.
Rebuilding a Honda... I wish I could remember where I saw it. Wasn't looking, but I ran across a "kit" for Honda that was two upper wishbone arms with the upper ball joints, two lower ball joints, inner and outer tie rod ends, and they said but I didn't see in picture, sway bar bushings. ALL for less than $100!
Only FWD rack and pinion I've changed was on a GM "A" body (Buick Century) and it was really easy once I found I could drop the rear end of the sub frame. This idea emboldened me to replace the camshaft in that Buick (3.0 V6, 3.8 family) by dropping the passenger side of the sub frame. I don't think it'd be hard to change out a sub frame with stands behind it right on the unibody, then a wooden fixture to support the power train from the top. Maybe using the shock towers or fender well edges for support...
We found that carbonizing before rotating the valves worked more than half the time hence we cut down on work warranty time by more than half. So my idea is to try a good old mopar treatement first. You may just find that multiple misfire go away on it's own after that. Certainly worth a try and not time consuming since you have that honda to work on.
Of note, there are two ways to use Mopars combustion chamber fluid to kill two birds with one stone. One is to de-carbonize via a vacuum on manifold and also by pushing the cleaner through the injector rail.
For the injector rail treatment, you will require a special canister with a pressure regulator and some knowledge of how to cut the fuel pump. Fairly easy, just remove the fuel pump relay. Engine must be hot and preferably with old spark plugs in there. Then when the chambers and valves are clean, and the injectors are cleaned via the pressure cleaner treatment, you then put in new spark plugs. Cuz the de-carbonizing procedure is very hard on plugs, so you want new plugs in there once the overall treatment is done.
I would do both at the same time if you have the equipment. Such treatment kits should be available at your local shop. If they don"t have such equipment, your going to the wrong garage. Such equipment from my experience, cannot be rented out. But if you a car guy, you can buy a kit for cheap for almost the price of one treatment. So if you know you will be using this kit in the future, very handy to have in a tool chest.
This for informational purposes only since this thread reminded me of what we would do back in the day of the 4.0l's and also other various engines. To this day, I have not changed my work ethic and still prefer my own mix of injector cleaner fluid.
Especially with fly by wire systems now, I prefer to have a bidirectional scanner to help me along with the processes. But for this 4.0l, a match book will do the same.
Achieving approx 1500rpm, will prevent the engine from stalling when passing cleaner through manifold for chambers and valves cleaning/de-carbonizing, and at same time, the fuel rail treatment will accomplish itself until there is nothing left in the canister. Always have a scanner ready if you have one to monitor engine temps and cat readings.