Bad coil pack?

 

I have tried this and changed twice

 

Changing the fuel pump because of the regulator? The fuel pressure regulator sits inside the external fuel filter, not in the pump.
Does the engine seem to misfire, or does it only show the codes? It is known that a bad TPS can generate an electrical noise signal which the PCM mistakingly can interpret as a misfire .

 

Changing the fuel pump because of the regulator? The fuel pressure regulator sits inside the external fuel filter, not in the pump.
Does the engine seem to misfire, or does it only show the codes? It is known that a bad TPS can generate an electrical noise signal which the PCM mistakingly can interpret as a misfire .

No it is a misfire and I get the codes, I feel the misfire. Ty though

 

What about plugs and wires?

 

A complete tune up was done twice

 

Does it blow smoke at all whether its blue or white?

 

No it does not even when I got the system cleaned out.

 

You said it happens after 50mph. So I am assuming the engine is warmed up and the issue presents itself on a warm engine versus a cold one.

 

yes your assumption is correct

 

I have been checking those as well

 

There is a TSB regarding multiple cylinder misfires due to sticking valves. The valves can stick due to carbon buildup on the valve stems. Can not attach anything now, but have a look at the TSB's at WJJeeps.com - Jeep Grand Cherokee WJ 1999-2004.
They use some mopar cleaner, but seafoam or alike could help.
If that doesn't help, i would swap the injectors from cylinders 1 and 6 with an other position and see if the misfire follows. Worst case could be the PCM.

 

I am having this same issue on my '04 4.0. I am getting the misfire in cylinder #1. Changed plugs, injectors, and coil pack. At 45-50 mph when I touch the gas it acts up, can feel the misfire. Running out of other things to try short of taking it to a shop. Any ideas?

 

Welcome to the garage.
Did you already try a seafoam treatment? Sticking valves due to carbon buildup can be your problem.

 

I fought this same war all summer. Had a professional mechanic working on it with me. Tried EVERYTHING...no dice. Even tried a new ECU. My problem ended up being the valvetrain. I had the head sent to a machine shop and gone over and not a single problem since. My symptoms were identical to yours. I went over ignition, fuel injection, ECU, spark plugs, coil, etc. etc. etc. even had compression checked, etc. Nothing solved the issue so I finally pulled the head and BINGO the valves needed work.

Good luck.

 

I have virtually the same issue with my '02 4.0. I have a 1494or 1495, I can't recall which one but it's the purge valve not responding or faulty or something.
It starts and runs fine but at high way speeds if I get off the throttle just a bit such as going down hill the check engine will start flashing. If I get back on the gas the light will go out and all is well but if I stay off the throttle it will start to miss, but if I momentarily turn the ignition off it will run fine and the light will stay on. It will then show codes PO300, PO301 and PO306.
I'm assuming that it's a vacuum leak associated with the purge valve.

Bugs

 

vlilley, did you find a resolution for your problem? My daughters Jeep has same issue and I have spent a lot of money and thrown a lot of parts at this thing. Soon as it warms up and I let the RPM's drop i feel cylinder 1 and 6 start to misfire.

Any help would be so appreciated

 

Did you already do a compression check on all cylinders?

 

Compression is good unless something changes at higher rpm's. What I don't get is what triggers either the spark or fuel to shut off to those two cylinders. It is almost like a limp mode but I know that applies to tranny issues. If I shut it off it "resets" for a bit. Seems like something is messing with the computer and since it is when it is warm I am thinking a failed component. Is there a way (difficult with the coil rail) to check to see if it is spark or fuel that is getting shut off? It is a very consistent misfire when it occurs - clearly no participation by cylinders 1 and 6.

 

Was wondering if this was ever resolved, my niece has a 2001 JGC with the 4.0 and I had the same issues going on with it. I did the tune up on it and tried a used coil pack I had laying around and it went from missing on #1 and #6 to missing on #4. Put the old coil pack back on it and it would run good for a few mins and the #1 and #6 injectors would quit firing. #6 would quit first the #1 would follow. I had an extra TPS from a 2000 JGC 4.0 so I swapped that out and to my surprise it started running on all 6 again. That was way back before thanksgiving and as far as I know it is still running good. It was mentioned earlier in this forum to try the TPS and it doesn't make since but I was out of options myself and I had the intake off of my 2000 so it was worth a try and only took a few mins to swap. Like I said my niece's jeep has over 300,000 miles on it and I was afraid it was due to low compression or just being worn out but the TPS actually fixed it. I had the engine out of my 2000 and had to buy a new TPS for it when I put it all back together but oh well. Got one from amazon for like 75 bucks for a mopar sensor. Always buy mopar sensor's for these jeeps, they don't like aftermarket sensors!!!!

 

Jeepyard, I am amazed how similar your issue is to mine! I wish a TPS had fixed it - I tried. I think I will have to plan on removing the head and getting a valve job. It seems so counter-intuitive because it runs so well when it isn't misfiring and when it starts misfiring it is not a sporadic misfire and when I cycle the ignition it "cures" the issue for a short while. Thanks for your input. Didi I mention I have a cheap Jeep for sale?

 

Did you try a seafoam treatment through the brake vacuum line? Carbon buildup on the valve stems can make them stick and cause misfires