Hersch

Okay, your explanation takes me back to the belief it is electrical. Wish I could put spark testers directly on the plugs. Anyway, per a previous post recommendation, I worked on the battery and actually ended up putting a good used battery in. Seems after a few days, the engine isn't turning over as well, just like before. I also noticed at low RPM's the cabin lights flicker a good bit even when engine is running well. I had read elsewhere that a battery/alternator problem could cause the computer to shut off a coil. The alternator is working but perhaps has an issue. Thoughts? This would also explain why it starts to misfire at low rpm perhaps? Whatever causes the misfire, it does "reset" after I shut the engine off and restart.

dave1123

Okay, there is one other small item you can check. Underneath the battery, there is a temperature sensor that the PCM uses to monitor the battery. When it battery gets hot, it cuts down the alternator charge rate. This is just a thermistor, or temperature variable resistor. The PCM uses this data for other things, most of which elude me at the moment, but does come into play for starting monitor sweeps, like controlling the canister purge solenoid cycle and leak detection pump.

It looks like a small round button in the center of the battery tray and can be changed by prying it out, pulling it up, and disconnecting the wire connector. I believe the resistance value should be 9K to 11K ohms at 75-80* F.

Hersch

I checked the battery temp sensor - It seemed to give the right ohm readings but I may just buy one so I can rule that out. When we bought the jeep it had an extremely dead battery. Driving it didn't seem to charge it very well, though the voltage when running was 14.08 or so. I worked on the battery terminals and put a new battery in. In a few days of sitting the battery was completely dead again. I cut the original terminals off and put new terminals on because I had read about corrosion inside the terminal itself causing problems. . . So I have a parasitic draw and after reading about the computer being sensitive to voltage fluctuations wonder if that also causes the computer to somehow shut down 1 and 6.

Regardless of the connection with my "main problem" I am going to pursue this because there may be a connection.

What is the best way to check for source of draw. I know I can pull fuses but is there a standard ohm measurement for the hot and ground when disconnected? SHould I unplug fuses and watch for a voltage increase? I have a fluke meter but I don't think it has any way to check amperage.

THANKS!

Hersch

Thanks everyone for their help!! I wish I could happily report the problem solved but I have had the vehicle in the shop to check the vacuum system - they said it checked out. I have replaced every electrical component and reworked many connections. It looks like I will be removing the head and getting a valve job done. Just seems so odd that it runs so well then goes into a very clear "misfire mode". Cycling the key then clears up the issue for a short time. Did I mention I have a nice 01 JGC for sale cheap?

dave1123

I seriously doubt the valves are burnt. I'd say it's more likely carbon buildup inside the cylinders. Mopar makes a special carbon removal treatment OR you can try using Seafoam. Jeep has a Factory Service Bulletin on carbon buildup in the 4.0. Basically it says the 4.0 is known for carbon buildup in engines that are constantly run below 2000 rpm. IDK about you, but 65 mph is only 2100 on my tach! Are they telling us to punch it more often? If the spirit moves me, I sometimes run in 3rd gear for 5 miles or so on the highway.

BTW, my 2000 WJ 4.0 started life in Washington, PA.