Multiple injector misfire codes

[southernwake]

Driving back from Philly tonight and about 20 minutes from the house the check engine light blinked 4 times and then stayed on. Got home and checked the codes and I am getting the following:

P0300- misfire multiple cylinders
P0303- misfire cylinder 3
P0306- misfire cylinder 6

I did a quick search and found it could be anything from coil pack, to plug to low compression on those cylinders.

A few months ago I replaced all spark plugs with the correct manufacturer recommended plugs. I also replaced all the coil packs. ( I still have the ones that were on there so I can throw those back on and see if those two cylinders throw the code again)

I am in a bad position here, because I am supposed to be moving here in a few days, from PA to TN, and was going to use the jeep to haul a small pull behind uHaul.

It seems to be idling fine ( its hard for me to be sure here, I have been driving a rental car for a few weeks for work and havent driven the jeep much, it has a rougher idle than the car I was driving but it doesnt idle like its missing a cylinder like I have had experienced in other cars before) no issues accelerating or loss of power while we were driving it. Once I got home and shut it off and let it sit for about 15 minutes I started it up and I did notice the exhaust smelled rich.

Aside from me switching out the coil packs with the old ones to see if the codes go away, what else can you guys suggest I check? I dont have my compression tester with me in PA. If I cant get it resolved tomorrow or early Monday I am going to have to be at the mercy of the dealership as I need to have the jeep running 100% for this trip.

2003 Liberty Renegade, auto, 123320 miles.

Thanks
Andrew

 

[renegade 04]

First check to see if your battery is okay and then make sure the connections on the battery are clean and tight. Second see what the voltage is when the jeep is on and about 1 hour after the jeep was running to see if your problem maybe with the charging system. I would also try using some fuel injector cleaner in your next tank of gas and see if it helps.

 

[southernwake]

I saw that a few people suggested the battery connections when I was doing some more research. A couple weeks ago when I was changing the thermostat due to a "engine cold for too long" code due to a aftermarket thermo, I disconnected the battery while I was working on it. So possible that maybe one of the terminal connectors is loose. I will check the voltage too.

I have been researching injector/top end cleaners as well.
I have some things to check and a starting point.

Thanks
Andrew

 

[tjkj2002]

Swap in known good coil packs and see if the misfire codes return.A bad battery/loose battery connections is not a concern with misfire codes.Another possible cause is the cats going out but have yet to throw a P0420/P0430 codes,I have run into this issue a few times on KJ's with the 3.7.

 

[southernwake]

The first thing I plan to do in the morning is swap out those coil packs and see what happens. Cheapest and easiest thing to do since I still have the old ones.

Thanks
Andrew

 

[Phil + Neela]

I had the P0300 happen as well along with the blinking orange triangle (severe catalytic converter damage possible). I checked the coils, changed the plugs, verified connections, etc...until finally giving up and taking it in. They tried a whole slew of things and failed before listening to what I had to say... We were able to figure out that the upstream O2 sensors were bad, but feeding enough voltage to pass the test and not throw a code. This made it run really rich as that is the "default" for the computer and caused the misfires.

Bottom line, check your O2 sensors if injector cleaner doesn't do the trick.


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[southernwake]

Yesterday I swapped out the coils with known good coils and cleared the code and drove it around town to do some errands. I also bought some injector cleaner and put that in the tank. I haven't had the codes come back up. I will keep an eye on it and hopefully it wont come back.

Thanks for the help!
Andrew