USNJacket

I have a 2006 Jeep Grand Cherokee Laredo 6 Cyl. 3.7L.

I got a check engine light the other day with a fault code of cylinder 4 misfire. I figured that I hadn't replaced the plugs in about 40K miles so I put a new set in and gapped them correctly.

After that the fault was still in on the same cylinder so I replaced the coil.

Still no joy.

I can hear that the cylinder isn't firing, I even pulled the wire clip off of the coil while the engine was running and I didn't hear any difference on 4.

All of the other cylinders produced a noticeable change in engine sound when I performed the same test.

I checked the forums and only found mostly issues with plugs and coils.

I ran fuel injector cleaner through the system and that didn't help.

Where should I go from here?

Any thoughts would be helpful and if you could point me in the way of directions on how to perform any repairs that would be much appreciated. I am good at following directions but I have limited experience on this model.

Thanks!

dnuccio

first id check if theres power going to the coil. not sure how much it should be though. if that checks out good, id start looking at the injector for that cylinder

Willys55

the 3.7L is prone to excessive carbon buildup on the valves causing it to stick slightly open, lowering combustion in that cylinder. The manufacturer suggests running top engine cleaner, or what is know as intake system cleaner through the system to break up the carbon and clear it out. The other possible cause is weak valve springs, but not nearly as common with this engine.

Willys55

unfortunately both these situations would cause a CEL to illuminate and a corresponding code to be set.

USNJacket

I checked the voltage going to the coil and the resistance of the fuel injector. Both are equal to other values I found on the internet and the value of the other cylinders.

I used a product called Gumout on my last fill up to try to clean out the system and that didn't work.

Do I need to use a different kind of cleaner? If so what would you recommend?

I also followed the instructions and added it to a full tank of gas, would it help if I did it on a half tank?

KF2M

What did the spark plug look like after you pulled it? Was it all carboned up, oily, clean? Did it reek of oil, or fuel?

USNJacket

It was relatively clean, it was just worn, there weren't any carbon deposits or oil. I replaced them about a week ago so I don't remember any fuel or oil smell.

tiwvr1

Check compression, Check for spark (pull coil and crank it with a plug grounded and check for spark) If you have compression and spark it is most likely a injector or injector wiring. Simple...

USNJacket

Compression came out to 100 PSI on the cylinder. Spark was good. I also ran another can of seafoam through it.

I pulled the valve cover to have a look and didn't see anything obvious but I am in territory that I don't really know.

tiwvr1

That low of a compression will cause a misfire, at least a noticible one, u prob dont feel it much when u drive, just at idle mainly right?

USNJacket

I only notice it when I am idling, correct.

alwaysxj

Did you find out what was wrong? My wife has a 06 and cylinder 1 is misfiring. I did plugs and coil, still doing it. I am at a lose. Some help would be great!

dnuccio

100psi is pretty low, what did the others measure?

MichiganCherokee

I have the same thing going on with my 01 XJ. Cylinder #1. I'm assuming it's something to do with wiring. I've replaced the cylinder head, compression is 160-165 on all 6. All new injectors new plugs, new coil pack. Dealer said it's only showing a misfire at idle, which you can feel it shutter, driving it runs smooth. Not sure where to go next.....

dave1123

This may not have anything to do with your problem, but a friend if mine had a remote start unit put in his Saturn. he had a cylinder not firing and he took it back to the guys who installed the remote starter. When they drilled a hole in the firewall, they nicked the wiring for the injectors so it wasn't firing. Maybe the problem is with the wiring to that injector. You've got to check to see if you're getting an impulse to that injector. There is a thing called a "noid" light that plugs into the harness at the injector. You can probably borrow or rent one at Advance Auto.