More misfires



we own a 2003 Jeep Liberty Sport, with 75,000 miles on the 3.7L. This thing ran like a top. My wife called me at work and told me that all of a sudden it’s running rough and that when she approached a stop the engine would die.

I work at a tire store, and we have a Gennises Scan tool, mainly to diagnose ABS problems, so I brought it home from work.

The Jeep ran really rough with a drastic drop in power. The scan tool revealed no bad sensors, but It said; A)cylinder 3 misfire, B) cylinder 4 misfire, and C) random misfires. Also the scan tool revealed that the vehicle computer kept adjusting the timing from a value of 0-8 to keep it running at idle. Of course It’s Saturday evening so we dropped it off at the dealership with a short description, a contact number and a request that they contact me for more info. They claimed to call me monday morning before I arrived at work (the number I gave them), I called the dealership monday around noon, and got the service dept voicemail, left a message for them to call me, they didn’t. I was off on tuesday so I stopped in early and they told me that it was with a tech, and that they would get back to me, by afternoon they had not called so I stopped in, by now I owe them $90 and all they can tell me is that it isn’t a sensor, or the fuel filter(which I thought might be plugged) they claimed the fuel press. was normal. I don’t know what else they checked.

Now for the scary part, They told me that they put the info from whatever tests they ran into a computer and the computer tells them the most likely causes. The first and least expensive fix was to pull the valve cover and see if the rocker arm had become loose, this was expected to take another 2 hrs @ $90 per hour, the second more expensive option was to pull the motor apart and see if the exhaust valve was “BAD”. this is the point that I informed them that I had already had the scan tool hooked up and got messages that the #3 and #4 cylinders were misfiring, I didn’t thik it made much sense that the rocker arms for both the #3 and #4 cylinders would “BECOME LOOSE AND JUST NEED TO BE TIGHTENED” at the same time. the person working the desk looked at the paperwoork, pointed and said, “JUST THE #3 CYLINDER IS MISFIREING”, without a second thought, I’m just guessing but if you don’t put the right info in the computer to start with, how can you get the right answer at the end? I’m not looking for any more horror stories, but I’m curious if anyone else has had a similar problem with their jeep or similar engine, and what the fix was.

Now for the worst part, the same saturday we dropped the jeep off, we closed the deal at this same dealership to purchase a New 2009 Dodge Ram 1500 4X4 Quadcab, and they are the ONLY Dodge Dealer in 50 miles!


There are independent garages/mechanics closer than 50 miles. Ask around.
I’m sure that you can get a better diagnosis from an independent (and, a lot cheaper).


It is possible to get misfire codes for #3 and #4, but for only one of them to be really misfiring. The misfire codes that the engine computer generates are only its best guesses based on speed changes of crankshaft rotation. It can be wrong.


Burned valve, all of a sudden? not likely. Loose rocker arm? Na. If they are adjacent cylinders, maybe a head gasket? If they share a coil, bad coil (pak). Someone should get back to basics and not rely on a computer to what’s most likely to happen. A compression check is in order. As well as a visual on the ignition wires, plugs, etc.


thanks for the help,
time for an update. went to the dealer this am first thing. asked exactly what they had tested and what the outcome was yesterday, I was told, “we checked everything external and found no error codes, it’s pointing to the inside of the engine”, there is a coil for each cylinder and they claimed that they took the coil packs off and moved them around and only the #3 cylinder was misfiring.
Against my better judgement, I told them to go ahead with their step one and give me a call, and that I was still concerned with #4 cylinder. They called me hours later, they had the valve cover off and there was nothing wrong with the rocker arm, THEN “since you were concerned with Cylinder 4 we did a compression check and number 4 was at 200psi, and number 3 was at 0 psi”, who the hell wouldn’t check the compression day 1 when the spark plugs were removed to check for fouling.
At this point I told them to put it back together and that THEY were done.
$200 later I picked up the car and asked for a complete list of what they had checked and what the status was, what I got was an invoice with this comment, “completed check, found code misfire #3, check coil good, check plug needed but not problem–checked compression 1 200psi 4 200 psi 3 0—found failure to be in cylinder exhaust valve.”


I have found one to take the jeep to, but that doesn’t help me with the lifetime powertrain warranty on the new truck.


My brother ‘inherited’ a Cherokee with the same problem. My neice couldn’t afford to pay him for all the repairs so she gave it to him. My ever so generous brother didn’t even consider doing it all for FREE - she is a student after all.

If you had a valve failure that was serious enough to allow ALL of the air to escape then you have dropped a valve (a burnt or cracked valve will still compress a little air). This will cause serious problems. If this is the case two things would happen. When running - the broken off valve head would be banging around in the cylinder could be heard by the deaf. Apparently this is not the case so the valve has already punched thru the top of the cylinder and is now laying in the bottom of the oil pan. All of the air is simply whooshing around and doing nothing.

If you want to do some simple tests:

With the engine running remove the oil filler cap- you should be able to hear and feel air whooshing in and out. You can also draing the oil and look for peices in the drain pan. I would also take a peice of wire and bend it so you could feel around for any peices laying in the pan.

Pull the spark plug, turn the engine to get the cylinder to TDC on the compression stroke, take an air hose nozzle and wrap a wrag around the tip. Stuff this into the spark plug hole and press the nozzle button. If this is the case the air can be heard escaping thru the exhaust pipe and the oil filler hole.

If you really want to get at the truth pull the drivers side head. All you need to know shall be revealed.

In any case a teardown will be necessary. I will assume your dealer will not be doing the repairs. Too bad you already signed on the new truck. You would have really had some leverage!

Good Luck.