View Full Version : baffling cylinder misfire

11-21-2014, 10:53 AM
I have a 2002 Jeep Liberty, 3 months ago Jeep would start shaking with the service engine light flashing. When ignition was shut off and restarted Jeep would drive fine, code was for a cylinder misfire.Since the coil packs was factory decided that was the problem, replaced coil packs and plugs. No problems for a month then same thing would happen, Jeep would start shaking with the service engine light flashing. When ignition was shut off and restarted Jeep would drive fine.Replaced the cam and crank sensors, this also worked for a while and then out of the blue Jeep would start shaking with the service engine light flashing. When ignition was shut off and restarted Jeep would drive fine but this time noticed that when Jeep would start shaking would take foot off accelerator and the Jeep would smooth out and drive fine.BTW we have had the Jeep for 10 yrs, purchased used with 40,000 miles on it currently have 400,000 miles on it. Would like to get more miles before breaking down getting a new one.

11-21-2014, 10:56 AM
Do a compression test on all cylinders.

11-21-2014, 11:44 AM
I wonder if you might have a bad fuel pump. Our Chrysler minivan misfired when the engine was under load, but ran smoothly under light throttle. A local shop diagnosed it as a failing fuel pump, which couldn't supply enough fuel to run the engine if the throttle was wide open. The shop replaced the pump, and everything was hunky-dory (until a week later, when a hose they'd failed to tighten properly popped off, spraying fuel all over the road and stranding us--but they fixed that without a fuss).

11-21-2014, 03:57 PM
I strongly suspect/suggest fuel filter. Fuel flowing thru it gets it glogged just enough for the engine to run roughly. Stopping the engine or letting up on the throttle stops or reduces the flow of gas enough to un-clog a bit...

P.S. "Jeep" is a company.

california jobcase
11-21-2014, 04:37 PM
Jeep may be a company, but so are Ford and Chevrolet, and lots of people refer to their cars as Fords, Chevys, Toyotas, etc. Nothing wrong with calling a Jeep a Jeep, the way I see it.

11-21-2014, 07:05 PM
What OBDII codes was it showing? That's a place to start troubleshooting.

11-21-2014, 07:19 PM
What OBDII codes was it showing? That's a place to start troubleshooting.

Exactly, need this before guessing can start.

11-21-2014, 09:25 PM
Have you tried pulling the plugs to see what they look like? I don't know if 3 months is enough time for the plugs to show some obvious symptoms but they might give you a clue as to what is going on.

This chart might come in handy.

I also recommend changing the fuel filter. I've had a lot more problems in recent years with clogged fuel filters than I ever had in the past. I don't know if it's current production methods or just older tanks in the ground rotting and having debris in them or what.

A catalytic converter can cause problems too, especially if the honeycomb inside rots and comes apart. If it happens to blow up against the back of the cat and stop up the air flow, the back pressure will cause you all kinds of problems. Stop the engine, and all of the broken pieces in the cat fall to the bottom and you're fine until they just happen to blow around and stop up the air flow again. An engine that is running lean will often burn out the cat so a fuel mixture problem could be the ultimate culprit.

EGR problems also tend to show up when the engine is warm and disappear if you stop and let the engine cool down. I'm not sure how well it really fits your symptoms but I thought I would mention it even if it isn't the most likely cause of your problems.

Getting the actual engine codes might help narrow it down but hopefully that at least gives you some other ideas to consider.

11-22-2014, 06:59 AM
Changing the fuel filter would be in the category of "cheap enough to be worth a try" if you're doing your own work (especially if it hasn't been done in a while), but it shouldn't be too hard for a shop to just check the fuel pressure to see if that's an issue.

Other than that, man, 400,000 is a lot of miles and this era of Chrysler product isn't exactly known for longevity. I'd agree with doing a compression test or at least checking the plugs before you go too crazy trying to diagnose the thing. Even if it doesn't uncover the problem, it might give you an idea of how much more money you want to pour into the thing!

The thing that's sort of baffling is that changing the plugs and coils apparently fixed it up for a month, right? The only thing I can really think of short of a bad part (which wouldn't be unheard of) is that you've got a cylinder with bad rings or a bad valve that's fouling the plug and so a new one fixed it for a while. I'd have assumed a mechanic would have noticed, but maybe they figured the plugs being trashed would be normal with that much mileage. Also, does the car burn any noticeable amount of oil or ever smoke at all?

11-22-2014, 07:44 AM
GJ they all ready have thrown a ton of $ at it, so what's a fuel filter?
I can see it being a pressure/ volume issue at high load.
A pressure test sitting still might not reveal it. Driving the car with a gauge attached would.
Also we don't know if it is the same cylinder misfiring each time or it truly random.
The same cylinder might point to a mechanical issue. Totally random does not, at least in my mind.

Dallas Jones
11-22-2014, 11:26 AM
Do you have a code reader of your own and read the codes yourself, what were they? The cylinder misfire codes may point to a particular cylinder.

My second question is did you read the codes after the coil packs were replaced and if so, did the misfire move to a different cylinder?

The symptom of a cylinder misfire, which what is causing the shaking, and that the shaking eases up when not under a load to me indicates that their may still be a bad coil or connection. I would re-check the coil work, plug connections, before going further.

11-22-2014, 12:03 PM
If it seemed to clear up after being worked on it sometimes indicates a corroded connection that will temporarily be repaired just by removing and replacing. I would carefully inspect all related connections.

Gary T
11-22-2014, 12:33 PM
A faulty throttle position sensor (TPS) can cause misfires on Jeeps. This would be consistent with the symptom changing when lifting off the accelerator. TPS glitch usually will not show up on tests (lab scope, multimeter, etc.). Just replace TPS.

11-22-2014, 05:29 PM
Surprise that it has not happened in 3 days,running perfect.I have not changed gas stations or grade of gas used in it. The Jeep Liberty does not smoke or use oil, plugs looks light grey but with no oil residue on them. Thanks for all the responses , next time this happen fuel filter will be next thing to do.

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