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Old 08-13-2015, 11:32 AM
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Cylinder 6 Misfire Help

I bought my 2004 Jeep Liberty towards the end of June this year. Upon purchase, the check engine light was on but the dealership said they would resolve that issue before I drove it off the lot. The CEL was off when I picked the car up but after driving at highway speeds, the light came back on and started flashing. I took my jeep to Midas to have it looked at where they replaced two coils packs and all six spark plugs. The light was off when I picked it up but sure enough the next day it was back on.
Midas looked at it again and found that something wasn't connected all the way so they fixed that. My jeep drove fine for about 2 weeks before I drove on the highway again. The light came back on and would flash every once in a while. So I once again took it to Midas ( a different one this time) and they spent 3 hours looking under the hood. They concluded that they have no idea what the problem could be.
I then had to drive my jeep on the highway again with the CEL on. After the car sat around for 6 hours, the light came off so I drove on the highway without the light on the second time. Sure enough though the next day when I turned the car back on, the CEL is on all the time and flashes about 85% of the time when driven.

Has anyone else had this issue? Is there any solution?

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Old 08-13-2015, 12:26 PM
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Re: Cylinder 6 Misfire Help

Welcome to the garage.
You donīt have any warrantee from the place you bought the jeep?
What is (are) the fault code(s) stored by the PCM? The title says cylinder 6 misfire, but it would be nice to have the actual fault code(s).
You should be able to check the fault codes yourself by doing the keydance; ignition switch off/run three times and leave in run at the third time. The odometer will show "DONE" when no faults stored, or each fault at a time.
Does the engine run rough when the check engine light comes on?
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Old 08-13-2015, 12:33 PM
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Re: Cylinder 6 Misfire Help

The warranty cost half the price of the car so at the time it wasn't worth it.

I just rechecked the codes and they are: P 0300, P 0301, and P 0306.

It definitely drives a little rough when the light is flashing. It drives okay when the light it just on but it's probably not exactly how it's supposed to feel. It feels like the car is almost bouncing when the light is flashing (if that makes sense.
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Old 08-13-2015, 12:54 PM
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Re: Cylinder 6 Misfire Help

Ok, P0300 is a random misfire code, the P0301 and P0306 respective cylinder #1 and #6 misfire.
Misfires can be caused by several things and i presume that the coils changed where for cylinders 1 and 6?
That the misfire only happens on the highway, makes me think that it could have to do with sticking exhaust valves. (a valve which is sticking due to carbon buildup on the valve stem, will normally show up at higher rpm. The carbon makes the valves closing operation slower, so at higher rpm it can still be slightly open and reduce significantly the pressure in the cylinder during compression, causing a misfire)
I would try a seafoam treatment through the brake booster line. Seafoam is a strong de-carbonisation product. You will have to let half of the bottle be sucked slowly through the brake booster line on an idling engine, without letting it stall. As soon as half of the bottle is sucked in, shut down the engine and let it soak for an hour or so. Then take it for a ride on the highway, to clean it up well. Be prepared to see lots of white smoke coming from the exhaust, from the moment you feed the seafoam through the brake booster line until quite some time after starting to drive. It can be necessary to repeat this procedure a second time.
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