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Old 07-26-2011, 03:45 PM
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2001 G. Cherokee 4.7 misfires

Hi guys.

First of all, my technical english is a bit rusty but I will try the best I can.

I have an 2001 GC 4.7, which feels like running on 7 cyl. There are no permanent fault codes and the car has new sparkplugs. All coils has been checked and working ok.
Still: When I disconnect the wirings on the coil for cyl. 3 there is no difference in engine idling/smooth-running. Plug/coil new and checked.
There is no difference if I unplug the injector on cyl. 3 either.
Doing this immediately lights up engine-lamp, no immediate faultcodes without disconnecting wires.
There is also a clicking/rattling noise similar to vavle-lifter failure( I`m guessing this is brought on by failure mentioned above)
Cylinderhead-cover has been taken off for inspection, couldnt see anything wrong. Everything was where it should be, no broken valvessprings. and all the valves opens.

Does anybody have some hints for me? I`m tired of my car not running properly and using extremely much gas.

Jostein - Norway
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Old 07-26-2011, 04:15 PM
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Re: 2001 G. Cherokee 4.7 misfires

may have a bad valve, you may want to do a compression test
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Old 07-26-2011, 04:17 PM
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Re: 2001 G. Cherokee 4.7 misfires

If you can disconnect the COP and injector from cylinder 3 and it keeps the same miss, it's pretty safe to say that #3 is causing the problem.

If you have new plugs and coils that have been checked, then you should be good on the "spark" area. The next obvious thing is the fuel delivery through the injector. Have you checked to make sure it's good? You can swap it with another cylinder and see if the miss fire moves w/ the injector.

If it's not the injector then I would do a compression test and a leak down test.
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Old 07-27-2011, 02:33 AM
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Re: 2001 G. Cherokee 4.7 misfires

you need new lifters and a new rocker.

pull the valve cover off and I would bet you will find a rocker has dropped off and is laying in the head. Very common on the wj 4.7 (at least in my area), and it may be common on the wk just not enough miles on them yet. When the lifter doesnt pump up the pressure keeping the rocker in place is relieved and it falls off.

That said, a rocker can also fall off if you were to have dropped a valve seat and it was preventing the valve from coming all the way back, again, same reason, tension is relieved from the rocker and it falls out. A leakdown test would help deturmin cylinder integrity. Ultimately you could just snap the rocker back in, start it up and see how it runs. IF it fell out it fell out for a reason so dont expect it to continue running perfectly forever just snapping it back in.

Also if your driving it like this I HIGHLY suggest you disconnect the #3 injector. Driving on a dead cylinder is straining on an engine, but dumping gas into the cylinder that is not producing then shoving it out into the exhaust (or dependant on what valve is not opening just pooling it up and pushing it into the crankcase)... raw fuel in the cats is bad mmkay! (sorry easier to translate english... unburned fuel in the catalytic converters will melt them down VERY quickly).
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Old 07-27-2011, 07:08 AM
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Re: 2001 G. Cherokee 4.7 misfires

Quote:
Originally Posted by onkeljoma View Post
Cylinderhead-cover has been taken off for inspection, couldnt see anything wrong. Everything was where it should be, no broken valvessprings. and all the valves opens.
Quote:
Originally Posted by 2005JGC View Post
you need new lifters and a new rocker.

pull the valve cover off and I would bet you will find a rocker has dropped off and is laying in the head. Very common on the wj 4.7 (at least in my area), and it may be common on the wk just not enough miles on them yet. When the lifter doesnt pump up the pressure keeping the rocker in place is relieved and it falls off.
Based on the statement in the OP, it sounds like he has already removed the valve cover (I can't think of anything else that would be called a "cylinerhead-cover") and everything looked fine. Hopefully he would notice if a rocker dropped off.
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Old 07-27-2011, 10:27 PM
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Re: 2001 G. Cherokee 4.7 misfires

The engine is running rough and most probably misfiring, but you dont get any misfire code(s)? As Jeepme mentioned, i would also start swapping the #3 injector with an other cylinder and see if this will make any change.
Did this problem suddenly start, or was any maintenance done? The noise you are hearing, do you have a mechanics stetoscope to find the place where its more clear to hear? It still could be a not properly working lifter, causing the noise and a much shorter valve opening time. There could still be combustion, but with not enough oxygen (when problem is the intake valve) or too short exhaust valve opening. Did you see any different colour of the #3 ignitor?
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Old 07-28-2011, 01:30 AM
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Re: 2001 G. Cherokee 4.7 misfires

Quote:
Originally Posted by JeepMe View Post
Based on the statement in the OP, it sounds like he has already removed the valve cover (I can't think of anything else that would be called a "cylinerhead-cover") and everything looked fine. Hopefully he would notice if a rocker dropped off.

at least some of us read... I just got to a what sounded like a dead miss, and rattling noise and made a suggestion. Good call though, he has already done it.

It may be a dropped valve seat, a leakdown test to confirm would be good.
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Old 07-30-2011, 05:44 AM
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Re: 2001 G. Cherokee 4.7 misfires

Cyl. head cover= valve cover. As I said in the first post..my tech. english is a bit rusty.

The reason for the "misfire" was a clogged up injector, still rattling from a lifter tho, but runs on all 8!
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Old 07-30-2011, 01:50 PM
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Re: 2001 G. Cherokee 4.7 misfires

Yikes now thats a plugged in injector! I would reccomend running some seafoam or other injector cleaner through the next tank or 2 of gas to clean up the others just in case. Maybe half a can of seafoam in the oil a few hundred miles before your next oil change would help free up the lifter too.
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