2000 Grand Cherokee Cylinder 4 Misfire HELP

kbrown · 12-13-2011, 02:32 PM

First off this is my first post i believe i am in the correct section if not my apologies.

about a year ago i bought a 2000 grand cherokee 4.7 for a fair deal, or so i thought. knowing it had a "blown head gasket" i proceeded to purchase the vehicle. After pulling the heads off the passenger side head was done for, so instead of taking risk buying a new head and putting it back together i went ahead and ordered a new engine(assembled), 0 miles so i felt that it would be a smooth problem free vehicle engine wise for a while. well i was wrong. after getting the engine in it ran AMAZING i loved it and for what i paid i couldn't have been happier. a few days later i took the jeep on a road trip to see a show about two hours away all highway, constant 70mph not beating on it because it was new.
on my way back i had a check engine light come on, i was so close to home (5 minutes away) i just went on home scanned the code. it came up as a cylinder 4 misfire. i assumed coil pack and/or spark plug. replaced the coil pack and plugs, it was still there. so we started playing around with it. moving injectors and coils to see if the code would follow, nope stayed on cylinder 4. after brainstorming, we proceeded to test the connections to the coil and it was receiving power. now i have a jeep with a cylinder 4 misfire and rough idle. with no other vehicle my only option was to drive it. (i'm a student and i work no other options) i found this forum and I've been on here as a guest about 100 times looking for answers via search. i found it could be the crank position sensor or cam position sensor. replaced both with autozone parts. no go still a misfire on cylinder 4 and it was the ONLY code. after researching more and more i found jeeps like oem sensors. well off to the dealership it was, two new oem sensors and still a misfire. now the only conclusion i could come to was pcm. so online i ordered one brand new. hooked it all up and start it up, still a misfire! i take it for a ride and it was misfiring sooooo bad, way worse than the original misfire. bring it down reset it and it was back to a cylinder 4 misfire, did a compression test and it checked out perfect. I am at a total loss. and my MPG's are 13 on the highway!

current codes: cylinder 4 misfire and coil D not reaching maximum dwell time
P0304
P0354
randomly the check engine light will go off but it still has the rough idle.

the only modification is K&N cold air intake.

I'm going to assume the codes go hand in hand with each other.

the only possibilities i can come up with:
grounds (free) not leaning towards this though.
TPS
IAC
MAP
02
however if one was bad i would think it would have a code for the faulty sensor. knowing now that jeeps like oem parts, the cost to replace all of this is $$$ and being a student im not sure if i want to risk it and it still misfire.

anyone who can contribute information besides "search" thank you in advance!

kbrown · 12-13-2011, 02:40 PM

also no vacuum leaks.

nickblack · 12-13-2011, 02:46 PM

I don't have an answer for you, but I cant believe you threw all those parts at it without actually diagnosing the problem. You could have went to the dealer and had it diagnosed for 1/10th of what you threw at it. I am curious as to why you would keep throwing parts at something you had no clue as to what it was.

ufojeep · 12-13-2011, 02:59 PM

Have you done a compression check yet? My 4.0 was throwing a #3 and #4 cly misfire code. Did a compression check, it became obvious that there was a leak between the 2 cylinders. Didn't leak antifreeze, just compression. The head was fine, not warped, the Mopar kit was like $130 to fix, my mechanic charged me $200 to replace the head gasket. Now she runs perfectly. Just verify that you have good compression in every cylinder. BTW I drove mine a long time before fixing it, because I thought it would be very expensive to fix.

kbrown · 12-13-2011, 05:09 PM

It's $85 an hour, dealers are dealers and lets be honest after 10 hours or searching they still won't know what's wrong with it, well they will but they won't tell you. At least that's how it is here

kbrown · 12-13-2011, 05:10 PM

Quote:

Originally Posted by ufojeep

Have you done a compression check yet? My 4.0 was throwing a #3 and #4 cly misfire code. Did a compression check, it became obvious that there was a leak between the 2 cylinders. Didn't leak antifreeze, just compression. The head was fine, not warped, the Mopar kit was like $130 to fix, my mechanic charged me $200 to replace the head gasket. Now she runs perfectly. Just verify that you have good compression in every cylinder. BTW I drove mine a long time before fixing it, because I thought it would be very expensive to fix.

Compression checked out fine

kbrown · 12-13-2011, 06:54 PM

Bump

kbrown · 12-13-2011, 08:52 PM

Bump

seu83 · 12-13-2011, 09:00 PM

Pull the valve cover off and see if you can push the back(push rod side) of the rocker arms down on cyl 4. Sounds like it may be a collapsed lifter or a flat spot in the cam.

kbrown · 12-13-2011, 11:06 PM

I wil check that out when I have free time next and when it is not so cold. Thank you for your input. I sure hope it's not that otherwise I'll be a bit bitter pulling the motor in the cold to send it back to where I got it

kbrown · 12-14-2011, 06:23 AM

bump

kbrown · 12-14-2011, 04:21 PM

bump

Terminator2 · 12-15-2011, 09:14 AM

Move the coil pack wiring connector (not the coil itself) from the cylinder with the misfire to one of the cylinders next to it. If the misfire does not follow than I would pull the valve cover and check your valvetrain. Overheating can cause dropped valves but if yours did not overheat I would think valve spring broken maybe.

kbrown · 12-15-2011, 09:28 AM

Quote:

Originally Posted by Terminator2

Move the coil pack wiring connector (not the coil itself) from the cylinder with the misfire to one of the cylinders next to it. If the misfire does not follow than I would pull the valve cover and check your valvetrain. Overheating can cause dropped valves but if yours did not overheat I would think valve spring broken maybe.

thank you, looks like that valve cover is coming off pretty soon here seeing as school is done for the semester Friday. i will keep this updated with the things i have checked.

Terminator2 · 12-15-2011, 02:10 PM

Quote:

Originally Posted by kbrown

thank you, looks like that valve cover is coming off pretty soon here seeing as school is done for the semester Friday. i will keep this updated with the things i have checked.

That P0354 code is a coil 4 high impedance (resistance) code. Sounds like an open circuit (likely a bad ground) which will cause excessive resistance. If you already moved coil 4 to another cylinder and the misfire did not follow coil 4 to the other cylinder you should switch the wire connector that is going to cylinder 4 for one of the others and see if the misfire follows cylinder 4s coil connector. If so you have a wiring or connector issue.