engine knock/misfire

[theholybull]

Ive got a problem with my 02 libby with the 3.7. I took off to take my kid to school today and there was a sudden arrival of engine knock and an immense loss of power. I was less than a mile from the house so i nursed her home. I figured the worst, blown head gasket. i checked the oil, no coolant on the oil. I checked the plugs, no coolant. I checked compression, all clyinders over 100. Switched coil packs around still runs rough. All my plugs are a little sooty except for the number 6 plug. I sprayed carb cleaner around the intake and there are no leaks. It sounds like there is something banging around in the intake, almost like the engine is back firing through the intake. I wont have a scanner to pull the codes untill later tonight so right now im at a loss. The only thing i can think of is that i lost a crank or cam sensor and its defaulted to bank injection instead of multi port, i know this happens in chevys and fords but im not sure about jeeps. Ive pretty much ruled out valve issues and a blown head gasket due to the compression tests and lack of coolant any where but in the cooling system It almost has to be a sensor, can anyone tell me whats going on here?

edit: the mechanical timing is dead on as well, so it didnt jump time and that rules out another issue.

 

[kj924]

Will it rev past 2k? Does it sound like hitting a rev limiter at that point?
Mine gave me some troubles last week in the freeze/melt weather we had. Mine was crank position sensor. A "knock" sounds a bit more serious than what I had though.

 

[theholybull]

Yea she revs ok. I just noticed a lot of sludge in my oil filler neck, I dont think that its an oiling issue however. Its not coming from a head ive gon over them with my stethascope and its coming out of the intake. God i miss points and distributor caps.

 

[tjkj2002]

You should have well over 175psi for compression in the 3.7,if not you got some issues.Probably need to pull the valve covers and check for a popped off rocker/follower or a dropped valve.


Oh and the 3.7 will always fire the injectors one at a time,never a whole bank at once due to the 6 separate injector drivers in the PCM,same goes for the coils also as there is 6 separate drivers for those as well.

 

[theholybull]

I found the problem, the rocker popped off on cyl 4 exhaust valve, it was causing the pop i heard in my intake. the lifter froze up and that was the reason i dropped the rocker. i replaced the lifter ($8 part thats made in the u.s.). If it happens again ill replace all the lifters and valve springs. The reason i had the popping was the gasses in the cyl had no where to go due to the fact the exhaust valve wasnt opening and when the intake opened the gasses were flowing back into the intake causing the pop/knock. just keep that in mind in case you have the issues i had, im just glad i didnt wipe the engine. I was also worried because i had the yellow sludge in my filler neck but upon inspecting the heads they were clean as hell, and on top of that my cam journals looked great for 101k.

I just wanna thank all of you for the great info on the boards for giving me an idea where to start looking, if not for that id have started replacing sensors willy-nilly and i would still be searching for the problem instead of sitting here on my couch drinking a nice cold beer.

thanks and hope this helps someone else
Bull.


P.s .The compression tester we had was an olod napa tester that has a rubber tip that you hold on the head, due to the location of the spark plug holes its hard to hold the tester on above 100 psi, knowing that i assumed the compression was good.

 

[ridenby]

Glad you found problem and got it fixed.

 

[LibertyTC]

Another 100,000 mile mark lifter problem.
Glad theholybull you got the problem solved.
What is it lately with loosing rockers after 100k..
Maybe it is time to consider replacing the springs, lifters and rockers in advance of further problems once you get those miles on.
I did notice it was an 02, I think some changes took place in the head in 03-04 wonder what they were..

 

[theholybull]

Thats what i get for buying one as soon as they came out. I was smart on the KK, I waited until 09 to buy one, Let them work the bugs out in the first year. There was an upside to buying the 02 as soon as they came out, I didnt get a prelowered libby. I was running 255 70s from the time i got it until the time i lifted it. Im just glad the lifter tick ive heard for the past year is gone. That lifter was frozen up and undoubtedly the culprit. Like i said before when it happened i swore to god i had lost a head gasket. Im
SO glad it was that lifter.

 

[kb0nly]

Good to hear you got her fixed up!

PS: Oil cap sludge is a very common thing on the KJ due to the large filler neck/funnel they have, allows moisture to condense up in there and build on the cap. Mine usually gets a little of it, not a lot, just enough on the bottom of the cap to annoy me. It's gotten a lot less after a few oil changes, i don't know what it had for oil when i bought it but i use Castrol GTX, and after a few changes the sludge went from yellow goo on the cap to just a few drops of sludge from moisture, so the type of oil you run does seem to make a big difference.