Cylinder No. 4 Misfire

Ok, so that's the error code. Check engine light flashes when accelerating and engine stutters like Porky Pig. There's also a distinct "pop!" sound, right about every 5 seconds or so.

I pulled the plug and it appears to be carbon fouled (black, smells more like gas than oil). Other plugs were wearing normally, but they got replaced anyway as it was waaay past time for a spark plug change. After replacing the plug, the problem with all the above symptoms is still there.

Any suggestions?

EDIT: Oh, I suppose it might also be helpful if I mentioned that it's an '05, 3.7L.

I'm gonna take a random stab at it and say check the injector..

Yeah, that's my next step. Thought I'd post my question though in the meantime, thinking that maybe some of the posters one here might be more car savvy than I. (Haven't had to do much work on car in a while, and last time I did was about 10 years ago and it wasn't fuel injected nor computerized.)

Shall I check the flux capacitor and blinker fluid while I'm at it?

Ok but seriously, can I assume that the carbon-fouling is most likely from a clogged injector? I do my own brakes and small stuff like that, but this whole misfire thing has got me rattled a bit. Please no low compression, please no low compression, please o please o please...

MickityMike said:

Shall I check the flux capacitor and blinker fluid while I'm at it? ...

Click to expand...

don't forget your exhaust bearings!

If it was me I would switch that #4 coil pak with the #1 and see if the code moves. (I take it you have a P0304 misfire code and no others) Then if the misfire moves to #1 the coil pak is bad. You could try that first and see what happens. Make sure the coil pak wireing connector is securely snapped in place. You might have to put another plug in #4 if it got all fouled because of the misfire.

Just some thoughts.

Dave

with that pop, I highly doubt it's your fuel injector, ignition coil, or spark plug... I'm banking on something to do with the valve train...

How many miles are on it?

Could be broken valve spring, sticking valves, bad lifter... couple of things... but i'm pretty sure it's your valve train

ShadowedXistence said:

with that pop, I highly doubt it's your fuel injector, ignition coil, or spark plug... I'm banking on something to do with the valve train...

How many miles are on it?

Could be broken valve spring, sticking valves, bad lifter... couple of things... but i'm pretty sure it's your valve train

Click to expand...

Well, crap.

It's at 80,*** miles.

Damn, I was afraid it was going to be something with the valve train... That popping sound makes me nervous.

I am at 90xxx and I just had to pull the valve cover off, turned out it was a bad lifter... $16 part... but of course you need a special valve spring compressor to get the rocker arm out to get to the lifter... the tool is around 65 new... I picked one up for 30 off ebay... hope this helps... of course check everything else first... lol... it really wasn't all that difficult to do, but just as other members told me, there are a lot of variables and such around there, that you really have to be careful of... they recommend having a professional do it... still not a bad idea... but if I had to choose to do it myself again or take it to a shop... I'd still do it myself...

Yeah, I don't know how comfortable I'd be doing that. The pucker factor in that kinda stuff is really up there, but then again, I'm guessing the labor for a pro to do it is up there, too. Jaysus.

Any idea how much that'd run me to have done? A million dollars?

no not quite that much... You'll have to have the coolant refilled (since they have to pull your coolant lines off your heater core to remove the valve cover... might as well flush the radiator if your jeep has never had it done (especially if you already have to put new coolant in it)... might as well change the oil in the same process... they should already have the tools to compress the valve spring... Probably looking at I would say between 4 and 500, but that's without any replacement parts (as there are a lot of parts to your valve train, and who knows what could be causing the problem)... if they have to remove the head to service the entire head, you are probably looking at over 1000...

and just to clarify things... THIS IS ONLY IF IT DOES TURN OUT TO BE YOUR VALVE TRAIN!!!!!

It very easily could be something else... I'm just saying my GUESS.. is the valve train... good luck!

Hmmm, I was thinking about this last night. If it were something with the valve train, wouldn't it seem reasonable that the "popping" sound would occur a lot more than just once every 5 seconds? That seems like a pretty odd interval to be something with the VT, ya know?

Does the popping increase with rpms? And the answer to your question, is not really... There are two cycles per cylinder. One for intake and one for exhaust...

Yeah, ignore that last post.

So, after going through the punch list, there's only one thing left: valve train. What a bite in the ass. Though I suppose this is what I get for buying a used car... Expletive.

Oh well. I'm laid off right now (I hear the economy's kinda crappy?) so I've got time on my hands. Maybe I'll post pics of the upcoming operation.

you plan on doing it yourself or taking it to a shop?

Well, like you said in your other thread, if I do it myself and **** it all up only thing I've wasted is my time, so... why the hell not? I've got a friend who's done this before and he's offered his help, so yeah, I'm going to do it myself.

Way I look at it is I've got no job (laid off civil engineer) so I've got the time!

I'll be posting pictures of the operation and of my nervous shakes.

That's good you found my thread on it, let me know if you have any questions... And make sure you get yourself the valve spring compressor tool you will need. Ill get the part number on that tool for you.

A couple of years back our KJ had the same thing.
"Cylinder No. 4 Misfire"
Turns out all that was needed was a new set of spark plugs!

ShadowedXistence said:

That's good you found my thread on it, let me know if you have any questions... And make sure you get yourself the valve spring compressor tool you will need. Ill get the part number on that tool for you.

Click to expand...

Already got it, but thanks! I think AutoZone will loan that out, too, so I won't have to buy it. My buddy is (allegedly) coming by tomorrow or the next day so we can do a compression test. I'm having this reoccurring nightmare that it's a cracked head. It'd be pretty nice if it's only a bad spring or something rather than a failed gasket or cracked head. That'd suck. A lot.

Though you'd think if the gasket or head were bad, it'd be more than just one plug that's fouled.

At idle, the engine RPMs are, say even 600 average. That popping noise happening once every 5 seconds? Well, the crank has already rotated about 5 times at 600RPM for five seconds. If it were a popping noise due to an open or partially valve on the compression stroke, it would happen about every 2 seconds at 600RPMs? Something like that, I would alto think that 5 seconds is too long an interval, isn't it?

That was kinda where I was going with that earlier post, PS, but then it decided to start increasing the noise with RPMs. I'll know more after the compression test (or maybe I won't). We'll see.