P0304 cyliner 4 misfire 2006 kj 3.7L

[cplchris]

As the title states: i have a recurring P0304 code for cylinder 4 misfire.

Long story short i have ruled out the following:

Vaccuum leaks
Pcv valve/leaks
Spark plugs
Ignition coils
Fuel Injectors
Throttle position sensor
Camshaft position sensor
Crankshaft position sensor

The misfire seems to be occuring primarily at idle when everything is up to temp and in closed loop mode but can sometimes be felt at low speed, low rpm with light throttle.

The long term fuel trim for bank 1 shows 5.5% and bank 2 (the side with the misfire) is at 10.9%

I have not yet performed a compression test or a fuel pressure test. I will probably be doing that tomorrow or i may just be taking it to the dealership to get it diagnosed.

Before i go and waste more money trying to solve the mystery, does anyone have any input?

Thanks in advance

 

[duderz7]

I've gotten misfire codes twice over the years. Cured both times with a can of berrymans fuel cleaner stuff. Mine was very minor though. Not noticable, just a code popped up.

 

[cplchris]

yea TBH i am thinking either valve seals or seats at this point. if it is seats i will probably just pull the head and have a local shop rebuild it.

 

[cplchris]

So after a compression test revealed no issues, i believe the problem is with the pcm or the wiring. Off to the dealership for diagnosis I go

 

[tjkj2002]

Sounds like a cat issue.

 

[cplchris]

My only reason for not suspecting the cats is that the problem is isolated to cylinder 4, if it were a clogged or otherwise bad cat wouldnt it affect the other cylinders?

 

[tjkj2002]

My only reason for not suspecting the cats is that the problem is isolated to cylinder 4, if it were a clogged or otherwise bad cat wouldnt it affect the other cylinders?

You see all sorts or weird stuff in my line of work,had a '07 KJ and a '05 WK with the 3.7's with P0304 caused by a bad cat.

 

[cplchris]

You see all sorts or weird stuff in my line of work,had a '07 KJ and a '05 WK with the 3.7's with P0304 caused by a bad cat.

never thought i would say this but, I will be relieved if I just need a new PCM.

thanks to dumb laws in NY a new set of CATs would set me back about 1250 plus the cost of new 02 sensors. CARB is ********.

 

[TomB985]

Can you clarify some of the steps you've used to rule out the above components? Did you physically swap them all to an adjacent cylinder and have the misfire stay on number 4?

I had a heck of a time with an intermittent misfire on my boat motor, and it turned out to be an internal failure of a spark plug that looked flawless to a visual inspection. Sometimes it's easy to miss something you don't expect.

 

[cplchris]

Can you clarify some of the steps you've used to rule out the above components? Did you physically swap them all to an adjacent cylinder and have the misfire stay on number 4?

I had a heck of a time with an intermittent misfire on my boat motor, and it turned out to be an internal failure of a spark plug that looked flawless to a visual inspection. Sometimes it's easy to miss something you don't expect.

swapped everything with brand new replacement parts. it was due for plugs and i figured at first it was a bad coil. when that didn't fix it I changed the pcv valve which was also due, checked the pcv lines and vaccuum lines, nothing out of the ordinary. then after a bit of reading and searching youtube, i figured it might be a faulty TPS, cam sensor, or crank sensor, replaced all 3 and still no difference then i figured, maybe it was a bad/clogged injector, ordered a full set of oem injectors, removed and purged the fuel rail, installed new injectors, tested resistance and listened to each one to be sure they were all being actuated, again no change. so fearing the worst, i finally did a compression test, and everything seems to be fine. so it is either a pcm issue, or as TJKJ said, a clogged cat. i never thought i would be hoping for a bad pcm, (cats are expensive and NY doesn't allow the sale or installation of anything other than carb approved OEM cats), a pcm is much less expensive.

in either case, it is at the dealership now for a diagnosis.

 

[TomB985]

Well, you through a lot of parts at it. That's good for ruling out the components themselves, but not wiring, which can also be an issue. How does it run, particularly under throttle? Does it ever feel sluggish?

The easy way to rule out the converter is to remove the oxygen sensors and taken for a drive. If the catalytic converter is clogged, releasing the pressure upstream will make the engine run better.

 

[cplchris]

dealership did a leak down test and the #4 cylinder was 15% faster than all the others.

looking at doing a new head on it this weekend or next weekend now.

 

[TomB985]

Well crap, that's no good.

Was it ever overheated? How many miles on it?

 

[cplchris]

155k on it, if it was ever overheated, it was before I owned it, bought it in 2009 with 48k on it. oil has been changed every 5k miles since I bought it with full synthetic and a nice filter, (mopar, napa gold, royal purple, or napa platinum filters, bg oil at the dealer and mobil 1 ep since i switched back to doing all my own maintenance) and BG MOA, and a can of CF5 in the tank, and then a separate tank with a fuel injector cleaner in it. I have always run good fuel, I have changed the radiator and coolant like 4 or 5 times, use hoat coolant, and a mopar cap and thermostat. and whenever I have had an issue, I address it immediately.

So after 9 years of owning it, i can honestly say i am not overly impressed with the vehicle. I will be replacing it with a chevy truck or toyota within the next year, something I wish I would have done rather than sink money into the jeep.

 

[Tin Man]

It's probably the valve guides, the 3.7L engine lasts only about 130-150k (if it's miles were talking about) before cylinder heads need to be done. Your 155k (miles) is actually pretty good. Just get them done and it'll run another 150 k nicely. Of course there's a ton of other issues you'll probably encounter (check the high mileage topic) but the motor shouldn't be one of them.

Just remember to get both cylinder heads serviced, the other one is no better and they both need the same amount of attention.

 

[cplchris]

It's probably the valve guides, the 3.7L engine lasts only about 130-150k (if it's miles were talking about) before cylinder heads need to be done. Your 155k (miles) is actually pretty good. Just get them done and it'll run another 150 k nicely. Of course there's a ton of other issues you'll probably encounter (check the high mileage topic) but the motor shouldn't be one of them.

Just remember to get both cylinder heads serviced, the other one is no better and they both need the same amount of attention.

i will do this one head and put maybe another 5-10k on the vehicle before i sell it or trade it in for something else. i'm tired of spending money maintaining a vehicle that i don't trust for a long distance trip.

 

[ltd02]

i will do this one head and put maybe another 5-10k on the vehicle before i sell it or trade it in for something else. i'm tired of spending money maintaining a vehicle that i don't trust for a long distance trip.

That's exactly why I got rid of my 02. I was just lucky to find the 05 when I did.

 

[Tin Man]

It's a wise decision. If you want reliable vehicle with 10+ years / 150k+ miles you should go for Chevy or Toyota. At the end of the day Jeep is a Chrysler and you can't do that with Chrysler. A friend of mine is a die-hard Chevy guy and when I tell him what I have done to my Jeep (-05) he always wonders "but isn't it almost brand new". (He owns -72 Corvette and -92 Astro).

 

[TomB985]

It's a wise decision. If you want reliable vehicle with 10+ years / 150k+ miles you should go for Chevy or Toyota. At the end of the day Jeep is a Chrysler and you can't do that with Chrysler. A friend of mine is a die-hard Chevy guy and when I tell him what I have done to my Jeep (-05) he always wonders "but isn't it almost brand new". (He owns -72 Corvette and -92 Astro).

Some brands are more reliable than others, but Chevy probably isn't one of them. I remember how much "fun" I had constantly working on a '95 Blazer and '03 TrailBlazer, and neither of which had 150K when they were dumped.

Maintenance matters quite a bit, but it comes down to luck of the draw for most things. The most reliable car I've ever owned was an '07 Kia Optima...that thing just didn't break, right up until the point I dumped it at 176K miles. Meanwhile a good friend of mine blew the engines in two Kias and swore she'd never go near another one.