Threw a code - P0304

Joe Jeep Owner · **Posted:** Tue Apr 15, 2008 9:52 am

Cylinder misfire detected, cylinder 4

Listed the following possible causes:
Ignition system fault - spak plugs, ignition wires, coil
Vacuum leak
Injector fault
high or low fuel pressure

Check engine light came on and it seems to be stuttering more and more.

Checked the air filter to see if it was clean and dry (good/repalced/checked seal was tight)
Checked the spark plugs and they look like they could be replaced
Coils look good as far as I can see

Bringing it in to have someone recheck the plugs/coils and replace (I'm at $64K anyway) but my buddy who normally does the work is out of town for a few weeks so I'm going to a mechanic that was referred to me. Just want to make sure I have everything covered incase he winds up being less than honest with me.

Spark plugs/coils or cleaning the injectors should solve my problem I'm hoping but is there anyting else that I should check into or it could be?

DryBones · **Posted:** Tue Apr 15, 2008 10:14 am

if you can check the plugs then you can replace them. I would start there. only took me an hour on my first try.

Jeep4me99 · **Posted:** Tue Apr 15, 2008 10:43 am

pull the coil pack from cylinder #1 and put it in #4 and vice versa. If cylinder #1 starts misfiring then it is a bad coil pack.

tommudd · **Posted:** Tue Apr 15, 2008 4:03 pm

check the plugs on the coil packs as well, have seen a couple of times if you just unplug them and plug them back in they are OK. Switching coil packs will help in identifying if a coil pack is the problem. Just go all over the engine and look for wires, vac. lines off or something easy 5 minute look see. Most times it is something simple

You have replaced the spark plugs before not original right? I hope?!! If so how many miles on the plugs?

Joe Jeep Owner · **Posted:** Tue Apr 15, 2008 4:10 pm

Thanks, I will try that tonight and see how it looks. Does the check engine light go off if the problem is fixed or does it have to be reset?

Normally I would do something like this on my own but I just dont have the time lately, coming in early, working late, rennovating the house, oh and a baby due in 2 months! LOL At this point it is just easier to drop it off and pick it up.

tommudd · **Posted:** Tue Apr 15, 2008 4:14 pm

Should reset in a couple of starts if it fixes the problem
Good Luck sounds like you have your hands full there!

Joe Jeep Owner · **Posted:** Thu Apr 17, 2008 10:00 am

Just got the call from the shop, need plugs and coils. They also asked if the check engine light flashed or stayed solid when it first came on, if it flashed that means possible damage may have been done to the catalytic converter and that may have to be checked/replaced down the road (they dont have anything to check it now) :roll:

He said the check engine light could come back on anywhere from an hour later to a couple of days later and that could be the cause.

Does this sound right? I think it might have flashed but I cant remember at this point. I have been driving the Jeep short distances since Sunday (when the problem started) and it has been fine other that the occasional sputter (slight loss of power).

Like I said, this is a friend of the guy who usually works on my Jeep and I dont think he would screw me. Then again, I dont trust too many mechanics and would rather confirm it with the pro's here for my own piece of mind.

DryBones · **Posted:** Thu Apr 17, 2008 11:59 am

no way all 6 coils have gone bad at the same time. plugs probably need replacing and maybe the coil on cylinder #4. I would just start with the plugs and see how it goes after that.

tommudd · **Posted:** Thu Apr 17, 2008 12:05 pm

I would do the plugs as well and have them replace that one coil pack if needed but not all.

If you would of ran it a long distance then maybe the cat may need replaced but not just the short trips you have done.

Jeep4me99 · **Posted:** Thu Apr 17, 2008 12:10 pm

Joe Jeep Owner wrote:

Just got the call from the shop, need plugs and coils. They also asked if the check engine light flashed or stayed solid when it first came on, if it flashed that means possible damage may have been done to the catalytic converter and that may have to be checked/replaced down the road (they dont have anything to check it now) :roll:

He said the check engine light could come back on anywhere from an hour later to a couple of days later and that could be the cause.

Does this sound right? I think it might have flashed but I cant remember at this point. I have been driving the Jeep short distances since Sunday (when the problem started) and it has been fine other that the occasional sputter (slight loss of power).

Like I said, this is a friend of the guy who usually works on my Jeep and I dont think he would screw me. Then again, I dont trust too many mechanics and would rather confirm it with the pro's here for my own piece of mind.

Joe, before you get ripped off...
1. Autozone can check your packs. take the jeep there, pop the hood and bring them in.
2. change the spark plugs yourself, why pay someone 65 bucks just to change them when you can do it with almost 0 knowledge
3. Catalytic converters have a a super long warranty mandated by the EPA. The CAA requires an 8-year or 80,000 mile warranty on the major emissions control components such as the catalytic converter. Do an internet search, DO NOT LET THE DEALERSHIP CHARGE YOU FOR A NEW CAT.

nobster · **Joined:** Wed Mar 12, 2008 2:52 am **Posts:** 126

hi all, i threw codes p0300 302 303 304 a couple of weeks ago, took it to jeep the next day and they could'nt find anything wrong with it, reset the codes and it's good as new. i'll be changing the plugs next service at the end of the month though.

Sean · **Posted:** Sun May 11, 2008 3:50 pm

At 32K I had a similar experience, dealer said no compression in cylinder 4. They replaced the Powertrain Control Module (PCM) and that fixed the issue.

Good luck,
Sean

Joe Jeep Owner wrote:

Cylinder misfire detected, cylinder 4

Listed the following possible causes:
Ignition system fault - spak plugs, ignition wires, coil
Vacuum leak
Injector fault
high or low fuel pressure

Check engine light came on and it seems to be stuttering more and more.

Checked the air filter to see if it was clean and dry (good/repalced/checked seal was tight)
Checked the spark plugs and they look like they could be replaced
Coils look good as far as I can see

Bringing it in to have someone recheck the plugs/coils and replace (I'm at $64K anyway) but my buddy who normally does the work is out of town for a few weeks so I'm going to a mechanic that was referred to me. Just want to make sure I have everything covered incase he winds up being less than honest with me.

Spark plugs/coils or cleaning the injectors should solve my problem I'm hoping but is there anyting else that I should check into or it could be?

Jeepjeepster · **Posted:** Sun May 11, 2008 6:53 pm

Sean wrote:

At 32K I had a similar experience, dealer said no compression in cylinder 4. They replaced the Powertrain Control Module (PCM) and that fixed the issue.

Good luck,
Sean

Maybe Im missing something but how does a PCM have anything to do with compression in a cylinder?

Neatus · **Posted:** Tue May 13, 2008 1:25 am

This thread helped me solve my misfire problem...thanks!

tommudd · **Posted:** Tue May 13, 2008 1:31 am

Neatus wrote:

This thread helped me solve my misfire problem...thanks!

so what was the problem you found ??

Edvalencia · **Posted:** Tue May 13, 2008 11:52 am

Something really strange that I found.....

For months, I had been getting a Misfire in Cyl 6 code. It would only do it when the engine was cold, but it did it every day. The engine would shake & the check engine light would start flashing. As soon as I shut the engine down & re started it, it would run fine. I tried new plugs & packs, but it did not help.
As I was reading through the forum, I happened on a thread about coolant. I had put some generic coolant, which according to the thread was bad for the Jeep. I decided to do a coolant change and put the correct type of coolant (the name escapes my brain - no coffee). Long story short, as soon as I flushed and replaced the coolant, the Misfire code disappeared. That was several months ago, and so far so good. Another thing I noticed was that my coolant kept getting low. That is no longer happening. I'm sure there was some cause & effect going on there. (Too bad it didn't fix my non functioning power seats)

Threw a code - P0304

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