Misfire Cylinder 4

T

TrueJeep565

New member
Hey guys I am having trouble with my 2008 jk. It has 120k miles on it and is throwing a PO304 code. Since figuring out the code I have replaced spark plug wires to all cylinders and replaced the spark plug to that cylinder (previous plugs had about 20k on them).

I'm thinking bad coil? But have noticed knock on startup (cold here in SD) which continues for about 5 minutes. Also just had manifold on drivers side replaced along with an injector cleaning service from dealership.

Any ideas? Thanks in advance.
 
WJCO

WJCO

Meme King
TrueJeep565 said:
Hey guys I am having trouble with my 2008 jk. It has 120k miles on it and is throwing a PO304 code. Since figuring out the code I have replaced spark plug wires to all cylinders and replaced the spark plug to that cylinder (previous plugs had about 20k on them).

I'm thinking bad coil? But have noticed knock on startup (cold here in SD) which continues for about 5 minutes. Also just had manifold on drivers side replaced along with an injector cleaning service from dealership.

Any ideas? Thanks in advance.
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Welcome back from 2013. You could always swap that coil to another cylinder and see if the misfire follows. A 5 minute knock doesn't sound good though.
 
2nd.gunman

2nd.gunman

Caught the Bug
TrueJeep565 said:
Hey guys I am having trouble with my 2008 jk. It has 120k miles on it and is throwing a PO304 code. Since figuring out the code I have replaced spark plug wires to all cylinders and replaced the spark plug to that cylinder (previous plugs had about 20k on them).

I'm thinking bad coil? But have noticed knock on startup (cold here in SD) which continues for about 5 minutes. Also just had manifold on drivers side replaced along with an injector cleaning service from dealership.

Any ideas? Thanks in advance.
Click to expand...

Wow almost 3 years to make your first post! Misfire only when cold is a bit strange are you sure it's not oil pressure, piston slap or timing chain rattle? I'm not real familiar with the 3.8 but what did the plug look like when you replaced it?
 
T

TrueJeep565

New member
Lol I know it's been a long time coming! I'm not familiar with piston slap... or any of the aforementioned things. But it doesn't sound good until it's warm. Hoping this is just a coil and the sound is a jeep thing but not entirely optimistic...
 
Blazindevl

Blazindevl

LOSER
Why would you only replace one spark plug when you're already going through the trouble? If you've approached your maintenance in the same fashion it could be any number of things! Anywho... Plugs, plug wires, coils, fuel injectors are all good things to look at. Have you replaced your fuel filter? Is your throttle body clean? Air filter? Doing a compression test and leak down test should rule out any internal issues with you motor. You're going to have to just start to narrow things down until you find your issue.
 
T

TrueJeep565

New member
In a crunch for time I decided to just do the one as I had previously replaced all 6 in the last 20k miles with oem plugs. I'm going to take it to the shop to have them check everything out, and will update. Thanks everyone for responses.
 
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