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Unread 06-21-2013, 11:07 AM   #1
johnfair@izoom
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P0301 code

The code stats Misfire Cylinder #1.

The Jeep, 4.0, '04, runs fine. If I get on the gas, like from a stop light. After a couple minutes when I am idling again, it idles rough and then the check engine light comes on. After a couple days of this, it goes away and everything is back to normal idle. Thought maybe it was a bad spark plug so replaced those, still same problem.

thoughts?

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Unread 06-21-2013, 01:48 PM   #2
Jeepster83
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P0301 - Cylinder #1 misfire detected

If you changed your spark plugs and the problem still exists then I'd look at the cylinder #1 injector. pull it out and see if its dirty.

Injectors are sort of like spark plugs when it comes to replacing them. Sure you can do just one and get away with it, but if one fails then it's a fairly safe bet the others aren't far behind. Also, before condemning an injector, look at the wiring going to the injector. Injectors are switched on and off via the ground side and if you have a bare wire against the intake or head or block then you have a dead short before the injector. That would cause an intermittent P0301 as well.
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Unread 06-21-2013, 01:50 PM   #3
johnfair@izoom
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But would it also be something that will clear it self up after a couple days. The check engine light will go back off, and the engine will idle fine until get on it again.
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Unread 06-21-2013, 02:32 PM   #4
SlackJaw
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I get 420 a lot, and many times 301 is included. I had been thinking that 420 was due to loose exhaust flange, but i understand that shouldn't cause a miss.

The miss usually comes after long periods of granny driving, so I always assumed it was carbon build up on non-rotating valves. If I get on it through 1st and 2nd, over 4k rpm (rotating the valves), the idle is then smooth.

But now you got me wondering about my #1 injector, as this too could cause 420 cat error.

Anyway, mine is similar in that it comes and goes...I'm not terribly worried about it, but yeh, would be nice to solve.
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Unread 06-21-2013, 04:43 PM   #5
Jeepster83
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Quote:
Originally Posted by johnfair@izoom View Post
But would it also be something that will clear it self up after a couple days. The check engine light will go back off, and the engine will idle fine until get on it again.
A misfire will cause the MIL to come on, and then several key cycles/drive cycles without the misfire will turn the MIL off. The injector harness is partially encased in a plastic shroud. If you don't see any exposed/frayed/broken wiring there then a small flathead screwdriver will open it up so you can inspect inside. Carefully follow the wires from each injector as far as you can (don't pull out ALL the wires, keep it neat so it's easy to put back together) and check for exposed wires or melted wiring insulation or anything you think would cause a short.

It may not be a shorted wire. Locating shorts can sometimes be tricky but other times they'll jump right out at you. A careful inspection is always where you start.

Cleaning out the valves like SlackJaw mentioned is another simple thing and should be done regularly on lightly driven vehicles. Your symptoms sound like a bad/shorted injector though. Have you used any fuel system/injector cleaner recently?

EDIT: a shorted injector will flood the cylinder. Pull out #1 plug again and smell it. If it smells strongly of gasoline then I'd be looking at finding the short.
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Unread 06-21-2013, 05:08 PM   #6
Jaminjer
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I kept getting 306, same code but cylinder #6, changed plugs, still same error, changed TPS still same code, changed coil pack havent had code since.
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