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Old 01-13-2014, 01:22 AM   #1
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Code P0301 and poor startup. PLEASE HELP!

Hello all,

I bought my manual '04 wrangler about 6 months ago. It has 70k miles on it. Since buying it, the startup has been worsening. I think I may have narrowed down, but I want your input as I've just been doing a lot of forum reading and don't have much technical/diagnostic experience.

When I start the wrangler (cold), it chugs and chugs but doesn't actually start. Then I flip the key to "off," then try again and it starts up fine. If I have driven my car, turn it off, then turn it on within 5 minutes it will start up fine. When I do cold start, the jeep shakes a bit unless I push on the pedal a little bit. I also have to let it warm up b/c if I don't it will shake when I accelerate (for only about 30 seconds). Otherwise, it drives perfectly without any issues. The check engine light comes on intermittently once every 3-4 days. The code reads: P0301 = misfire cylinder one. I already changed the spark plugs, but to no avail. I was reading it may be either spark plugs, spark plug wires, distributor cap and rotor, or ignition coil.

Is it more likely to be the ignition coil (I'm assuming given the poor startup), or should I start off by changing easy things like the wires and distributor cap/rotor first?

Thank you! Your help is much appreciated.

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Old 01-13-2014, 05:46 AM   #2
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What size motor do you have. If its the 4.0 then there are no cap rotor or wires.

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Old 01-13-2014, 11:06 AM   #3
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I have a 4.0. So no cap, rotor, or wires? Hmm I guess that narrows it down some. Does it sound like it may be the ignition coil?
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Old 01-13-2014, 11:16 AM   #4
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I would clean the IAC valve and see if that helps with the idle. As far as the long starts go, it is fairly common for the anti-drainback valve to fail in the fuel pressure regulator. Turn the key on then off a couple times before cranking and likely it will start as soon as you crank it.
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Old 01-13-2014, 11:33 AM   #5
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Hey Big Sarge, thanks for the input. Yes that does help. Would this mean that the entire fuel pump regulator has to be changed? As far as I understand, that is a long process and I just want to make sure I'm not missing anything simpler before I go there.
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Old 01-13-2014, 11:43 AM   #6
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Yeah it is the fuel pressure regulator on the pump assembly. While it can be changed seperately from the pump assembly, most people change the whole thing as it does require dropping the fuel tank. I would not be in a big rush to change it though unless you start experiencing other related problems. I have heard tell of people cycling the key up to 10+ times to avoid changing it, however I personally would change it before I cycled the key 10+ times before being able to start.
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Old 01-13-2014, 11:51 AM   #7
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Your hard starts are most likely due to a very common TJ problem. There is a check valve in your fuel pump that is supposed to maintain fuel pressure while the jeep is off. These valves often go bad allowing fuel to drain back into the tank therefor allowing the pressure to drop below what the engine needs to start. Next time you go to start your jeep, try cycling the key on off on off on a few times and I bet it'll fire right up. This basically primes the system and rebuilds fuel pressure. As for your P0301 code, there are a few possibilities. What plugs did you install? The other thing is to see if your injector on the #1 cylinder is function right. Take a screw driver and touch the tip to the #1 injector and place your ear in the handle. You should hear a ticking noise. This is the injector opening and closing. Now listen to a couple of the others. Compare what you heard in #1 to the rest. If the ticking in #1 is faint compared to the others, or there's no ticking at all, you have an injector that's dirty or broken. Looking at fuel trims (if you have a scan tool) can help diagnose this too, but a screw driver and an ear drum will also work. This was the cause of the intermittent cyl 1 misfire on my 04. Hope this helps and good luck!!
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Old 01-13-2014, 12:01 PM   #8
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This is great information. Rubicon, about 1 month ago I decided to try fuel injector cleaning fluid and it helped resolve this issue for about 2 days. Then the problem returned. I'll check my fuel injectors today and post up the results. Thank you!
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Old 01-13-2014, 12:10 PM   #9
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Quote:
Originally Posted by californiawrangler View Post
This is great information. Rubicon, about 1 month ago I decided to try fuel injector cleaning fluid and it helped resolve this issue for about 2 days. Then the problem returned. I'll check my fuel injectors today and post up the results. Thank you!
No problem and yes please let us know what you find!

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