P0301 and P0300 Codes. running out of crap to change - JeepForum.com

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post #1 of 20 Old 07-30-2010, 02:03 AM Thread Starter
RMiksits
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P0301 and P0300 Codes. running out of crap to change

2000 Jeep wrangler Sahara. 185000 miles.

Been chasing a P0301 and P0300 (cylinder 1 misfire and random misfire) for awhile now.

What Ive done so far.

Air sensor, cam sensor, crank sensor, new coil pack, new plugs, checked cat they said it was good, 6 new fuel injectors.

I know the timing is completely controlled by the computer so it cant be bad timing. right?

I'm thinking the fuel pump now and O2 sensors this weekend. After that im at a loss. This thing cant keep its engine light off long enough to pass inspection, so I dont know what to do.

what next? Any tips you can offer to help narrow it down?

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post #2 of 20 Old 07-30-2010, 02:27 AM Thread Starter
RMiksits
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One more thought. is there suppose to be a paper spacer in the crank sensor?
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post #3 of 20 Old 07-30-2010, 07:48 AM
mikevsgeek
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I would get some schematics of the engine wiring harness and start pin testing your wiring, its possible you have a frayed wire some where, or maybe a loose ground.

And a computer can only tell you what it senses is wrong, it cant diagnose itself so if your ECU is messed up, it wouldn't have the slightest idea so that could also be a possibility
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post #4 of 20 Old 07-30-2010, 07:55 AM
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Yep. You need to check connections and wiring before you start replacing parts.

If it's worth doing, then it's worth overdoing.

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post #5 of 20 Old 10-01-2010, 10:44 PM Thread Starter
RMiksits
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Still have not figured this out. Ive taken it to 4 different mechanics now all say its running fine.
WTF? this may be an excuse for a new engine.

Got rid of the p300 now its only p301.

What on earth would cause only cylinder 1 to misfire?
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post #6 of 20 Old 10-02-2010, 04:19 PM
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Quote:
Originally Posted by RMiksits View Post
What on earth would cause only cylinder 1 to misfire?
Injector, valve spring or spark plug...
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post #7 of 20 Old 10-02-2010, 05:11 PM
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Check plug wires too, small tear at boot will cause misfire might check at night to look for any arcs
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post #8 of 20 Old 10-02-2010, 05:53 PM
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Check plug wires too, small tear at boot will cause misfire might check at night to look for any arcs
He doesn't have plug wires on his 2000 4.0L...
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post #9 of 20 Old 10-02-2010, 06:08 PM
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Quote:
Originally Posted by Knuckelhead View Post
Injector, valve spring or spark plug...
X2, try swapping injector 1 with another one, see if the misfire follows.

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post #10 of 20 Old 10-02-2010, 06:42 PM
gremlinsteve
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try starting with the basics. compression test and a leak down check. 301 is related to only one cyl. is it eating coolant? how about pictures of the spark plug from #1 cyl?

steve
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post #11 of 20 Old 10-02-2010, 07:39 PM
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Try doing a compression test to make sure you don't have a blown head gasket. And maybe try doing a leak down test to make sure you don't have a burnt valve.

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post #12 of 20 Old 10-02-2010, 08:33 PM
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Quote:
Originally Posted by Knuckelhead View Post
He doesn't have plug wires on his 2000 4.0L...
Sorry, missed the 6 cylinder part I was thinking of the 2.5L
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post #13 of 20 Old 10-02-2010, 11:22 PM
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Same here with #2 only. Any suggestions after two good compression checks and leak down within spec?

Going to swap injectors hopefully Monday. No time before then. Replaced everything in his list above as well, along with new cat, same deal.

Best of Luck,

Mike
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post #14 of 20 Old 10-03-2010, 12:57 AM
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Had this in my old XJ 4.0... Here's what I did during my gremlin chase...

Plugs
Wires
Cap
Cleaned MAP sensor
Cleaned intake
Cleaned TPS
And nothing!!!!

So here's what I found and the jeep was spitting out p0301 and p0300 constantly and had a bit of a rough idle when in gear at a stop...

It was a short in the cylinder 1 fuel injector wire harness. I simply snagged one off a newer TJ in a pull yard and the problem suddenly
stopped. It's not you're head..... Unless you're oils brown and thick. Just get yourself a long screw driver and put it on each fuel injector while it's running and make sure it's firing... You will be able to tell if it's not.

Good luck!

On my 8th Jeep now! 98' TJ 4.0L, 2.25" bb, 33" Toyo M/T's, Cragar D windows and much more to come!
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post #15 of 20 Old 10-03-2010, 12:59 AM
surfTJsnow
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Had this in my old XJ 4.0... Here's what I did during my gremlin chase...

Plugs
Wires
Cap
Cleaned MAP sensor
Cleaned intake
Cleaned TPS
And nothing!!!!

So here's what I found and the jeep was spitting out p0301 and p0300 constantly and had a bit of a rough idle when in gear at a stop...

It was a short in the cylinder 1 fuel injector wire harness. I simply snagged one off a newer TJ in a pull yard and the problem suddenly
stopped. It's not you're head..... Unless you're oils brown and thick. Just get yourself a long screw driver and put it on each fuel injector while it's running and make sure it's firing... You will be able to tell if it's not.

Good luck!

On my 8th Jeep now! 98' TJ 4.0L, 2.25" bb, 33" Toyo M/T's, Cragar D windows and much more to come!
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