Multiple cylinder misfire!!! - JeepForum.com

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post #1 of 71 Old 10-03-2013, 09:19 AM Thread Starter
SpecialTwinky
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Multiple cylinder misfire!!!

I'm pretty sure that this has been discussed multiple times but I can't find what I am looking for. I have a 2002 jeep wrangler Sahara. It has a straight six and cylinders 1 3 4 5 &6. I can't figure out why it is doing it. I have changed the plugs and changed the ignition coil rail. I have also checked the cylinder compressions and they are all good. Does anybody know how I can fix this problem? Thanx for your help.

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post #2 of 71 Old 10-03-2013, 11:16 AM
jkp
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Check the crank position sensor. That's what the computer uses to fire the ignition at the correct time.

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post #3 of 71 Old 10-03-2013, 03:25 PM Thread Starter
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What do I need to do that? I have never checked a sensor before.
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post #4 of 71 Old 10-03-2013, 03:58 PM
jkp
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I think you can use an ohmmeter and test the resistance to see if it's shorted.

Other than that, there's not a good way to check it that I know of.

If it's the original one, I'd replace it.

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post #5 of 71 Old 10-03-2013, 06:35 PM
TJJP77
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You would need access to an oscilloscope to check the output of the CPS and verify that the signal has the proper "waveform" to diagnose it properly.

Chris
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post #6 of 71 Old 10-03-2013, 08:42 PM
silver97tj
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Hi all

Quick and dirty. wait till night and pop hood open, startup if is arcing you will see it right away..............................

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post #7 of 71 Old 10-03-2013, 08:55 PM
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Quote:
Originally Posted by silver97tj View Post
Hi all

Quick and dirty. wait till night and pop hood open, startup if is arcing you will see it right away..............................
Little harder on an '02 - it doesn't have plug wires to arc. While it's possible to get some arcing from the coil to plug boots, it's not terribly likely if the coil rail is installed properly and the boots aren't torn or damaged.

Chris
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post #8 of 71 Old 10-03-2013, 09:07 PM
goodwrenchdave
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So i'm assuming your setting p0300 at least and since you know the cylinders p0301,303,304,305,306? any others??
pull a sample of your gas from your fuel rail into a glass and let it sit for 1/2 hour. any contaminants, water? is it murky or clear, Do you have access to a scanner? can you check exhaust backpressure...it can cause misfires.
Do you drive it nice or hard.

how long have you had these misfires. any particular condition for them happening? highway speed, under acceleration, idle , hot , cold?

mileage please
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post #9 of 71 Old 10-03-2013, 09:42 PM Thread Starter
SpecialTwinky
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I just naught the jeep and it started misfiring a week or two after. I changed the rail and drive it around for thirty minutes that same day and it was fine. When I jumped in it the next day it happpened. It usually happens around twenty minutes of driving at any speed. It has just over 120k. I took it to a mechanic and he didn't know what was wrong. He said the wiring looked good to the ignition coil.
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post #10 of 71 Old 10-03-2013, 09:42 PM Thread Starter
SpecialTwinky
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Bought not naught. Sorry
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post #11 of 71 Old 10-03-2013, 09:45 PM
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What type of plugs are in it now and what brand?

Usually a Crank senser works or it dont. Since it does run I would assume that its ok.

How much fuel pressure you got?
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post #12 of 71 Old 10-03-2013, 09:51 PM
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Have you thrown a cel and if so what were the codes?Your stating a multiple miss fire but nothing on a code?You need to elaborate a bit more.Is this a manual or an auto?
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post #13 of 71 Old 10-03-2013, 10:22 PM
goodwrenchdave
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Do you have a warranty as you just bought it?

sounds almost like it was sold because of this problem.

reading material.... not saying it's this as it has to be diagnosed but:

http://www.wjjeeps.com/tsb/tsb_wj_0900303.pdf
remember this can get expensive fast!

A very simple check is to just decarbonize first and check results.
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post #14 of 71 Old 10-04-2013, 06:47 AM
aTX427
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Run old school standard copper plugs, buy some Mopar wires, change the CPS with a Mopar sensor and check your ground straps. Stay away from the fancy plugs and cheap Chinese sensors.
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post #15 of 71 Old 10-04-2013, 10:31 AM Thread Starter
SpecialTwinky
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I just put brand new Bosch Double Platinum plugs. The codes were p0300 301 303 304 305 306. What are mopar wires and how do I change them? And it is an automatic
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help please , misfire cylinder 6 , sahara

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