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Help with #3 misfire P0303

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Old 06-02-2016, 12:30 PM
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Originally Posted by EHarris
Ok glad to know it's the same on other peoples vehicle.

I did buy the coil pack already but I figured might as well replace it since I plan on driving the JK to 200k with the lifetime powertrain warranty.

Do others have experience with bad coil packs or is this definitely a waste of $$ and I should go return it.
It's not a common repair; but I've seen a couple over the years...
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Old 06-02-2016, 02:30 PM
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Replaced plug #3. Problem seems to be solved!!! Here is the old one.
Attached Thumbnails Click image for larger version Name: image-737370577.jpg Views: 140 Size: 587.0 KB ID: 648660  
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Old 06-02-2016, 02:49 PM
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Default Help with #3 misfire P0303
Good news!
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Old 06-02-2016, 03:01 PM
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Originally Posted by Kerberos
Good news!
Thanks so much for the help. I know it's not the greatest picture but what is wrong with that plug?
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Old 06-02-2016, 03:34 PM
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Originally Posted by EHarris
Thanks so much for the help. I know it's not the greatest picture but what is wrong with that plug?

Doesn't look fouled. Gap is probably too wide. That's why it helps to look at the plugs first. It can save you a ton of time, back & forth, etc.
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Old 06-02-2016, 03:42 PM
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Originally Posted by DJ1
Doesn't look fouled. Gap is probably too wide. That's why it helps to look at the plugs first. It can save you a ton of time, back & forth, etc.
Or....

Click image for larger version Name: Screen Shot 2016-06-02 at 4.38.59 PM.png Views: 164 Size: 380.4 KB ID: 648662
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Old 06-02-2016, 04:03 PM
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Originally Posted by EHarris
Thanks so much for the help. I know it's not the greatest picture but what is wrong with that plug?
If that's a platinum plug (fairly sure) then the electrode is almost completely gone...

You're probably going to be doing the other 5 soon.
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Old 06-02-2016, 04:30 PM
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Originally Posted by DJ1
Doesn't look fouled. Gap is probably too wide. That's why it helps to look at the plugs first. It can save you a ton of time, back & forth, etc.
The gap was at .060

Lessons learned here for sure.
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Old 06-02-2016, 06:42 PM
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Originally Posted by EHarris
The gap was at .060

Lessons learned here for sure.
Normal gap is 0.050".

One thing to keep in mind if a coil pack is suspected of being the cause of a misfire...
Each coil in the pack fires two plugs. If the coil was the cause of a #3 misfire, for example, #6 would also be misfiring.
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Old 06-02-2016, 06:45 PM
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Originally Posted by ronjenx
Normal gap is 0.050". One thing to keep in mind if a coil pack is suspected of being the cause of a misfire... Each coil in the pack fires two plugs. If the coil was the cause of a #3 misfire, for example, #6 would also be misfiring.
Thanks Ron. I will definitely remember that one. Good piece of information.
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