2003 JL 4 Wd 3.7 L V6 - JeepForum.com
 
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post #1 of 5 Old 06-16-2019, 07:10 AM Thread Starter
Kimwillis
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2003 JL 4 Wd 3.7 L V6

P0300 and all cylinders misfires at 60 mph ???

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post #2 of 5 Old 06-18-2019, 07:05 PM
02blue
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When were the plugs changed last?

"Hey, ya never know til you try." Kurt Russell-Big Trouble in Little China
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post #3 of 5 Old 06-19-2019, 10:32 AM
Brad426
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What does the code mean?
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post #4 of 5 Old 06-19-2019, 08:21 PM
02blue
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Quote:
Originally Posted by Brad426 View Post
What does the code mean?
Random misfire. I always start by checking the plugs. These copper cores don't last much more than 30k. Could also be low fuel pressure or many other things that would not limit the misfire to specific cylinders.

"Hey, ya never know til you try." Kurt Russell-Big Trouble in Little China
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post #5 of 5 Old 06-20-2019, 01:15 PM
Brad426
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I've been bending wrenches for over 45 years and my experience with spark plugs has been KISS. Don't waste your money on fancy crap or BS ads. Use what the OEM calls for. Believe it or not I have had the best luck over the years with plan old replacement NGK spark plugs.
Here's what I would try. If the plugs or a plug is/are breaking down a 60 MPH. Drive it at 60 mph for awhile with the misfire. turn the engine off in flight, cost to a stop and pull the plugs out and have a look. You need to catch the crime in the act. If you slow down with the engine running the colour of the plugs will change. The dyno is the safest place to did this but, non busy back roads are good too. Fuel pressure is easy to test with a gauge. At this stage it's hard to say what is going on. Start with a fresh set of plugs.
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