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Old 12-17-2014, 05:24 PM
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3.8 L knock

I have a friend with a 2011 Wrangler V6 and he has to use 91 octane gas or it knocks under load. If he runs the 87 fuel it will knock when under load. The dealer just said to run the 91 but that engine shouldn't have to have this, right? If the knock sensor wasn't working, wouldn't it set a CEL code?

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Old 12-22-2014, 02:28 AM
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Re: 3.8 L knock

That engine is rated for 87 octane, so the dealer is literally full of crap. If he's been running 91 for a while, the engine will knock for a bit when it transitions back to 87 as the computer readjusts the ignition timing to compensate for the less resistant fuel. This happens anytime you switch from high to low octane and vice versa. It can take a while sometimes, but ideally the computer should be able to adjust.

If it keeps having problems, however, there is most likely a more serious problem with the engine itself. It may run on the 91 for a while, but its only a matter of time before the problem worsens.
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Old 12-30-2014, 03:15 PM
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Re: 3.8 L knock

If he has a lot of mileage on it... it might need a tune up. Just did mine and it helped. 08 JKU at 90k
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Old 12-31-2014, 12:59 PM
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Re: 3.8 L knock

Thanks for the reply. What, exactly, did you do for the tune up?
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Old 01-01-2015, 06:15 AM
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Re: 3.8 L knock

I'm sure changing the spark plugs and coils/wires would probably be a big help. Also, depending on how high mileage it is, it may even need new fuel injectors. Not quite sure if that would be related to the knocking from low octane fuel, but it might not be a bad idea (Anyone with more experience in engine performance would probably know more than I do about that).
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Old 01-08-2015, 09:43 PM
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Re: 3.8 L knock

I replaced plugs and wires on my 07 Rubi this fall. Close to 100K when I did it, made a very noticeable difference in the engine smoothness and pull. If it has a lot of miles on it I would definitely start with a tune up.

Jerry S.
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Old 01-17-2015, 02:33 PM
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Re: 3.8 L knock

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Originally Posted by Jerry Slaughter View Post
I replaced plugs and wires on my 07 Rubi this fall. Close to 100K when I did it, made a very noticeable difference in the engine smoothness and pull. If it has a lot of miles on it I would definitely start with a tune up.

Jerry S.
Yep. Bought my 08 in Oct 07 so the combination of miles and age take a toll. I did not put anything special, just OE rated plugs and wires. It helped.
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Old 01-31-2015, 01:10 AM
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Re: 3.8 L knock

It was designed to run on 87 Octane.

It sounds like it just needs a good tuneup, along with some Chevron Techron fuel injector cleaner.....
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