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Old 07-16-2014, 11:43 PM   #1
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Worse gas mileage

Hey guys. I glanced around a little and didn't see any threads about this. I changed my spark plugs in my 06 rubicon. Since then, I'm getting a little worse of gas mileage and unless it's my imagination, a rough idle every now and then. I am getting about 12-13 mpg with highway/street combined, and was getting about 13-14. I have a 4" lift with 31s as well. Is this normal for everyone else?

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Old 07-17-2014, 12:30 AM   #2
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Did you put in different brand plugs? Do a search--there are a variety of opinions on plugs. Factory were probably NGK for that year. Some people stick with those, some use Champion, some Autolite, etc. You may find that for YOUR Jeep one type might perform better. I put Champion in my 2004 and mileage is good (18-20) for my stock Jeep but it has a bit of a rough idle until it warms up.

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Old 07-17-2014, 12:32 AM   #3
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I installed the autolite APP985 platinum tips spark plugs
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Old 07-17-2014, 12:55 AM   #4
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Question

Did you gap to .035? If so, maybe your ride just don't like those plugs. Or, it's something else . . .
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Old 07-17-2014, 02:28 AM   #5
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I get about 190-240 per tank. Not great at all. I have 33x12.5x15's. 4.5" lift with 1" BL.
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Old 07-17-2014, 05:36 AM   #6
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I have a hardtop LJ with a heavy 8274 winch and plate up front. 3.73 gears, 4spd AT, 31" KM2's. New plugs, new filters, new oil, new o2 sensors, new fluids everywhere. I get 12-13 mpg everywhere I go. I have timed miles to determine that I'm 3.5% off on my speedo which would add almost .5 mpg, which I find negligible. I am heavy(ish) footed and I see mostly freeway at the moment.

I only saw 14-15 with all new everything on my '99 soft top, so I've determined that these folks that claim 18-20 mpg are either calculating wrong, or are driving in a manner that would make me rather ride the bus.
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Old 07-17-2014, 08:00 AM   #7
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The APP985 is a very good plug choice, maybe you have an upstream 02 sensor (there are two) starting to go out. When they go bad, they wreck the air-fuel ratio which can destroy the power and mpg.
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Old 07-18-2014, 10:24 PM   #8
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I use autolite platnimums as well and routinely get 17 - 18 mpg and I am confident that it is pretty accurate. Have 31" tires and 3" lift + 1" bl. 5 speed with 3.73 gears.
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Old 07-19-2014, 08:55 AM   #9
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It could be general variation. How many tanks worth of data is this? I have 108 tanks worth of data and it ranges from 8 to 16 mpg with an average of 13.3
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Old 07-19-2014, 10:48 AM   #10
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I get like 12 to 13 with 3.73 gears and 33s with a 4 inch lift. Does and intake and exhaust help? I am thinking of a tuner to even though in Cali they are not technically legal. Love my Jeep, hate the mileage.
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Old 07-19-2014, 11:18 AM   #11
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Quote:
Originally Posted by Jerry Bransford View Post
The APP985 is a very good plug choice, maybe you have an upstream 02 sensor (there are two) starting to go out. When they go bad, they wreck the air-fuel ratio which can destroy the power and mpg.
I had a similar experience and it was one of the O2 sensors.
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Old 07-19-2014, 12:55 PM   #12
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Quote:
Originally Posted by JDWranglerGuy View Post
Does and intake and exhaust help?
No.

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