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  #16  
Old September 13th, 2019, 20:10
CJ'sXJ CJ'sXJ is offline
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Re: Bad gas mileage 10-11 MPG

I didn't see it mentioned, pull the vacuum line to the fuel pressure reg. These are known to slowly lose the diaphragm and start leaking into the vacuum line. If it's gone you will have raw fuel in the line. Good luck getting it figured out!
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  #17  
Old September 13th, 2019, 23:04
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Re: Bad gas mileage 10-11 MPG

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Originally Posted by CJ'sXJ View Post
I didn't see it mentioned, pull the vacuum line to the fuel pressure reg. These are known to slowly lose the diaphragm and start leaking into the vacuum line. If it's gone you will have raw fuel in the line. Good luck getting it figured out!
location of pressure regulator?
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Last edited by paulhead; September 13th, 2019 at 23:10.
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  #18  
Old September 13th, 2019, 23:09
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Re: Bad gas mileage 10-11 MPG

Also how do you use propane or smoke? Assume propane getting sucked in vacuum leak and increasing idle? Sorry, don't know.
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  #19  
Old September 16th, 2019, 09:36
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Re: Bad gas mileage 10-11 MPG

I've never had luck using propane or the like to find smaller vacuum leaks. I built a smoke tester for about 50 dollars and love that thing. I found a few very small pinhole leaks using that device.

Here's one example.

https://www.youtube.com/watch?v=Np_duzsaZxI

Here's the one I built which was a little more hack job than others haha. I used a tube of epoxy for all the fittings. If I build another one I'll put the fittings in the side instead of the lid.

https://www.youtube.com/watch?v=29oXZ1sFPEY
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Last edited by devildog0; September 16th, 2019 at 09:40.
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  #20  
Old September 20th, 2019, 13:31
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Re: Bad gas mileage 10-11 MPG

So I finally got around to messing with the jeep, meanwhile thank you guys for flooding me with answers. Some suggested that O2 sensors could be bad and not read codes. So I ran am OHM test across the 2 white wires on the sensor and got 3.5 which is below specs. Gonna swap it out and see what happens.
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  #21  
Old September 20th, 2019, 13:36
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Re: Bad gas mileage 10-11 MPG

Also do I need to unplug the battery and reset the brain or anything?
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  #22  
Old September 20th, 2019, 13:54
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Re: Bad gas mileage 10-11 MPG

Yes, that is worth doing. Disconnect both battery terminals and touch the cables together for 5-10 seconds.
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  #23  
Old September 20th, 2019, 16:16
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Re: Bad gas mileage 10-11 MPG

Make sure to buy NTK/NGK O2's and NOT Bosch.
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  #24  
Old September 20th, 2019, 16:26
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Re: Bad gas mileage 10-11 MPG

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Make sure to buy NTK/NGK O2's and NOT Bosch.
Done and installed
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  #25  
Old September 23rd, 2019, 23:18
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Re: Bad gas mileage 10-11 MPG

1/2 tank of gas later and same, 10 mpg. Blew a hole in my muffler this morning and replaced it with a Flowmaster. Could a crappy muffler affect mileage? Didn't' notice a power difference after the switch so I don't think it was choking it.
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  #26  
Old September 24th, 2019, 08:01
RCP Phx RCP Phx is offline
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Re: Bad gas mileage 10-11 MPG

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1/2 tank of gas later and same, 10 mpg. Blew a hole in my muffler this morning and replaced it with a Flowmaster. Could a crappy muffler affect mileage? Didn't' notice a power difference after the switch so I don't think it was choking it.
Not to likely but a clogged cat will.
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  #27  
Old September 24th, 2019, 08:01
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4x4JeePmaNthINg 4x4JeePmaNthINg is offline
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Re: Bad gas mileage 10-11 MPG

I've read a bad catalytic converter can, but are you noticing acceleration problems to?
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  #28  
Old September 24th, 2019, 08:14
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Re: Bad gas mileage 10-11 MPG

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Check the basics, …... Nearly all XJ's have or will have a cracked exhaust manifold.
That would run rich.
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Quote:
Originally Posted by bimmerjeeper

Go ahead and slam the liftgate down on a blanket, and see how long you are laughing.
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Tim MAY be 100% correct, but why would a person automatically pick him as the expert .....
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  #29  
Old September 24th, 2019, 10:57
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Re: Bad gas mileage 10-11 MPG

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Not to likely but a clogged cat will.
dude inspected cat and said it was good. back to the drawing board
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  #30  
Old September 24th, 2019, 12:55
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Re: Bad gas mileage 10-11 MPG

Could a bad temperature sensor be a possibility? Just spit balling.
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