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Old October 15th, 2019, 17:24
paulhead's Avatar
paulhead paulhead is offline
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Re: Bad gas mileage 10-11 MPG

Originally Posted by kastein View Post
Your temp gauge on a 96 and earlier uses a separate sender from the ECU, so that doesn't really rule anything out, unfortunately.

87-90 4.0: 3 temp sensors
- 1 in the left radiator end cap to turn the electric fan on (HD cooling option only)
- 1 in left side of block low down for the ECU
- 1 in the back left side of the head on the top for the gauge

91-96 4.0: 2 temp sensors
- 1 in the thermostat housing for the ECU, which now also controls the fan
- 1 in the back left side of the head on the top for the gauge

97+ 4.0: 1 temp sensor. It's in the thermostat housing and the ECU controls the fan as well as sending the data to the instrument cluster

Honestly it sounds like you've gone through most stuff. If there is even a small crack in the exhaust manifold - very common at the 2 to 1 collector - it will suck in air in between exhaust pulses and this will cause the O2 sensor to read leaner than it should no matter how much fuel the ECU dumps in to compensate, because that air doesn't ever meet the extra fuel in any meaningful way until they both end up in the catalytic converter. I've seen an XJ get single digit fuel economy due to this problem and jump to 15-16 after it was fixed.
cool thank you, will check it out
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Old October 16th, 2019, 00:50
ijeeep ijeeep is offline
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Re: Bad gas mileage 10-11 MPG

Other things that eat milage: less than perfect ground connections, the sensors need excellent ground connections all the way back to the ECU or else the signals are weak and the ECU responds by richening the mixture. ( poor grounds are why the headlights get dim as XJs age ). Dragging fan clutch will eat a few mpg too.
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Old October 16th, 2019, 08:14
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denverd1 denverd1 is offline
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Location: Tyler, TX
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Re: Bad gas mileage 10-11 MPG

Originally Posted by blu3fan View Post
I hate to tell you this.
but with the 35's and the lift. 10 mpg sounds right.
my stroker gets 8-12 city almost 20 highway. Im running 32's
Agree, I don't think it's that far off

Although new plugs HAVE to help

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Chili Pepper '98
4.5" lift, locked on both ends, 33s
10K winch and a lot of skinny pedal
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