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OEM Tech Discussion Forum for OEM (Original Equipment) or stock XJs and MJs. |
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#1
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Bad gas mileage 10-11 MPG
I know a common problem but wouldn't mind some input. 1992 4.0 AW4, 4.88s, 35s. Fuel lines and rails were redone before sold to me so it could pass smog which it did easily. I've had jeeps before and I know it shouldn't be this bad. One thing I've noticed is it's shifting weird likes it's floating between gears once in a while. It was doing this really bad before but I replaced the TPS and it's normal now but still doing it very slightly.
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“Lead me, follow me, or get out of my way. ” -Gen. George S. Patton Jr. Back at step 1, bought a YJ, an XJ going under the knife.... ![]() |
#2
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Re: Bad gas mileage 10-11 MPG
What have you done to check the motor(comp check, vacumm, spark plugs, coil, wires, and timing)? I'm getting 16mpg with a high hp stroker!
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#3
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Re: Bad gas mileage 10-11 MPG
No codes, plugs and wires are fairly new, I guess I could check for vacuum leaks with starter fluid.
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“Lead me, follow me, or get out of my way. ” -Gen. George S. Patton Jr. Back at step 1, bought a YJ, an XJ going under the knife.... ![]() |
#4
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Bad gas mileage 10-11 MPG
Torque converter?
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#5
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Re: Bad gas mileage 10-11 MPG
Check the basics, tune-up, comp, vac leaks, manifold leaks, and then check the O2 sensors. Nearly all XJ's have or will have a cracked exhaust manifold.
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. ![]() . Quote:
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#6
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Re: Bad gas mileage 10-11 MPG
hows the power feel?
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John V. RRC VP ![]() 01 XJ Sport 2 door 5spd/4WD- 4" lift, Rubi wheels/tires JCR bumpers/sliders, armor, Rubi 44, Ford 8.8, 4.56's, ARBs. |
#7
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Re: Bad gas mileage 10-11 MPG
dragging brakes? does she roll easily in neutral?
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#8
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Re: Bad gas mileage 10-11 MPG
Interesting, not engaging 100%?
Good power yeah, thought about brake drag too, not noticing it.
__________________
“Lead me, follow me, or get out of my way. ” -Gen. George S. Patton Jr. Back at step 1, bought a YJ, an XJ going under the knife.... ![]() |
#9
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Re: Bad gas mileage 10-11 MPG
Ever pulled the distributor cap and looked inside?
Don't use starting fluid to check for vacuum leaks. It can travel whereas carb cleaner and brake cleaner stay a liquid much longer. A common issue is loose intake manifold bolts. Snug them up as needed. The vacuum line from the intake manifold to MAP sensor is critical. any slight leak and the fuel mixture goes richer. |
#10
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Re: Bad gas mileage 10-11 MPG
Regarding the transmission still shifting funky after the TPS swap - has the transmission fluid and filter been changed recently?
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#11
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Re: Bad gas mileage 10-11 MPG
Run a can of BG44k through the fuel to clean out the carbon and the injectors. Old clogged injectors is one of the most common things for crappy gas mileage.
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Tom Houston - Former Colorado Chapter Treasurer , Terminal Adrenaline Junkie, and Rocket Scientist Loveland, Colorado My teardrop build You're just jealous because the voices don't talk to you. ![]() |
#12
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Re: Bad gas mileage 10-11 MPG
torque converter clutch not engaging will do it for sure, since without the clutch you are relying on hydraulics alone. if you feel like the trans is shifting weird I would probably start there.
check for fuel leaks / damp fuel lines (no kidding) use the key trick to pull codes and see if anything there that didn't trip the CEL are you running a 180 or 165 thermostat? the computer tries to get the engine temp to 195 by running a rich mixture so that the cat converter works efficiently, if temp stays low the computer will forever be dumping unnecessary fuel. O2 sensor can do it too but not usually that aggressive |
#13
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Re: Bad gas mileage 10-11 MPG
Quote:
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“Lead me, follow me, or get out of my way. ” -Gen. George S. Patton Jr. Back at step 1, bought a YJ, an XJ going under the knife.... ![]() |
#14
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Re: Bad gas mileage 10-11 MPG
Ive had my intake man fail to seal multiple times. I would start by using a propane torch off. and searching the engine bay.
or you could use smoke. whatever floats your boat. if its a vacuum leak it will show. |
#15
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Re: Bad gas mileage 10-11 MPG
otherwise fuel pressure test.
then check spark. |
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