Question to anyone who can help. I have about 1500 miles on a new 4.0, new sensors, everything, high flow cat, Borla exhaust, header, K&N. I'm still getting the same gas mpg as with the old motor. I have thought about replacing the fuel pump, maybe clogged, computer. I have an 88 XJ with the AW4, 33" swampers. About this time last year it was getting 325 to a full tank on the highway, now with the new motor and old motor before, at best 210 on the highway. Killing me with gas. Any help please before I sink more money into this. Thanks Juice
-
Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.
gas mileage
- Thread starter juicexj24
- Start date
Manuel
NAXJA Forum User
- Location
- Lomita, CA
Did you just move up to the 33" tires?
If you did that and didn't recalibrate your speedometer, that would mean you're covering a lot more miles than your odometer shows.
Manuel
If you did that and didn't recalibrate your speedometer, that would mean you're covering a lot more miles than your odometer shows.
Manuel
Manuel
NAXJA Forum User
- Location
- Lomita, CA
The fuel pressure regulator might be bad.(allowing too much pressure to the injectors, so you're running rich) Your oxygen sensor could be bad also.
You could have a vacuum leak too. Check the hoses and connections to the MAP sensor. Replace any cracked or hard hoses.
Manuel
You could have a vacuum leak too. Check the hoses and connections to the MAP sensor. Replace any cracked or hard hoses.
Manuel
gas mpg
I have had the 33" for two years now, so that is why I'm at a lose with the gas. I only drove the Jeep about 3500 miles from Aug to Jan until I replaced the engine. At the time I just thought it was something to do with the high miles and waited to replace everything. Everything is new, same old problem. But the ring and pinion is still the same, speedo gear is the same as stock. Just losing 100 miles to the tank on the highway, can't really tell about around town. but about 185 to the full tank.
I have had the 33" for two years now, so that is why I'm at a lose with the gas. I only drove the Jeep about 3500 miles from Aug to Jan until I replaced the engine. At the time I just thought it was something to do with the high miles and waited to replace everything. Everything is new, same old problem. But the ring and pinion is still the same, speedo gear is the same as stock. Just losing 100 miles to the tank on the highway, can't really tell about around town. but about 185 to the full tank.
Manuel
NAXJA Forum User
- Location
- Lomita, CA
I'd say to check the vacuum lines and find out what the fuel pressure is that the regulator is providing.
Good Luck.
Manuel
Good Luck.
Manuel
- Location
- Westminster, SoCal
also take ito the account that a new part doesn't necessarily have to be good 
I learned that on more then one occassion a hard way.....
I learned that on more then one occassion a hard way.....Art Garcia
NAXJA Forum User
- Location
- Monterrey, Mexico
Let use your XJ and check mileage after his first 5000 miles and 2 oil changes
Judd W. VA
NAXJA Forum User
- Location
- new Hope, Va
That IS bad mpg........
Something is seriously amiss. That has to be translating to excessive emissions and really heating up the new cat. Will destroy the cat too if getting too hot. Is not too hard to ck the output of the O2 sensor with a DVOM if you want to see if it is registering an overly rich condition...which i'd certanly would think it should be!!
I might also think of going to an actual shop with some actual diagnostic equipment for a quick diagnostic. A mere $69 and an hour might point you in a quick direction very easily. If this happens that $69 cost disapears into increased fuel mileage awfully quickly!!!!
However, look also to a brake dragging problem or other just in case........
Something is seriously amiss. That has to be translating to excessive emissions and really heating up the new cat. Will destroy the cat too if getting too hot. Is not too hard to ck the output of the O2 sensor with a DVOM if you want to see if it is registering an overly rich condition...which i'd certanly would think it should be!!
I might also think of going to an actual shop with some actual diagnostic equipment for a quick diagnostic. A mere $69 and an hour might point you in a quick direction very easily. If this happens that $69 cost disapears into increased fuel mileage awfully quickly!!!!
However, look also to a brake dragging problem or other just in case........
thanks
I just drop my XJ off at the dealer to check it out. I just passed emissions last Tuesday so I'm fine on that end. I didn't think about the brakes, I know the front calipers are way old and didn't open that easy to replace the pads months ago. Thanks. Good idea
I just drop my XJ off at the dealer to check it out. I just passed emissions last Tuesday so I'm fine on that end. I didn't think about the brakes, I know the front calipers are way old and didn't open that easy to replace the pads months ago. Thanks. Good idea