Poor MPG's.........= frustrated

X Factor · Mar 13, 2005

need some good advice on why my Kee is getting just plain awful MPG.
i'm lucky to get 180 miles out of a tank.
had a tuneup this past fall, w/new air filter as well. truck is completely stock except for 235 MT/R's. MPG's were almost as bad w/the old stock size car tires. i don't believe the tires are to blame. i'm atta loss......

rdx4me · Mar 13, 2005

I know how you feel... I have a 90 XJ 4.0 and I might as well be driving around in 4WD all the time. Mileage is around 10-12mpg regardless of tune-up's or anything.

mack · Mar 13, 2005

dude! i wish i was gettin 180k from a tank, i filled it to the point of overflow,and all i got was 130k!!! talk about frustrated! at $205 a gallon!

Kejtar · Mar 13, 2005

X Factor said:
need some good advice on why my Kee is getting just plain awful MPG.
i'm lucky to get 180 miles out of a tank.
had a tuneup this past fall, w/new air filter as well. truck is completely stock except for 235 MT/R's. MPG's were almost as bad w/the old stock size car tires. i don't believe the tires are to blame. i'm atta loss......

1. what tires did you have to start with? and did you change your speedo? Your calculations are probably way off now.

2. what engine? what year? how many miles on the engine, you have to give more details.

johnnyc · Mar 13, 2005

mack said:
dude! i wish i was gettin 180k from a tank, i filled it to the point of overflow,and all i got was 130k!!! talk about frustrated! at $205 a gallon!

You're getting 130,000 per tankful!?! And paying $205/gallon??

ChuckD · Mar 13, 2005

Man you guys don't know nothing. Just change your speedo gear in your t-case so that you can get all the miles you want on that odometer!

Simple Mod, I did it and I get over 25 mpg, and that's with 33's and 4.88's! :laugh3:

bustednutz · Mar 13, 2005

I run 235's on my 98 Sport. Keep those suckers inflated to 32 PSI or a little more. I do and I get about 350 miles to the tankful. Prior to the bump up in tire pressure I was getting about 260 miles per tankful.
Give it a try. Previous pressure was around 25 PSI. Much smoother ride with softer tires, but with gas prices going through the roof I'll suffer a little on ride comfort.

mack · Mar 13, 2005

:laugh3: oops....130 miles and $2.05....:dunce:

xjohnnyc said:
You're getting 130,000 per tankful!?! And paying $205/gallon??

rdx4me · Mar 13, 2005

Not...

JoBo · Mar 13, 2005

OK guys, on the RENIX systems there is no check engine light. Therefore you don't know when the o2 sensor is bad. My son's stock 89 was getting around 10 mpg in the city. We replaced the o2 sensor with a new Bosch one and the mpg's went up to 17-19 mpg. The engine also has more power and runs better. When I put a new cat on my 96 I also replaced both o2 sensors (DENSO brand) and my highway mps was 22 two tankfulls in a row. My CEL was not on but they were tired.

JoBo

X Factor · Mar 13, 2005

Kejtar said:
1. what tires did you have to start with? and did you change your speedo? Your calculations are probably way off now.

2. what engine? what year? how many miles on the engine, you have to give more details.

97, 4.0/auto, 117k and 3.55's. don't remember what stock size was. but there isn't much of a difference between the 2 sizes, mpg wise.

had the O2 sensor replaced at same time of tuneup, it went bad first.

i'm almost thinking the converter might be clogged. that's really the only thing i havne't checked

mudpuddle · Mar 13, 2005

I notice a big difference in using "winter fuel". Whatever the blend is, it sucks for MPGs. I average around 13mpg in the city, probably around 20 on the highway, but in the summer both figures jump up around 3mpg. I'm running 235/75-15 Cooper ATs, 3.55 gears and fresh tune up. Keeping the psi around 33 definetly helps too.

CheapXJ · Mar 13, 2005

champion truck plugs or NGKs (do NOT run any of them platinum double triple quadruple eleventybillion electrode sparkplugs)
192* thermostat
get some GM top engine cleaner and run that through.

from there, check for vacuum leaks

make sure you get a cap+rotor with brass contacts (shop around till you find one, or go to the dealer)

casm · Mar 13, 2005

CheapXJ said:
champion truck plugs or NGKs (do NOT run any of them platinum double triple quadruple eleventybillion electrode sparkplugs)

I'll second this... Having run them in my cars for years with no adverse effects, I put Bosch Platimum +2s in my 2001 about 10,000 miles after I bought it. Fuel consumption went from an average 16/22 to about 14/18. Yanked the plugs after three tanks of gas, replaced them with OE Champions, fuel economy recovered. YMMV, but it seems like XJs work best with what's been recommended.

MachineMan · Mar 13, 2005

Did you re-gap those Champion plugs? The XJ Haynes manual says 0.035" but they came gapped about 0.044" out of the box. I put them in anyway without regapping them.. Im still wondering if I should have??

casm · Mar 13, 2005

MachineMan said:
Did you re-gap those Champion plugs? The XJ Haynes manual says 0.035" but they came gapped about 0.044" out of the box. I put them in anyway without regapping them.. Im still wondering if I should have??

I honestly don't remember whether or not I did re-gap them. In general, though, it's usually best to set them to whatever the FSM recommends. I've no idea where the Haynes manual got that 0.035" value from, but Section 8D, page 11 of the 2000 FSM gives the same number for the plug gap on both the 4- and 6-cylinder engines. Bear in mind that this may well vary depending on the year of your XJ.

Poor MPG's.........= frustrated

X Factor

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