ericspkl

any input would be very helpful

so i have a 99 XJ AW4

im getting about 14 in city and about 18 on highway
ive seen alot of people saying they get about 18 in the city

is 14 pretty common for my jeep?
and what are some things i can do to improve mpg's?
(besides common things, spark plugs, cap,rotor,o2 sensors etc.

Thanks!

Superslow

I got my '98 XJ about a month and 1100 miles ago. On the 250 mile trip home from where I bought it I got 19.5 mpg on the highway cruising at 72 mph. The next couple of tanks were all city driving. I averaged 12.5 mpg. Ugg...I did a tune up and no real improvement to city mileage was seen. So to try to get a handle on my poor mileage I got a Scangauge so I could monitor what was going on.

I've only had it installed a few days but I'm gaining some insight into how my driving habits really effect my mileage. Here's an example from today: I got in the Cherokee to go to the market. The engine was cold and I drove 2.8 miles to the market in about 10 minutes. The engine came up to operating temp just as I was pulling to the parking lot. I averaged 6.9 mpg for the trip...yuk! On the return trip the engine came up to temp almost immediately and in the 2.9 miles to get back home I got 15.1 mpg.

Now that is some info I can use. I've got a 500 mile trip this weekend and I plan on trying out different cruising speeds to see if I can't find the sweet spot for highway mileage.

F1Addict

You're getting average MPGs both city and highway. The best thing you can do is keep up with maintenance, especially tire pressure, and limit the use of your go pedal. My best is a 380 mile trip (from sea level to 7700 feet), got 22.5. My worst fill-up this year (no road trips yet) is 13.8, best is 17.9, average is 15.1 but I drive like a grandma, mostly.

The EPA lists the 1999 XJ (4WD, 4.0L, Auto) at 14 city and 19 highway.

Kingfisher

I once had a car that told me how my mileage was. It does make you think about and drive accordingly!

salad

So have you done those, then? Air filter clean, tire pressure correct, brakes not dragging, not carrying any weight?

ericspkl

thanks for all the replies!!

i havent done the o2 sensors but its not throwing me a check engine light
cap and rotor need to be done
plugs are new
all fluids have been replaced within 5000 miles
tires are to pressure but need new tires

DFlintstone

A bit out of my territory here. My (single) 02 sensor is about $70. It controls the final deal. I gather they fail rich, and mine did. Changing it probably was the most important thing I did to gain MPG. Mine was stone dead. You can clean your IAT. I actually installed a 200 home resistor in place of mine. Now my Puter always thinks I'm in Miami! (I'm not recommending that). Your IAT is likely all gunked up and easily cleaned.

Depending on what Salad and F1 and others think, my thought is if you don't know the history of your 02 sensor, you might make money changing it. You are Zirconium. My Titania is questionable at 60K. Even one MPG will pay it back someday.

Does 99 come with 4 hole injectors? Maybe an up-grade would help

salad

Nope no 4-hole injectors were ever stock on an XJ.

And yes the O2 sensors will start dying loooooong before you get a code. They're wear items like Flintstone says. Regular wear item.

cruiser54

I don't see plug wires on that list.................

MtnHermit

I've given up on the MPG chase, haven't checked in years. Too disappointing when I did check.

Now focus on that torquey six and the fun of power sliding on dirt roads.

krazynezz

I gave up on mileage also. Since I bought my 93 it's consistently averaged 200 miles a tank with primarily city driving. Now it's completely out the window with 35s and a welded rear end.

ericspkl

wires have not been done

i figure ill start with this
finish up regular maintenance (when the wallet allows..)
if no improvement replace all o2 sensors
then if its still not great ill replace the injectors

thank you everyone
i appreciate all the input!

Hyplox

Cut the exhaust pipe off after the cat... saved a few penguins doing that on mine.

Radi

The mileage you are getting is pretty normal. IIRC they were rated at 14/19 by the EPA when new.
You aren't going to get 18 city with a '99, those who do are probably running older XJ's with a manual and the Renix system. That combo seemed to do notably better on gas.

Turbo X_J

Carbon monoxide is bad, m'kay? Tailpipe exits at the rear bumper for a reason.