Guntar13

Okay so just ran through another full tank and wouldn't you know, ten miles to the gallon! I know Jeeps aren't hybrids when it comes to mileage but 10 is a bit rediculous! Any thoughts as to what might help be a cluprit. Repairs done in last two weeks...
plugs, wires, cap, rotor, cleaned throttle body (off the car), new TPS and adjusted, oil changed, oil leak fixed, changed both diff fluids, cleaned injectors, high flow air filter in stock box, cleaned IAC and IAT sensors, fixed bad tailpipe on exhaust, refreshed and fixed grounds

I was wondering maybe the 02 sensor? Not sure but 50-65 bucks is a lot to go out on a hunch,

XJ.89.Limited

I have an 89 limited, I gave up on fuel economy. I belive I run about 12 now, but don't quote me on that. I've done the cap, rotor, and plugs and it made a slight difference. They say run champion copper, but I had to go with champion platinum because the coppers were out of stock and I needed plugs bad. I also did an oil and filter change and air filter change, that made it a little better. I keep the tires with enough pressure in them, I have no exhaust leaks or manifold leaks, I dont know where to go next. It's getting inspected tomorrow, so that should tell me if I need an o2 sensor. Thats gonna be my next step. As far as any other things, check your fuel system. Make sure it has pressure, no leaky or clogged injectors, no leaks in general. Run a higher grade fuel in it or a system cleaner. I believe STP is good for the jeeps, but there are other threads about that. I can relate to how you feel because I have the same problem. Let me know if you discover anything.

ZINGGG

Yeah check for a cracked exhaust manifold. I'd start with the upstream o2 sensor. Even if the o2 sensor gave you a boost of one mpg, it'd pay itself off in no time

Guntar13

That's what my next step also would be is the 02 sensor, definately report back how inspection goes I would be interested to see. Thanks

Turbo X_J

Fuel Economy "is what it is", the only way to increase it is to lower mass, or increase volumetric efficiency.

For comparison in 1989 the price of a gallon of regular gas was $1.12 per gallon, not that big of deal if it got you 10 miles (about 11¢ per mile). Wait till this summer when the price goes way up. If your hurting now you may want to look at another type of vehicle.

goneboating06

My 89 is lifted 5 inches with 32x11.50 mud terrains and I get 16-17mpg in town, and about 18 on the freeway... 10mpg is ridiculous. Have you checked your catalytic converter, or ever replaced it? These jeeps are 23 years old, over time the cat looses efficiency and tends to get plugged up. Just a suggestion. The oxygen sensor is another big culprit of bad gas Milage.

EvstaG

Yeeeah I get about 24 highway mpg in my 89'... Stock of course, and a 5 speed, but still. Another thing to check would be the vacuum line running from the throttle body to the MAP sensor on the firewall. That one is quite important for how the engine runs. Good luck!

cruiser54

If the O2 sensor has never been replaced to your knowledge, I would replace it. Also do this especially in regards to the relays on your passenger side inner fender.

austinjoe13

I'd put money on a cracked exhaust manifold. Though I occasionally hit 25+mpgs with mine as cracked as it was. I averaged 16-17

Guntar13

Keep the responses coming tons of good info!

Cruiser: When you say the relays on the passenger side, are you talking replace them? or just take them out, clean, dielectric grease them, then re-install?

Turbo: Although your post is factual and spot on, the solution "If your hurting now you may want to look at another type of vehicle", i don't agree with on the fact that it isn't really a solution. I thoroughly enjoy my XJ and it is in great shape for its year, just a couple "quirks", but nothing I can't get worked out. I don't think that obtaining another vehicle would be the best way to solve this particular problem.

So far the consensus is at the least replace the 02 sensor, so that is where i will head next, while I'm at it thoroughly check the exhaust manifold for cracks, any place that they "commonly" crack?
Thanks again everyone and keep em coming, oh yeah the map sensor van line is good, checked it while I was cleaning the throttle body.

cruiser54

Take 'em out, clean and reinstall. Not a bad idea to replace the O2 sensor.

DFlintstone

I see you are getten lots here! I had to chime in. That little tube there^CRUCIAL!.^ It's fragile and the slightest crack or leak, (or plugged), can HAMMER your mileage. Your MAP will tell your ECU to to tell your injectors you have your foot in it if it's not getting good vacuum.

Your 02 won't be able handle the "final touches" if a ton or fuel is being dumped in there.

I see 17 to 19 on my stock 90 (264K!), normal driving. I get a whole lot less doing short trips, firewood, trailer stuff. Going backwards.

Interesting info here on Renix O2's. http://www.naxja.org/forum/showthrea...ht=sensor+test

If you hear any hissing, including under the dash, that will lower your vacuum.

Guntar13

*Bump*,

I just love the ideas!

hankthetank

on my 90 i went from 10mpg to 17.5mpg by doing the following (chronological order):
battery,air filter, cap, rotor, wires, plugs (coppers), no cat (sorry just being honest), fuel filter, ford yellows (19lbs), contact/terminal cleaning, new battery and firewall ground, full intake manifold and TB clean, exhaust manifold repair (still not leaking, knock on wood), egr delete, full vacuum line refresh (made a big difference in my idle), sythetic 75w90 front and back, synchromesh in the ax.

most noticeable improvements are in red

Things i have not done and wont do until i notice a signifigant drop in mpg: o2sensor tps adjustment

i also use a good synthetic oil, gasoline with no ethanol ($$when i can find it$$), change my air filter more than i probably need to, never use anything fram (personal preference), grease everything regularly, check tire pressures weekly ( keep 'em a little bit high...) and i dont bag on my jeep. only once in a while do i give it hell, just to make sure it pulls smooth to redline. if it doesnt, then i start some investigating...

i also dont carry anything unless im absolutley sure i might need it.

some of this may not work for you, but i hope this helps a bit!

GA_Cherokee

lol i just spend 50 bucks on a new o2 sensor on a hunch. hopefully its gonna help my emission problem tho. good luck with yours