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Gas Milege Fix

A

aplatz

NAXJA Forum User
Location
Frederick, MD.
I've got a '96 Classic, 4.0, AW-4 w/ 117k. I've been keeping track of my gas miledge and recently switched back from 30x9.5 General Grabber ST's to 235 BFG AT's. My miledge seemed to get worse. I didn't change my speedo gear ever. I've changed my fuel filter. I am the only owner, and have changed my fluids ritually. I have no blow-by or lack of power etc. I used to get 250-275 miles per tank, now I'm 200-220 per tank.

Is my oxygen sensor the culprit? Gas gauge faulty? My plugs and distributor are fairly new too. What gives?
 
I'd start with the O2 sensor and the EGR circuit. Either could easily have an adverse affect on mileage.
 
Your 30s were nearly 10% larger than the 225's that are stock so-- as you decrease your tire size ,YMMV because you are going 10% further with the bigger tires. Example My Toy had 31's and when I went a measured mile on the freeway it would read 9/10 on the odo. When I put my 235's on for winter It read 1mile dead on. If I calculated my mpg with both I always got better with bigger tires but once I adjusted my figures for the tire difference it was nearly equal. Note, MPG in the winter also. cooler air = more hp=less mpg. HTH.
as always--YMMV
 
[ok... my half asleep brain tells me that Asat you must have missed the direction he went with tires.. he took bigger of and put smaller on so in theory he should have gotten better mileage.... but...
1. not all 30" tires are 30"
2. not all 235's are 29" (and change)
You have to check manufacturer spec heights....
Also tire pressure does a lot of you. Thread type and tire width impacts the mileage. Also I dump into my tank now about once a month some feul injector cleaner which brings me back up :D

Btw, also when is the last time you cleand your TB? How are your oxygen sensors? is your cat maybe plugged ?? A lot of things can cause reduction in mpg and they just might happen to conicide with something else, or you might just notice them since you just did something that prompted you to pay attention to it...
 
Yeah, I've always been a sucker for the "snake oil products". Wether it's injector cleaner or Engine Restore stuff you put in w/ fresh oil. I can't tell the difference, but I do it anyway.

Please explain the EGR circuit? EGR Valve I've heard of (and haven't changed yet)

As far as my throddle body, I just checked my air box and tube. Not even dust showing. Didn't think cleaning that would be needed. Just spray carb cleaner around? Just unbolt, w/ no adjustments needed?

What's part cost looking like?

1-Ox Senson-$60?
2-EGR???
3-Cat will HAVE to wait (leaving job, moving, looking for a house in N.VA)

PLATZIE
 
well couple things... cleaning tbody is best done with the tbody off the vehicle....

the cat can be tested for being plugged by a hand in a glove temp check (search for cat in oem... it was discussed a while ago.. don't remember the details though)

getting back to tbody... just remember what goes on back were and you're good :D
 
EGR is spendy. I couldn't find an after-market so a trip to the stealership cost me about 150. Word to the wise. DON'T TOUCH THE EGR UNTIL YOU KNOW FOR ABSOLUTE CERTAIN THAT THE CAT IS OKAY!!!!!. If it's plugged expect to buy another expensive EGR upon first engine start.

I cooked my shiney new EGR because the morons at Midas convinced me that my cat was okay even though I told them to replace it (I guess that makes me a moron too for believing those monkeys). :(
 
there is no egr on a 96, only on the renix 1987 - 90. you can clean the TB with it still on the engine if you use throttle body cleaner, although the prefered and more thorough method is to take it off.

i always get worse mileage in the winter months and good mileage in the dead of summer. because cold air is more dense than warm air, more air is being sucked in to the intake which will require more gas.
 
89xj said:

i always get worse mileage in the winter months and good mileage in the dead of summer. because cold air is more dense than warm air, more air is being sucked in to the intake which will require more gas.
Click to expand...


Additives in winter gas give worse mileage too.
 
Has anyone thought of just tires spinning or letting your vehicle warm up in the cold as to why he would get worse milage. By the way how much do you lose? My 91 warms up for 15 min every am before work and I only get 18mph. In the summer I am at 20-22.
 
In California they reformulate their gas to better emmisions occasionally. I seem to get worse milage everytime they do it.

When my Jeep was new I used to get about 270-280 miles per "full" tank fill-up. Now I get about 230-250. I think some of it is the gas. The main culprit for me is traffic. I drive the same route and distance as when it was new, BUT I used to be able to drive at freeway speeds. Now it is very rare that I am not in stop and go traffic followed by stop and slow. I long for that impressive "Highway Mileage' figure people talk about.

Just something to consider.
 
During the winter months they “oxygenate” the gas, at least up here in AK. I’m not sure what it does or if it affects gas mileage, but it does a good job of clogging up weed eater and lawn mower engines :(

Terry
 
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