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Huge MPG drop!

slapshot said:
just a heads up, if you are calculating your mpg solely from your gps readings you will always be inaccurate. GPS is only accurate to 3 meters, i'm not going to convert that into yank units for you but approx 3 feet in a meter.

farmers who plot gps coordinates for combine purposed often approach their desired waypoint etc ( corner of property) from multiple directions (3-5) using gps they average the coordinates to get an accurate reading. this is very common when determining property lines.
even DARPA would agree with the general inaccuracies of gps.

If your speedo gear is stock, your odometer will be out, and if you are taking gps readings gospel, you have no chance in being accurate.

This being said i have no doubts that you have lost some mpg, but i would be willing to bet it isnt to the the degree you have stated . More like your value +/- 3 meters x distance traveled standard deviation
Click to expand...

Bah, basic GPS is pretty dang accurate for measuring distances. The basic WAAS correction you find in handheld GPS is generally accurate to within 20-feet for position if you have good satellite coverage at the time. Speed is usually better than 1% if you're holding a steady speed and straight course.

Surveyors and farmers do the time averaging because they want an accurate position. Absolute positional accuracy doesn't really matter for relative measurements like speed and distance. BTW, I get to play with the military GPS on occasion and using the full military setup with differential corrections and phase corrections is damn accurate.

Oh, I second the O2 sensor.
 
VAhasnoWAVES said:
i call shens...







flush your fluids. if that fails then run it hard, blow some of that carbon out. fuel injector cleaner doesnt get all of it.
Click to expand...
Call it all you want lol
I get a reading of about 250-260miles out of a tank and when corrected that comes out to be about 325 actual miles driven. Fill up with 18 gallons and im getting right at 18mpg.
 
Bobby@Bullydog said:
Call it all you want lol
I get a reading of about 250-260miles out of a tank and when corrected that comes out to be about 325 actual miles driven. Fill up with 18 gallons and im getting right at 18mpg.
Click to expand...

Is it all flatland or are there hills involved.

another suggestion that I didn't read in the thread, check to see if the engine is fully warming up. if the thermostat isn't working right, the engine wont run @ 190 degrees and never go into closed loop.
 
Bobby@Bullydog said:
Call it all you want lol
I get a reading of about 250-260miles out of a tank and when corrected that comes out to be about 325 actual miles driven. Fill up with 18 gallons and im getting right at 18mpg.
Click to expand...
are you doing these calculations yourself? sure, math is nothing but fact. even einstien proved the theory and eventually existance of black holes through mathmatical calculations. but that doesnt mean i trust them when it comes to an XJ.

get your speedo gear to the correct ration or use a GPS and come back with those results (over a multiple trial circumstance). though there could be something your not telling us... stroker? where are located, what is the climate like where your at, how is the terrain. or your could drive like a grandma... which is it?

dont take this as me bashing you, haha. hell, send me a PM with what you do for general maitnance on your XJ, id love to improve my gas milage. because im not getting a whole lot better than that with my stroker and slightly smaller than stock tires.
 
Since it appears as though you have checked all the recommendations as for ignition items, fluids, and speedometer calibration...
Have you checked to see if you have an exhaust leak or obstructed catalytic converter?

Recently I replaced the 1st generation Gale Banks header due to crack in the collector and was upgraded to their 2nd generation redesigned header....
With the lack of exhaust leak and redesigned tube routing I received more power and better MPG....

On a recent trip to Death Valley with the Jeeps cargo area loaded down and driving 70-80 mph; I received 15 mpg....
Thats up from 12-13 mpg....
 
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VAhasnoWAVES said:
are you doing these calculations yourself? sure, math is nothing but fact. even einstien proved the theory and eventually existance of black holes through mathmatical calculations. but that doesnt mean i trust them when it comes to an XJ.

get your speedo gear to the correct ration or use a GPS and come back with those results (over a multiple trial circumstance). though there could be something your not telling us... stroker? where are located, what is the climate like where your at, how is the terrain. or your could drive like a grandma... which is it?

dont take this as me bashing you, haha. hell, send me a PM with what you do for general maitnance on your XJ, id love to improve my gas milage. because im not getting a whole lot better than that with my stroker and slightly smaller than stock tires.
Click to expand...
I didnt do this with just simple math and adjust it due to the percentage of a larger tire.
But I dont drive this thing but to and from work every day. Its 47 miles there and 47 miles back no detours. Im able to go back and forth 3.5 times and still have 2 or 3 gallons left. SO...thats 329 actual miles before I fill up with 18 gallons. I think I know what my jeep gets as far as mileage :)

and as far as mods...its got a rigged cone filter and ford 19lb injectors..thats it.
 
see, this is where that doesnt make sense.

with 3.07s (ax15) and 31s thats about the same RPM range i see at that speed, and i get almost litterally the same milage on 31s. but logic says that a bigger heavier tier would make the motor work harder to turn 35s.

maybe your motor just runs strong or something. :dunno:
 
Alright well I have been able to put a few tanks of gas through my Jeep since my last posting when I replaced the TPS. No change still the same mileage, right around 14.5mpg. I see a few new ideas since that last posting as well. Fuel Filter - I have not replaced it recently no, however I did change it last year when I went through all the filters and fluids on the Jeep. As cheap as they are I guess it wouldn't be a bad thing to try although I never noticed a bad tank of gas. Exhaust - I had the stock header replaced about a year ago as well do to a large crack at the #5 cyl. I bought a Banks header directly from them and then had a local mechanic install it after I realized I had to pull the intake as well to swap it. Worth the money to avoid the extra grief. The rest of the system is stock and looks in good shape although I have not looked in the cat so I could have an issue there. Future plans include a new cat and full exhaust. Finally I used my GPS to test the accuracy of my speedometer. I use the vehicles trip odometer to figure my mileage. Just as I always have. The +/-3m variation wouldn't make that big of difference and even if it did as long as I am always using the same method, accuracy wouldn't matter so much, a drop in mpg would show up regardless. It will be a little while before I can test any of these last suggestions along with swapping O2 sensors since I am currently unemployed and funds are extremely lacking currently. thanks
 
My speedometer is accurate with my 30's as well, and the same was true with my last XJ. As for your mileage, I too vote for the O2 sensors.
 
Bobby@Bullydog said:
I dog it when i drive in town and when on the highway im cruising at about 70 @ 2100
Click to expand...

I don't see how you can be cruising 70 at 2100rpm with that combo. I think if you do the math, 70mph would be at a lot lower rpm (1800rpm is ballpark). 2100rpm is around what stock gears and 30" tires will run at that speed. As a guess, I would say that you would have to be doing over 80mph at that RPM and just haven't replaced your speedo-gear...in which case, you are going farther than is being indicated and therefore getting even better mileage. I just don't know...something just seems off. Maybe someone can plug your gears/tires into a calculator and post the results.
 
He also thought he had stock 3.07 gears on an auto 4.0... I suspect some or most of the numbers are off. Not saying it isn't possible to find 3.07s stock on an auto/4.0 combo, but I've never seen it and it'd have to be a special order at the dealer.

EDIT: unless it was originally a manual XJ and someone swapped it to auto at a later point in time.
 
Ok so it has 3:55s
But regardless with my GPS showing 70mph my speedometer reads 58mph.
I know how many miles I drive a day and how much I fill up with on fuel every 3 days.
17-18mpg..all day
 
I'm taking a very big interest in this thread. I just ran out of gas about a quarter of a mile from my house with 211.8 miles on a full tank. Much walking, creative language and sore arms from the carrying of the gas can ensued. I'm here searching for the elusive answer to this quandary.

I do have a question for the OP though: has your front end been making any noise lately? Bad U-joints and/or wheel hubs add a lot of rolling resistance. As far as I can tell, this is at least part of my problem at the moment. I'm ordering mine tonight!
 
To get the best mileage possible there are many factors.

1. Altitude(air pressure/O2 content)
2. Driving conditions( weather, hills, ect.)
3. Do you drive like Grandma or Dale Earnhart.
4. Condition of Motor/drivetrain(Fluids((synthetic))Tune, Mileage ect.)
5. Tire size w/proper gearing.
6. Correct alignment and Tire preassure.

You factor all these in and there is no reason you cannot get good gas milage! You must remember that driving a Cherokee is like driving a brick and you will never get great mileage! :patriot:
 
bullardsbarbarian said:
I'm taking a very big interest in this thread. I just ran out of gas about a quarter of a mile from my house with 211.8 miles on a full tank. Much walking, creative language and sore arms from the carrying of the gas can ensued. I'm here searching for the elusive answer to this quandary.

I do have a question for the OP though: has your front end been making any noise lately? Bad U-joints and/or wheel hubs add a lot of rolling resistance. As far as I can tell, this is at least part of my problem at the moment. I'm ordering mine tonight!
Click to expand...
This is why I now carry a 2.5 gallon jerry can in the back... but still, try to avoid running the tank dry, it damages the fuel pump seals.
 
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