Horrible MPG

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Apex

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Hello all,

Currently getting 11-12 mpg average per tank for the past few months or so. I've tried a number of things to try to fix the issue.

- I Recently did plugs, NGK coppers. New PCV. Swapped two coil packs.
- New IAC valve
- cleaned throttle body
- pulled vaccuum lines off my parts '04 and swapped them over so they're not new, my old lines were cracked at the "T" before it reaches my air intake tube so I just wanted to fix the leak. No vaccuum leaks detected.
- Intake filter recently washed/oiled
- New water pump and thermostat, all new Zerex and distilled water (old factory WP pilot bearing finally gone at 255k mi, started leaking)
- Tire pressure is good
- I seafoam the gas tank twice a month, so I don't think faulty injectors
- Checked all brakes, even adjusted parking brake, none are sticking

I'm leaning towards fuel pump/filter, or transmission. Maybe even both. I'm almost to 260,000 mi and fuel pump and trans are original. I've been hearing a distinct "burping" sound coming from rear driver wheel well after the KJ has been driven and turned off. Vibrations and jarring, such as closing one of my doors, will sometimes cause it as well. There are no running issues though. No check engine light. Idling at 600 rpm after warm up. Plenty of power for an out of ratio setup and an older engine. Oil and filter get changed religiously at 2,500 mi, full synthetic, leaks a quart between changes and doesn't burn much.

On a side note, there is a residue on the inside of my rear passenger brake rotor dust shield, maybe axle seals going bad? Doesn't seem like that would drop MPG though.....

Waiting on ATF to do trans filter/oil, and while I'm at it, going to do transfer case and 8.25 as well. Been awhile lol

Some background vehicle specifics, I'm running 265/75/16 with 3:73s, was getting much better mileage than this the past few years, 18 mpg highway.
 

HoosierJeeper

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Is that in town? Honestly, given your mods, that sounds about right if it's cold and you're doing lots of idling and all in down driving. I'm at 13mpg 100% stop and go, mostly short trips. If that's highway, that's bad but in town that's probably about normal.

That residue, if it's not wet/drippy I wouldn't worry. It's just dirt and grime probably.
 

Apex

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I let it warm up a few minutes in the morning and then I go. Same in the evening after I'm off work. I have a short commute to work but it's all highway at 60 mph. When I take trips to town I reset the EVIC after I get going to see what I'm getting. It'll get up to around 15 or so but I don't trust it completely. Miles to empty drop at an erratic rate. Most recently my average plateaued at 11.8 though, which is what the MPG calculation gave me.

Bottom line is though, I'm getting around 200 miles per tank before the light comes on, my wallet is feeling it and it just doesn't seem normal.
 

tjkj2002

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I'm almost to 260,000 mi

I'm running 265/75/16 with 3:73s

Problems found.

Your trans is super confused since your running 265/75's on stock gears,those tires alone account for at least 8mpg highway loss and 261k on the clock everything is just worn out.

You can not hand calculate or trust any evic reading for mpg's because of the gearing and tires.Your traveling much father then your ODO is actually reading.
 

Apex

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You can not hand calculate or trust any evic reading for mpg's because of the gearing and tires.Your traveling much father then your ODO is actually reading.

Hmm, good to know. I'm guessing downloading an app with a GPS mileage tracker will give me a much more accurate reading with the calculation.

I had the speedo calibrated, but apparently that does nothing for the odometer. Regearing will fix this as well?
 

tjkj2002

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Hmm, good to know. I'm guessing downloading an app with a GPS mileage tracker will give me a much more accurate reading with the calculation.

I had the speedo calibrated, but apparently that does nothing for the odometer. Regearing will fix this as well?

They got close,I know I did the same thing.Re-gearing to 4.10's will give a increase in mpg's but your still going to be low due to the fact 265/75's are 20-30lbs heavier each then stock.
 

towpro

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If changing to 4:10 is going to raise the MPG, why can't one just drive around (not highway speeds) with OD turned off and save fuel? It sure seems to run better on 45mph roads with OD turned off.
 
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Myke

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If changing to 4:10 is going to raise the MPG, why can't one just drive around (not highway speeds) with OD turned off and save fuel? It sure seems to run better on 45mph roads with OD turned off.
Gears in your diff vs gears in your trans changes where the load point is and that has an affect. Also OD off doesn't affect 1st or 2nd gear loads where it takes the most energy to get the vehicle moving.




Or this could all be a lie. I'm not an engineer.
 

renegade 04

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I lost a few mpg when I went to 4.10, but then again I still have stock sized tires. Much better to drive and also way more fun as well. I would recommend that you change to 4.10 or really 4.55 if you want power. And at the same time you should replace all the bearings and seals in both the front and rear differentials.
 

tjkj2002

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Gears in your diff vs gears in your trans changes where the load point is and that has an affect. Also OD off doesn't affect 1st or 2nd gear loads where it takes the most energy to get the vehicle moving.




Or this could all be a lie. I'm not an engineer.

Locking out OD only does just that.......prevents the trans from shifting into OD.Has nothing to do with the gears in the trans or the diffs.
 

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