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Discussion Starter · #1 ·
Started keeping an eye again on mileage now that fuel has gotten so expensive.

When I first bought my FJ I was getting about 17.5 on average.
I have checked my mileage on the past 4 tanks and the highest I have got is 14.9 mpg (240 miles on a tank) and the lowest was 13.3.

Mechanically the FJ runs like new.
I've checked the air filter. Balanced and rotated the tires. Changed fluids. All regularly.

The only thing I can think is that it is due to add ons.
Since I was getting 17.5 I have added demello sliders, all pro pro links, ricochet skids and a few more lights.

Surely that stuff doesn't weigh enough to cut my mpg by 3-4?

Perhaps I need to get a tune up and get the plugs changed? I'm pushing 60K and I don't know if the previous owner ever did it.

Suggestions?
 

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fka luvshisfj
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plugs need to be changed about every 30k.....it would probably help out if you did change them
 

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fka luvshisfj
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One way you can tell if they've never been changed.....One side will be NGK and the other side will be Denso....(if I remember right)
 

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Just curious as to why plugs in some cars last longer and others not. My x-wives Northstar cady motor has no tune ups for the first 100,000 miles just oil changes.

Its got to something with a 4mpg loss I doubt its the extra weight unless you do big steal bumpers.
 

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Between the skids and light it could be enough to change your MPG's. I've also noticed that keeping the FJ clean and clutter free inside seems to help.
 

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I would love to know a solution to this as well, I only get around 250 km, so 155 miles to a tank.
My drive in the morning is short so me engine never fully warms up but its getting ridiculous.
 

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I would love to know a solution to this as well, I only get around 250 km, so 155 miles to a tank.
My drive in the morning is short so me engine never fully warms up but its getting ridiculous.
---------------------
07 FJ - Black Diamond
3' lift
285/17R70 wrangler duratrac's
Maybe it's the 3 ft. lift (I assume you have a 3" lift, but couldn't resist) that is killing your gas mileage?....:bigthumb:

KyFJGuy
 

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Discussion Starter · #10 ·
One way you can tell if they've never been changed.....One side will be NGK and the other side will be Denso....(if I remember right)
Changed them out today, they only said Denso and they looked pretty good so I assume they have been done before. Changed them anyway though.

Also, I found that the throttle body and MAF were both filthy.
In fact, there is mud residue inside the air box past both filters. There was mud on the MAF and Residue in the opening of the throttle body as well.
Seems strange as I have only been in mud 1 time in 8 months and I don't think I splashed around enough to suck mud and water into the engine.

Furthermore, the flame arrestor filter that is permanently mounted to the airbox is extremely dirty looking. Almost black. I can only assume after seeing mud residue behind it that it needs to be replaced but I am afraid to hack up the airbox while the vehicle is under warranty.

I'm going to monitor mileage now that I've changed the plugs, cleaned the MAF and throttle body. I can already notice better throttle response and the thing feels more peppy when I floor it.
 

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Discussion Starter · #11 ·
Well, just did a my first check since doing all of this work and what do you know? 17 MPG on the nose.
Unfortunately that was 99.9% interstate driving @ 70mph but it beats the hell out of 13mpg.

Looks like I may have fixed something.
 

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X2 on the t-stat. Itt looks like you fixed a lot of the noticeable problems. Glad to see you got it at least back whereit was. I was getting @ the same mpg (17-19) and found that thread about the t-stat and changed mine out even though there was no indication of it going out. Npg improved to @22-24. If you think about it , it'lll pay for itself iafter the7th fill up. Hope you success
 

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Discussion Starter · #13 ·
X2 on the t-stat. Itt looks like you fixed a lot of the noticeable problems. Glad to see you got it at least back whereit was. I was getting @ the same mpg (17-19) and found that thread about the t-stat and changed mine out even though there was no indication of it going out. Npg improved to @22-24. If you think about it , it'lll pay for itself iafter the7th fill up. Hope you success
Yea, I'm thinking about going ahead and doing it just to be sure. It's not like it costs alot.
 

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I had a similar experience this year with my '07. Change the plugs and air filter but it was still terrible. Then I cleaned the MAF sensor and everything went back to normal. I gained a good 25%. I also plan on doing the thermostat. I change it every 2 years. As they get old the spring gets weaker and may not close completely. This lengthens the warm up time and might even prevent it from reaching normal temperature on cold days so the engine just keeps running rich.
 

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Also, I found that the throttle body and MAF were both filthy.
In fact, there is mud residue inside the air box past both filters. There was mud on the MAF and Residue in the opening of the throttle body as well.
Seems strange as I have only been in mud 1 time in 8 months and I don't think I splashed around enough to suck mud and water into the engine.
By far your greatest concern should be the "mud debris" you found in your intake system, downstream of the air filter. Any mud or dust being injested by the engine is very bad news, leading to serious wear problems with pistons, piston rings, cylinder liners, valve stems, valve guides, etc. The intake plumbing behind the filter should be surgically clean. Are you using an aftermarket air filter, or the OEM paper element?

I'd check carefully for any cracks or holes anywhere in the air filter box or in the ducting between filter box and throttle body.
 

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well between yesterday and today my mileage went to shyt, was getting a solid 17-18 average even with 35`s, yeah I drive like a granny...

the scan gauge has been showing 11-12mpg`s, even if you figure out the math for the tire height change, it still isn`t good...

nothing changed but fuel!

added Startron enzyme additive to the past 2 tanks with premium fuel to make sure there wasn`t any water from past ethanol use...

the truck runs great and accelerates like a screaming monkey, with everything else being good, it has to be the fuel. Didn`t think they switched to winter blend so soon here in NC...

hmmmmm...
 
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