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Discussion Starter · #1 ·
Bought this 2008 X 2 weeks ago, I know they are not the best for efficiency but 8-9 MPG is quite shocking. My 2003 gets 14 to 16....
The skinny, it's a 4.0, 4X4 with 202000+ on it. The engine, tranny and everything about it looks mint, not a drop of oil of any kind... Changed plugs, air filter, cleaned MAS, cleaned throttle body. Found out the fuel filter is in the tank, fine place to put a filter so have not gone there yet, another thread. What else can I look at to figure why the MPG sucks. I've researched and came up with timing. How do you check the timing, there is no plug wires to hook up the induction light, this is new to me.
 

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Bought this 2008 X 2 weeks ago, I know they are not the best for efficiency but 8-9 MPG is quite shocking. My 2003 gets 14 to 16....
The skinny, it's a 4.0, 4X4 with 202000+ on it. The engine, tranny and everything about it looks mint, not a drop of oil of any kind... Changed plugs, air filter, cleaned MAS, cleaned throttle body. Found out the fuel filter is in the tank, fine place to put a filter so have not gone there yet, another thread. What else can I look at to figure why the MPG sucks. I've researched and came up with timing. How do you check the timing, there is no plug wires to hook up the induction light, this is new to me.
This is the perfect place to have a scanner that reads out your run data in real time. Are all your air intake hose clamps good and tight from the air box back to the throttle body?
 

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Are you running extra large tires?
Taller tires will be the equivalent of having a higher gear ratio, which will give you crappy MPG, especially in the city.
I have a 2004 4x4 and the stock tires are P265/65R17.
I am currently running LT265/70R17, which are just a little over 1 inch taller than stock.
I am currently getting roughly 20 MPG city and around 22 MPG highway.

If your Xterra is in good condition and tuned up properly, then see what size tires you have.
If they are those big balloon off-road tires that might be part of the problem.
Also check your tire pressure. If the pressure is too low that will also make the engine work harder than it should.
 

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Discussion Starter · #5 ·
Are you running extra large tires?
Taller tires will be the equivalent of having a higher gear ratio, which will give you crappy MPG, especially in the city.
I have a 2004 4x4 and the stock tires are P265/65R17.
I am currently running LT265/70R17, which are just a little over 1 inch taller than stock.
I am currently getting roughly 20 MPG city and around 22 MPG highway.

If your Xterra is in good condition and tuned up properly, then see what size tires you have.
If they are those big balloon off-road tires that might be part of the problem.
Also check your tire pressure. If the pressure is too low that will also make the engine work harder than it should.
I have 16" on them and inflated correctly. May have to bring to a shop and have them hook it up to an analyzer see if there are any issues I can't see...
 

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I have 16" on them and inflated correctly. May have to bring to a shop and have them hook it up to an analyzer see if there are any issues I can't see...
Yeah, if you've eliminated the most common and obvious things that impact MPG then you'll have to have the PCM checked. A fault in the computer system could be making it go into "limp mode" which is nowhere near the efficiency it's capable of.
 

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Discussion Starter · #7 ·
Yeah, if you've eliminated the most common and obvious things that impact MPG then you'll have to have the PCM checked. A fault in the computer system could be making it go into "limp mode" which is nowhere near the efficiency it's capable of.
wouldn't limp mode make it run not so good?? the X runs great thats what I cannot understand... Is there a way to test the coil packs?? I replaced the plugs and the old ones were not fouled at all, they all looked the same.
 

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wouldn't limp mode make it run not so good?? the X runs great thats what I cannot understand... Is there a way to test the coil packs?? I replaced the plugs and the old ones were not fouled at all, they all looked the same.
Is this 8-9 mpg your calculation or a digital dash readout for mpg?
 

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wouldn't limp mode make it run not so good?? the X runs great thats what I cannot understand... Is there a way to test the coil packs?? I replaced the plugs and the old ones were not fouled at all, they all looked the same.
I'm only speculating based on your reported MPG.
Limp Mode does not necessarily mean it will run bad.
It just means it is in a safe mode to prevent things like pinging or knocking.
It also means that the air fuel mixture will be set to a factory default so that it can run good enough to get you home or to a shop.
From what I've read the main symptoms of limp mode are poor mileage and poor performance.
But it is also accompanied by a "Service Engine" light. So if that light is not on then it could be something else I am not familiar with.
 

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I think vacuum leaks would trigger the "Service Engine" light.
But a stuck fan clutch would consume a significant amount of engine power. That would be easy to check. With the engine off try to rotate the fan by hand. If it moves freely then the clutch is good.
I think that dragging brakes or bad wheel bearings would produce some noticeable noises.
When my dad's brakes wore out there was a rattling sound from the rotors.
 

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good question, it is both. I calculated at my last fill up before I knew it had a dash readout. I was amazed it did have one..
FYI...when you have the digital dash in the "mpg" mode you can push and hold the push pin selector for 5 secs or so and it will reset and give you a fresh reading.
 

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Discussion Starter · #15 ·
I'm kinda broke down right now as far as running the X, need to get new headlights, they should be here monday. In the mean time I may drive to the local shop and have them put it on an analyzer. Probably money well spent to see where things are at.... I'll update when done..
 

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I'm kinda broke down right now as far as running the X, need to get new headlights, they should be here monday. In the mean time I may drive to the local shop and have them put it on an analyzer. Probably money well spent to see where things are at.... I'll update when done..
If they say it's the Defibrillator or kanutter valve. Walk away!
 
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