Gas Mileage question

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Feb 17, 2011
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I am only getting 175 miles per tank before my gas light comes on. I have 265 75 16 bfg. Is this normal? I am pretty sure I was getting a lot more than that before I put the BFG on. I was prepared for it to make a difference but not this much. It is not bothering me enough to make me want to sell it but if there is something that I need to do or am not doing please advise. I drive an 02'
 
Welcome to the Mud!

How long have you owned the cruiser and what kind of maintenance history does it have? I agree that something seems off. You shouldn't be getting such low mileage with tires that small, even if they are BFGs. First and foremost, what is your driving style like? I have found that romping on these rigs will eat tons of fuel, so if you drive aggressively you'll see very poor mileage.

On the maintenance side, I would start with the simple stuff first. How is the air pressure in the tires? How does the air filter look? What kind of gas are you running and which octane are you using?

From there I'd check the MAF sensor. I've found that even if it looks clean, there could be an invisible film of dust/crud on it. Buy some MAF sensor spray cleaner and spray it off. Do not touch anything to the wires or try to physically wipe them off. Just spray the cleaner onto the sensor wires, let it dry thoroughly, and re-install. I pciked up about 1-1.5mpg after cleaning mine. I'd also check for intake/vacuum leaks while your in there. Is the truck running ok? The more information you provide, the easier it is for us to make recommendations.
 
I do not drive aggressive at all. I am also not very well educated in the mechanic field so please excuse my ignorance. I am due an oil change so I am going to start there and get them to replace my air filter. It runs fine and I use 91 octane. Is it easy for me to check my MAF sensor? Thanks for your response and advise.
 
Yes it is, basic hand tools are all that is required. Check the link that Pfran posted above for more info.
 
Winter I get 225-270 and I never let the gas light come on...Summer, 250 - 325 miles. Very unscientific, depends on a lot of factors.

I just cleaned my MAF and Throttle Body...use the "search" - both are very easy/simple.
 
I can average about 300 if I drive very, very conservatively. I usually get about 250 though. Mine is not stock, and still gets about 17mpg on highway.
 
You've either got an extremely dirty MAF or you have between 120K and 140K miles on your truck and you're less than 1000 miles from throwing a Check Engine Light for a faulty front O2 sensor. The MPGs drop WAY off before they go out completely and trigger the CEL. Read up on Denso replacements. $60 on Amazon instead of $160 @ the dealer.
 
My air filter was clean. I called a local mechanic who works on Toyotas and he said that if the O2 sensor is needing to be replaced my CEL would have come on. Is this always true? I have looked at the instructions on cleaning the MAF and I honestly do not feel comfortable doing that myself. How much does it usually cost for a mechanic to do it? Thanks again for everyones advise.
 
Just give it a little time. The CEL is coming if it's the O2 sensor.
 
My air filter was clean. I called a local mechanic who works on Toyotas and he said that if the O2 sensor is needing to be replaced my CEL would have come on. Is this always true? I have looked at the instructions on cleaning the MAF and I honestly do not feel comfortable doing that myself. How much does it usually cost for a mechanic to do it? Thanks again for everyones advise.

It's a 5 minute job plus a half a can of CRC MAF cleaner from Napa. My :princess: could do it - don't be intimated by it being an electronic part. The MAF comes out of the intake just south of the filter. With the engine off and key out, disconnect the harness. Pull the screws, it comes out vertically upward. Place a cloth under it to collect the drips. Spray down the three wires. Keep in in roughly the same vertical orientation so that the drips run down and not up toward the head. Let it dry thoroughly. Replace and :steer: happy!
 
it's a 5 minute job plus a half a can of crc maf cleaner from napa. My :princess: Could do it - don't be intimated by it being an electronic part. The maf comes out of the intake just south of the filter. With the engine off and key out, disconnect the harness. Pull the screws, it comes out vertically upward. Place a cloth under it to collect the drips. Spray down the three wires. Keep in in roughly the same vertical orientation so that the drips run down and not up toward the head. Let it dry thoroughly. Replace and :steer: Happy!

Remember: Do not touch the wires on the MAF!!!
 
... he said that if the O2 sensor is needing to be replaced my CEL would have come on. Is this always true? ...

Just to reiterate what I said...

bamachem said:
The MPGs drop WAY off BEFORE they go out completely and trigger the CEL.
 
Sippi, I'd like to reiterate how simple it is to clean the MAF yourself. However, if you truly aren't comfortable doing it, theres no shame in taking it to a shop that can do it for you. They will charge you much more than you'd pay doing it yourself, probably in the neighborhood of $50 for a 5-10 minute job, but that is much better than doing something you aren't comfortable with and risking damage to the MAF.

This thread has got me wondering about my 02 sensors since my mileage sucks despite my driving like grampa jones. I'm right on the high side of the mileage range at 136K. Might be time to peruse Amazon...
 
I'm telling you guys... On a Toyota Truck, if you have a sharp mileage economy decrease after 120K, it's *most likely* an O2 sensor that's on it's way out, but isn't so far out of spec to trigger a CEL. Kind of like when the MAF or Throttle Body gets dirty, but not dirty enough to trigger the CEL... Same principle applies. There's a RANGE to the specified performance which is reported to the computer as a control signal, and as long as it's in that expected range, whether wrong or not, then the computer won't know any different. Also, the O2 will be OK for a while, then one or two tanks you might drop 20% or more on MPG's, then it might jump back up or stay where it's at. They're funny like that. When a MAF or TB gets dirty and loses performance, you don't see a dramatic drop, but one that slowly degrades over time.

I've had THREE toyota SUV's do the same thing, and almost identical mileage. This has been my experience over the last 7-8 years and others report similar things. I'm just offering my observations to help you pinpoint the issue.

The moral of this story is "don't overlook checking the O2 sensors with a multimeter just because you don't have a CEL".

As a front O2 sensor is on it's way out, the control signal will not be where it should. The engine will base the fuel mixture on the feedback it gets from the O2 and the amount of air it senses across the MAF. The throttle body is what controls the amount of air allowed into the engine. That's why these things are so critical in fuel economy. The computer uses the O2 sensor to adjust the fuel mixture so that there's a small bit of oxygen and unburned fuel exiting the cylinders to get a secondary "burn" in the catalytic converter and reduce the NOX emmissions. When the signal begins to go out, it doesn't sense the unburned fuel as well as it should, and the computer thinks the engine is running lean, enriching the mix. When this happens, you consume more fuel than you should, and you might even be able to smell it in the exhaust if it's REALLY out of spec. The thing that eventually triggers the CEL is usually when the heater circuit (for start-ups) goes out on the MAF, and not a faulty signal.

Posted this @ 10/27/2009:

116k miles.

(6) qts Royal Purple 5W30
(1) Mobile 1 M1-109 Filter
(8) Denso Platinum+ Plugs
(4) qts Synthetic ATF (drain and refill pan)
(1.6) qts Royal Purple 75W90 in front diff
(1.4) qts Royal Purple 75W90 in transfer case
(3.4) qts Royal Purple 75W90 in rear diff
Greased zirks in driveshafts

Cleaned Air Filter, MAF, and Throttle Body

Checked air pressure in tires (38 PSIG all around)

Besides laying off the skinny pedal, anything else that I'm missing for fuel economy???

I'm hanging at around 13MPG when it used to get around 16-ish in mixed conditions. I'm thinking I may have an O2 sensor on the way out. Similar thing happened on a 4Runner I had, and changing the front O2 sensor put the mileage back where it belonged.

Do the O2 sensors "fade" when they are on thier way out on the UZJ's?

In April 2010, I got a CEL:

I got a pair of front DENSO oxygen sensors off of Amazon.

They were $53 and change each, then I signed up for some deal where they gave me 2-day air for free. All you have to do is then "opt-out" of the renewal and the shipping becomes completely free and they don't charge you for the service.

Anyway, for $106 shipped via 2nd day for the pair was just too good to pass on. I've had a CEL for Bank 2 Sensor 1 for about 6 weeks now and I'm just now getting around to getting it taken care of.

There hasn't been any appreciable change in the "average" mileage, but occasionally, I'll have a "bad" tank where I'll get 13MPG or so compared to the normal 15-16MPG (300 miles before the idiot light comes on).

I swapped them out in my garage in all of about 20-min for the pair. These are OEM @ 128K, and the truck has zero rust (10-years in the south).
 
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Makes sense to me, and funnily enough I have commented to my wife twice now about how rich the exhaust smells. Would extra unburned fuel screw up emissions though? Because my cruiser passed with flying colors...but the fuel smell in the exhaust is undeniable. Off to Amazon I go. $106 wont kill me even if it doesn't completely solve the issue. It'll be good to replace them anyway.
 
Bamachem - Do you have a link to those sensors on Amazon? 135k miles and just got a CEL this morning. I'm suspecting O2 sensor. The right side was replaced 20k miles ago, so probably the other one.
 
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Bamachem - Do you have a link to those sensors on Amazon? 135k miles and just got a CEL this morning. I'm suspecting O2 sensor. The right side was replaced 20k miles ago, so probably the other one.


I just installed 2 pre-cat O2 sensors in mine this weekend. I bought them from Amazon. Below is the part number I used. They were 55.46 each.

2 Denso 234-4169 Oxygen Sensor (Air and Fuel Ratio Sensor)"
Automotive; $55.46
 
Thanks, smm3. I believe a 22mm box wrench is all I needed, correct? (maybe some liquid wrench, too). I'm praying that the old sensor will come out easy.

BTW, did you end up accessing the sensor through the wheel well?
 

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