Serious Drop in 4RNR fuel economy

[Applejack]

About a month ago I took a trip up north to visit my brother.
It was all freeway driving, and I would guesstimate that I was averaging 68mph.
On the way there I only averaged 14.2 mpg! I would normally have gotten at least 20. I chocked it up to some bad gas but on the way back it wasn't much better, with new gas at a different station I averaged 14.8. I've run through a couple of tanks since and changed my air filter. With combined city/highway driving it's sticking around the 13.5-14 zone. Normally I would get 16-17 in town driving. Not sure where to go from here, any suggestions?
I haven't changed the plugs since I bought it a year ago, but I'm not thinking that's the problem. This was not a gradual decline in mileage, this was a steep descent. Other than that she is purring like a kitten..........a very hungry kitten.

 

[mtnbike28]

Not that bad but...

I get a decent drop each winter when they change the gas mixtures.... but yours seems greater than my average. I will be watching to see what is said.
(ps do you have a scan gauge? If not, if somebody does, is there a reading that can help diagnose the problem?)

 

[OldSven]

Any "mods" (tires, gears, weight) since you got that 16mpg average? Mine with stock gears, 255's, and all my junk was getting about the 13-14 mark also. Now with 265's and capping the deckplate for good I'm seeing some higher miles but I haven't ran a full tank yet but so far looking better.

 

[CYi5]

Change out your fuel filter. It's like $20 for a good napa gold one. Located on the inside of the driver's frame rail.

 

[Applejack]

"I get a decent drop each winter when they change the gas mixtures."

Here in Oregon we have a 10% ethanol mix all year round.

I have added and ARB bar but that was after the drop in mpg. Other than that nothing had changed. I forgot to mention that I changed the diff and t-case fluids, which did nothing to help, but I figured as much.
I was thinking about taking it in the have the injectors cleaned, but I don't want to spend the $$ if that wouldn't do much. The key to efficiency in FI's engines is atomization of the fuel, and I thought that perhaps the injectors are having some issues there.

 

[Applejack]

Change out your fuel filter. It's like $20 for a good napa gold one. Located on the inside of the driver's frame rail.

I guess that might be a good and cheap thing to try, before going in for an injector service.

 

[OldSven]

When I got mine I ran it over to Jiffy Lube (I know:elkgrin and had the injector machine hooked up and the runner sat there smoking like a mac truck for about 15min a few good rev's later and she was all cleaned out...

 

[Dave Bennett]

Any engine codes? O2 sensor, MAF, CAT all good???

 

[Applejack]

Any engine codes? O2 sensor, MAF, CAT all good???

No codes, so as far as I know it's all in good working order.

 

[Dave Bennett]

Spark plugs new and gapped correctly?

 

[keezer37]

Before you clean the injectors, run Chevron/Techron fuel system cleaner through. Do it a couple times. I'm not a believer in additives but this does work.
It is butane that they add to the winter mix of gasoline but I would think you should have noticed this earlier in the year. Then again, I'm sure winter mix times are regional.
Here in Ohio, my gas mileage drops a bit more than 15% in the winter. This happens in November for me.

 

[corax]

try putting 3 oz acetone per 10 gallons gas for a few tanks. Supposedly acetone is supposed to increase fuel economy by reducing surface tension thus aiding in vaporization. I don't know if that's true, but I do think it will help clean varnish off the injector tip. A few years ago I did this for a month straight on the 7MGE in my 4runner with no ill effects (can't remember if I gained MPG). I've also read an independent study where someone measured a bunch of fuel system o-rings and put them in straight acetone for a month, there was no noticeable deterioration or change in dimension (no swelling, etc).

 

[Goin]

I feel your pain. I have a 2001 4runner with 285/75/16, roof rack, and a fair amount of armor. I too saw a large drop in mpg this fall, before I was seeing 15 to 18mpg depending on the drive. Now I am getting high 12 to low 14s regardless of city/hwy driving (equiped the same and really trying to go easy on the accelorator). That is rediculous for a 4runner. I should have gotten a landcruiser. At least my range would be better with the larger gas tank. I am filling up after just over 200 miles and am contemplating aux tanks. I searched on the subject and chalked it up to the winter gas, but am not happy. Geez. Rant off!

If there are more maintance type suggestions for increasing mpg. I am all ears. Thanks.

 

[Cackalak Han]

My brother's 4Runner had an O2 sensor go out and the drop in MPG was similar to yours. I believe you can get an OEM unit for ~$80 and it's simple to switch out (unless it's super rusted). But if it were me, I'd do the fuel filter and spark plugs first.

 

[Howard70]

Mass Flow Air Sensor?

We had low mileage on our first generation 4runner that turned out to be due to a tired mass flow air sensor (not sure if that's exactly the correct term or not). Replaced it and mileage went back to the low 20's (22re).

Howard L. Snell