So with all of the threads of poor mileage, I thought I would share a success story.

I purchased my 4runner a few years ago from a big city (St. Louis) that was 2 hours away from me by interstate. I remember filling up in the city, driving home, and filling up again to check the mileage. BONE STOCK 99 limited with cruise set on 65 I got 22 MPG highway. The vehicle soon started throwing a code, but it just turned out to be a sensor that needed cleaning (MAF I believe). Over the next year when I would check it, I would get 19-20 with a mixture of city/hwy driving.

Last spring I decided to add a small lift (1" spacers & new shocks)and I also put on the next size up tires (AT tires from Firestone). I also replaced the spark plugs with NKGs that several people on here recommended, and new air filter. I did all of this in preparation to go to Colorado last summer. Ever since I did these things, my mileage was never better than 18, and was usually 16.5-17.5.

Well, THIS spring I decided to see if I could improve the mileage. I replaced the fuel filter, and I pulled the spark plugs (less than 10K on them). Plugs looked fine. I replaced the plugs with the denso ones from Toyota. I also pulled the throttle body and cleaned the crap out of it with parts cleaner. I also replaced the diff fluids in the front and rear diffs and the TC with synthetic 75x90 (I think that is the weight).

Today I checked the milage after a full tank of gas: combined city/hwy was 20mpg. Granted I drove like an old lady.... but still. I couldn't get that on dedicated hwy driving a month ago.

What do I attribute the increased mileage? The spark plugs.
My mileage dropped last summer immediately after change the plugs, and I have always suspected them. of course YMMV.

IF you are having fuel mileage issues, give it a try. I changed out the filter and the diff fluid becuase it was time, but who knows....maybe they helped as well. I know the diff fluid and the fuel filter change didn't HURT!

NGK's plugs came on the 3.4 stock, along with 3 denso's, i would attribute it more towards driving habits than anything. Maybe you got a crappy set of NGK's.

I can understand the line of thinking, I really can.

BUT I can tell you that in the past 10 months I have driven that vehicle like a little old lady, coasting to stops,
easing away from stop signs, etc. with no difference in mileage. I have paid close attention to my driving habits, and I can tell you that the vehicle is getting better mileage now than just 2 weeks ago. My last fillup before the changes I got a whopping 16.5 MPG. that was mostly hwy driving with cruise set on 63mph.

This is what I know for sure: Last spring/summer I changed plugs/air filter and bought new tires(1 size larger than stock) and added shocks and 1" spacer. Mileage dropped by approx 2MPG, consistently. I thought it could have been the new tires, that does happen.
NOW I am getting the mileage I USED to get before the new tires and the NKG plugs....

Everyone can draw their own conclusions....I am just happy to get better fuel mileage

Interesting thread. There are quite a few people who have also said their mileage dropped after changing plugs. Maybe the is something to the Denso/NGK combo.

Of course, when I want good mileage, I leave the 4runner at home and drive the Valkyrie

I recently added a pretty extensive Tune-up section in the buyers guide. Everything you would ever want to know on how to improve mileage.

I would quote that here, but its pretty long.

cool, I will check it out.
Noticing your number of posts, I want to thank you for all you do here.....good Job!

Thanks.

I changed the Oxygen Sensor upstream before the cat on mine and I'm seeing a huge improvement!

What prompted you to change the sensor? Was it throwing a code or did you have another reason to change it?

What was your before and after mileage?

I didn't quite do my mileage yet as I'm still on the first tank, but ususally at half a tank id be at like 80 miles, now half a tank I'm at 106. This is with 50% city 50% highway driving to work at 60-65mph. I'll keep you posted.

I'm sure you know this but when you change tire size that effects both your speedometer and odometer. This means if you calculate your mpg the old fashion way of dividing the amount of fuel you add to your tank by the number of miles driven since you last filled up, you also need to calculate the difference in tire size.

Meaning if you were stock at 265-70-16 and went up one size to 265-75-16 the difference is 3.4% bigger tire. That means if you used to get 300 miles per tank and it took 15 gallons to fill up then you got 20 mpg. After the tire change and lift if you got 250 miles per tank and it still takes 15 gallons to fill up you are NOT getting 16.67 MPG. You need to take 250 miles and multiply that x 3.4%, then divide by 15. That will give you 17.23 MPG.

Pretty sure that's how you do it. Maybe I'm re****ed...

...one thing you can do is install an MPG gauge. There are a bunch of them out there, I've used both the Ultra Gauge and the Scangauge II (the SG is currently installed.)

Both of those gauges give you an 'instant mpg' readout that will tell you your MPG at any given moment. By watching this you can see when to keep your foot off the throttle and let it coast - you may be surprised at how this can help you boost MPG.

Of course, these devices don't neccessarily "pay for themselves" (as is sometimes advertised) but they provide a lot of other good diagnostic tools as well and can also be used to see what code is being thrown when you get a CEL. It will also reset the CEL for you.

Yes, you need to apply a correction to your miles driven. You can either use the nominal size difference, or you can use a GPS to measure the distance to determine what your multiplication factor should be. Set the GPS tripmeter to zero, then set the truck tripmeter to zero, drive about a hundred miles and then divide the GPS reading by the Odometer reading to get your multiplier.

IOW if the GPS shows you went 105.5 miles and the Odo shows you went 101.5, then 105.5 / 101.5 = 1.039. Now when you fill up with gas, take the odometer reading, multiply it by 1.039 and divide that by the number of gallons and you have your true MPG.

Yep, I am aware of the distance correction needed with larger tires.


This is what I do....