Gamefreakgc

Mine reads high as well. If you have 225's on it and you've got the SR5, your tires are too small. The odometer will read roughly 9% higher (91 miles equals 100 on my odometer). I'm waiting on the treads to wear out before I buy 31's the correct size for these models.

But some of you might be saying, "my door jamb sticker says to run 225s!". It's been documented that the SR5's made in Japan (J VINs) were made with 225's on them to have lower taxes. Once shipping to the US, the dealers put 31's on them to match the speedometer gears. You can search these forums for my research if you feel bored. That has most of it.

Just take it a few steps at a time, don't empty your bank account to save $5-$10 per fillup at the gas station . Although in the long term, the fuel savings will add up. My cat-back exhaust system has already paid itself off ($275) in gas savings since this is my daily driver, I had it put on in August of 2012. And that's only with a 12 mile commute each day.

lectric80

Ok, thanks for all the info, but there are some things that cannot be done safely.

My commute is a total of 74 miles a day:

12 miles at 30-40 MPH
approx. 20 miles at 60-65 MPH
The remaining 42 miles are 75 MPH

These are the posted speed limits for my drive. Driving 55 on the freeway is not an option, number one because it is unsafe and number two because it will get me pulled over frequently. All the city driving I tend to stick close to the limit, and use 4th gear for all speeds of 35+. The 60-65 MPH zones I also stick closely to the limit, and use cruise control at all times. In the 75 MPH zones I tend to stick (now) between 65-70. RPM's tend to remain around 2800-3000. I know this isn't ideal, but neither is getting killed by the idiots on the freeway.

Tires are 31x10.50's, they are an all terrain tread by Falken, and are at proper pressure.

I have only owned it for just over a week, so there is a lot of unknowns about the current state of fluids and other things. While I will address these, this is my DD and will remain so until the 90 pickup is fixed.

What I'm trying to work out, is what things will work to improve the economy. A lot of you have given great advice, and I do appreciate it. I hope to work through this a little at a time, as I can afford it, and will report back on any and all improvements to the economy. I just find it hard to believe that a pickup, which is lighter obviously, can get 10+ MPG more than the Runner. I truly believe there is room for improvement to this thing, and some of you have reported that you are getting better than mine is currently, leading me to believe it is possible to improve this. Especially since the 16.5 was based on the innacurate odometer readings, in reality it is closer to 15 based on the number of miles I know I had in that tank.

I do know the muffler is showing a lot of rust, so I know it will need to get replaced at some point anyway. I also know that the cat collapsed on my pickup, so I want to put a new cat in just to keep the exhaust flowing. I don't have to meet emissions here, but I'm not going to drop the cat just for a slight power gain.

Thanks again everyone for the advice and tips, I will be experimenting and report back as things progress.

Gevo

If this is the case, then I am getting worse mileage than I am reporting.. I have a feeling i'm still running rich ....

Thanks for the education Gamefreak..

xfactor203

I've always wondered about that. . . Having heard SR5's came with 31's and all. My speedo STILL reads high even with proper spec tires (31's on an SR5)

millball

If you are actually traveling more miles than your odometer records, your MPG calculations will appear lower than they really are.
Nothing can be taken for granted with these old instruments.
Clock your odometer over some measured mileposts on the highway to see what, if any, error exists in true distance measured.
I also use my chronograph watch to determine true speed over ground.
Measure the seconds required to cover the measured mile between mileposts and divide 3600 by this and your answer will be MPH.
I guess GPS and Smartphone apps can do these measurements and calculations automaticly, but I am a simple, old fashioned guy, and a watch is good enough for me.
Just because your speedo is fast, don't assume that your odometer is reading more miles than you have covered.
My JunkRunner reads 9 or 10 MPH faster than actual speed, but the odometer error is on the other side of correct, reading about 92 miles when 100 miles have actually been traveled.

shar

does the spark plugs makes any role to improve gas mileage. I seen lots of advertising about them????

chefdave

Hi
i use denso spark plugs one of the best for toyota engines. may even be orginal factory fit. used them in wifes 3.0 litre legacy a renault laguna and my toyota v6. Renault has covered 20k miles with no probs and got dealer fuel figures. 45+ mpg cruising at 70mph. so i have stuck with them as i know they work but eveyone has their favoriate plug.

lectric80

You are correct millball, however in my case, and it sounds like others, the miles recorded are higher than what are actually travelled. In my case it wasn't a big difference, only about 30 miles more, but that is significant in trying to calculate actual miles travelled.

I will check out the apps for my phone and see if I can add something to record the actual miles travelled in the Runner, as long as I can lock out miles travelled in the Durango.

Matt16

Are you factoring tire size? Check your door frame for tires size, probably came with 235/75r15s and decent chance you have a size different than that. Bigger tires are going to make it look like you haven't travelled as far as you have because they rotate less/distance. So you 16mpg might be 18mpg and you're odometer doesn't know it.

16 isn't horrible for a 3vze.

lectric80

As I have explained earlier in the thread, I know what the door jam sticker says, but my vehicle came with 31's, and my speedo reads higher than I am actually going. This has been verified by roadside speed checks and police radar. When my speedo shows 70 MPH my actual speed is 65. This means, and I'm planning to verify this in other ways, that the mileage racked up on my odometer is higher than the number of miles actually travelled. At least that's the assumption I am running under at this point, I am checking on some apps to load onto my phone so I can attempt to track the mileage more accurately.

RSR

Could be your gearing too. The speedometer is spec'd to a gear ratio and tire size combo.

The best thing you can do for MPGs is drive slower.

The relationship of drag and speed: http://www.trucktestdigest.com/axle%20ratios.htm
Also, synthetic gear oils in your differentials. Keep your driveshafts well greased as well. Synthetic engine oil helps with MPGs as well -- most of this improvement is seen at cold start but they also lubricate better, so should reduce drag for better efficiency. Same also applies to your tranny fluids.

Last thing with fluids is that the lower the ethanol in your gas, the better. 1) our trucks fuel systems weren't made for it so can cause serious headaches, and 2) 10% ethanol gas reduces your MPGs by 5% over 100% gasoline and E85 (85% ethanol) gas reduces your mpgs by ~1/3rd. I don't think the higher octane fuels are necessary in our trucks unless you're manually tuning your engine to either run significantly advanced (beyond 12* btdc) or to run lean in open loop and want to minimize chance of knocking and/or burned pistons.
Where you buy gas matters too. I like Shell, but I'm sure others have their preference too.

The orange flamethrowers or other fuel injectors that atomize would help too.

Replace your PCV valve and grommet. Make sure you have no vacuum leaks. Make sure none of your vacuum switches are broken.

Once you run all the engine and intake cleaner through, go ahead and replace your O2 sensor. It's critical for maximizing MPGs and it's performance/sensitivity degrades over time as exhaust carbon clogs its element.

I find much above 65, my truck seems like it can't breathe. That is, it's running rich -- adding fuel but not enough air is able to come in to make a difference...
BUT, to do the Supra AFM swap, you need a wideband 02 sensor on your rig.

FWIW, running in the 65 to 70 range on relatively flat highways I'm low to mid 17 mpgs. Above 70 and I'm in the mid 16s... I don't have a lot of opportunity to safely test sub 55mph speeds and mpgs for any measurable distance here in Texas. It's either stop and go or 65+ where I'm located.

Lastly -- and this is important -- test all of your sensors you can get to and make sure they're within spec. All temp sensors, spark, air, fuel sensors, etc, need tested to ensure they're within spec. On these old trucks, usually only major failings give you the CEL...

With above and Gamefreak, you should be good.

lectric80

Good info there, thanks.

As for changes,right now I have only changed the way I drive. I'm conscious of the RPMs when I shift, shifting at about 3300 when accelerating onto the freeway and highway. I have also been sticking to 65 to 70. This has resulted in 18.1 MPG.

I've decided to use the 16.5 as a base to monitor improvements going forward. Eventually I will figure out the true mileage,but for now this will work.

Gamefreakgc

RSR's got it, if you have 31's and your odometer is still reading high (as in 100 miles on odometer is only 91 miles according to google maps, gps, etc.), then someone probably switched out your gear ratios at one point or another. There's no Toyota 4Runner or Pickup that came with tires larger than 31's from the factory or dealer. In this case, your MPG's are inflated too high.

More commonly, your odometer reads low because you are running larger tires than the stock gear ratios. This means 91 miles on the odometer is actually 100 miles according to the gps. This means your MPG's are deflated and higher than your readings.

xfactor203

That's a thought. . . Not that it matters much to me. I know it reads fast. I tend to drive slow regardless (well, on pavement anyway).

I made no assumptions about odo accuracy and speedo accuracy being related. But, now that it's been brought up, how DOES the odo record mileage if not from the speedo head?

All this talk of mileage makes me feel like I should figure out why mine has taken a nose dive over the last few months. Sigh.

xfactor203

This seems extremely unlikely in my case. I haven't changed gears, and the truck was a suburban kid hauler until I got ahold of it. My thought was maybe it came with a mismatched gear / tire / speedo combo from the factory.

Gamefreakgc

No, it wouldn't be mismatched. What I mean about inflated or deflated MPG's is that the gearing doesn't match up to the actual distance traveled.

Your MPG drop is just due to age, plain and simple. The engine is less efficient and takes more fuel to go the same speed as before, parts and sensors are failing (changed your oxygen sensor lately?), drive train is becoming worn and sticky. Everything goes from order to disorder.

Thought I would add this calculator so you all can have fun with your gps speed readings and tires sizes today: http://www.wallaceracing.com/gearcalc1.php

xfactor203

Yeah, I agree. I didn't think the speedo error had anything do with the mileage drop issue. The speedo error comments were more of a "gee whiz, what could be going on here" sort of thing.

Now that I think about it tho', it's plausible that gearing COULD have been switch by a previous owner, not b/c they WANTED a different ratio, but because they replaced worn or broken parts from a donor vehicle that happened to have different gearing.

Gamefreakgc

Yeah, it's possible. There's different colored "dots" and other marking to designate the gearing on the drive shaft but not everyone knows what that means in terms of ratios. But having a lower ratio is desirable (meaning more engine rotations per wheel rotation), especially for off-road. The Auto trans 4-speed ratios are the least wanted ones, unless you are never going to take it anywhere but a freeway.

lectric80

I'm sure it is possible the ratio was changed, but I just know both my 90 pickup with 31s and my runner read high.

RJR

The speedometer on my '94 4Runner with 31's reads about 6-7% high (reads about 48 mph when going 45.) However, when I got the computer program going that reads ECU parameters from the diag port (see my recent post in Gevo's smog thread), the mph that the ECU reports is dead on.

So, it seems like the speed sensor is accurate, but the meter itself in the dash is not so great. Makes sense, I think. The speed sensor is likely just a pulse generator, which the ECU counts to measure speed. With a crystal controlled clock, it can do that quite accurately. The speedometer in the dash turns that pulse train into an analog voltage and then applies that to a meter movement. Both of those steps have extra opportunities for error.

I haven't checked my odometer carefully, so I don't know how accurate it is. My guess is it's better than the speedometer.