874runner

I was just reading on the "Post your gas mileage" thread. And i noticed everyone seems to be getting way better then me even the v6's. I don't understand... heres my set up

874runner 22re 33" tires and 4.10 gears.
I get on average about 14 mpg in town and highway maybe 16-18

I've done the tuneups on it air filter fuel filter new plugs even retimed the thing... any ideas of what could be causing me to get such horrible mpg?

Belize Off Road Team

Tire pressure for one thing.

874runner

i just got brand new tires... which are 10.50's instead of 12.50's that i had on before... it didnt seem to change much and i'd think the tire place would of put the correct pressure in ill have to check that though.

Jay351

GEARS!!! You need 4.88's to bring you back to stock.

Also check for pre-o2 sensor exhaust leaks.

874runner

o2 sensor sits in the manifold right? cause i had my exhaust break off right after the manifold on a trip lol driving on just the manifold till i could find a shop to reweld it that was annoying...

I was also wondering about the gears should i go 5.29's? or the 4.88's? id like to go 35's in the future.. i cant even use 5th gear unless i am going down hill... lol

Jay351

If you plan on going with 35's soon go with 5.29's You will rev a little high while running 33's but you will have great accel and will be setup for 35's.

As for as I know, the o2 sensor on our trucks is bolted right before the cat. I don't know if that changed in 89/90 or not.

Matt16

Unless you have corrected the speedometer, you are getting 16.8mpg in town and 19.2- 21.6 mpg on the highway. Pretty bloody good if you ask me. That's about what I get with 31's and a 4 cylinder

tc

Tire pressure: Tires are cheaper than gas now, run them a LITTLE on the high side.

O2 sensor: Seems the computer has a wide tolerance for bad O2 sensors before lighting the CEL. Just because you don't have a CEL doesn't mean the sensor is good. If you don't know that it has been replaced, get a Denso or NTK (same company as NGK) O2 sensor.

Gearing: you will get better milage with 5.29 than 4.10 because you won't have to constantly have your foot on the floor to hold speed. The difference between 4.88 and 5.29 is only about 200 RPM on the highway. MUCH better to have our rigs geared too low than too high!

88wildrunner

what does the speedometer have to do with it, you calculate the MPG with the odometer. i am also getting unusual low gas milage about 15 avg. i used to get around 19mpg a few months ago.

Matt16

I should have been more specific, I meant odometer, but its driven by the speedo cable.

Right now, for mile your odometer says you've gone, you've actually gone 1.2 miles as you tires are bigger than stock (28").

vermontoyota

speedo and odo run off same thing. If you put bigger tires on both are innacurate- they indicate you are going slower than you are and have gone less distance than you have actually gone.

the speedometer and odometer function off number of rotations the tire makes and the calculation is done assuming stock tire size. so if 29"s are stock and the odometer tracks your truck going from your house to the store and the wheels rotate 500 times you have gone (500*3.14159*29inches*(1foot/12inches)*(1mile/5280feet))=.71895 miles.

if you have 33"s and the odometer recorded 500 rotations of your tire it would report the same .70559 miles but you would have really gone 500*3.14159*33*1/12*1/5280=.8181 miles. so you're speedo is off by a factor of around 12%.

to correct this multiply any speedometer or odometer reading by 1.12 or just 1.1 (add 10 percent). so next time you fill up and your odo says you went 400 miles, know it was more like 440 miles. I think this is the reason why a lot of people think they are getting worse gas mileage than they are

on a final note for driving riggs modified for offroad use that are as old as me I dont think what you guys are getting is that bad, especially after you corret the numbers your odo is spitting out

874runner

well i never really thought about the tire size for gas mileage thats a good point... i mean i thought about it for speed but tire size it never came to my mind. but yes i do go off the odometer reading so that could be why it seems so horrible...

tc

For those of you correcting your odometer readings, STOP IT!

The ONLY value they have is in comparing on your truck before and after. There is enough error in the speedo from the factory that it is pointless to keep converting them for any other reason.

Compared to GPS, my speedo was off the following amounts with the various combinations:

31/4.56 - Stock. Never measured, assumed it was right
33/4.56 - Less than 1% error (essentially dead on)
33/4.88 - 5% off - should be same as stock

Matt16

I meant, "have you corrected for your speedo". For the benefit of others (I'm sure TC figured this out when he was in diapers) when you up your tire size, you perceived mileage will drop. This is because for every mile you travel, the bigger tire rotates less often than a smaller tire. Thus when you've got say 250 miles and you're empty, you've actually travelled 300.

This perceived loss of mileage is compounded by the fact bigger tires weight more. Every pound extra you have on the tires slows you down the same as if you have 10 pounds in the truck. Say 33s weigh 20lbs more than 31s (just a guess), you have 4 tires, so that's like having 800lbs in the truck. Furthermore, as bigger tires reduce the the effective gearing, you tend to push the skinny peddle down a little more.

Other small factors that kill mileage are:

• wind drag to the the larger frontal area of the tires (on the highway, this makes a difference)
• often when people go up a tire size, they buy something more aggressive- more rolling resistance
• You are higher off the ground thus more air passes under the truck and gets caught in the turbulance created by the undercarriage.

wind drag due to the larger frontal area of the tires.

vermontoyota

stop correcting odometer readings? how do you figure? Tire size changes definitely effect readings.

i know computers are playing more and more of a role in vehicles but i'm pretty sure the rims don't send a code when somone jams some bigger meats on them.

just a 22re

as for the gps doing it for ya ha ha good luck with that one! i have a gps a very good one its a tomtom one and yes it says where going 70 miles an hour but no where going 68mph why do they do this to make you think your going faster then you are. ie.. to slow down.prof yes on a simi that has 30k on it my cos car that has 2k on it and my moms and dads rental that had 275 miles on it all did the same as for my rig dont know as my speedo dont work and think of this everyone


WHAT GOES UP SOMETHING MUST GO DOWN!!!!!!!

power adders hp up fuel down
tyre size up fuel down (unless you regear)
power down fuel up

think about it people

tc

Because people get in such a tizzy assuming that their speedo was right from the start, when IT'S NOT.

I should be more clear - if you are comparing YOUR TRUCK before/after, you MUST correct for the speedo difference. The rest of the time, it's absolutely pointless. Especially when comparing BETWEEN trucks, as there is no way to know how accurate their speedo was in the first place.

874runner

that is true tc

vermontoyota

okay tc i agree with you there.

rbmoomba

'88 runner with rebuilt 22re, going on 800 fresh miles. I'm getting 17mpg on 33 x 12.50's with stock gears. No problem shifting into 5th and passing traffic. Speedo says 65-70 and i pass people left and right with no problems. I need to line up with someone in a stock vehicle to check what that speed actually is.