3rd Gener's with 4.88's ....mpg?

[Applejack]

Hey all you guy's with 3rd gen's who have made the switch to 4.88's, what is your average mpg? Also it would be helpful to include some general build specs.
Already I have posted my disappointment in their lack of any noticeable performance gains. But at least, at the very least I was hoping to recover some lost mpg's but after running through my first tank with these gears my mpg's have dropped even further. I was averaging 13-14 mpg mixed driving now I'm down to a dismal 11.5.
My specs are:
'99 Limited
Brand new transmission
265/75/16 ST Maxx tires
ARB bumper with winch
OME lift (2.5/3inch)
Sliders
Budbilt front skid
So a little heavier than she used to be.

 

[p nut]

Assuming that says "265/75/16", why 4.88's for <32" tires? Just curious.

Perhaps too low of a gearing = keeping the rev's high on the freeway. But maybe something else is going on.

 

[AxleIke]

How are you calculating your MPG?

In a 99, the speedo and odometer are read from the ABS sensors at the wheel, NOT the transfercase. So you should not have changed how you calculate the MPG from before the gear swap.

Even though the stock size is 265/70R16, my truck read dead on with 265/75's when compared with the GPS, so you should be able to calculate by just dividing miles by gallons, with no other corrections. Check it with your GPS, but I'd bet you are pretty close to dead on.

 

[Applejack]

Assuming that says "265/75/16", why 4.88's for <32" tires? Just curious.

Perhaps too low of a gearing = keeping the rev's high on the freeway. But maybe something else is going on.

Yes 265, I went with 488's for help in coping with the extra weight my 4runner has gained, add to that when we load up to hit the backcountry we just add a bunch more weight. When we travel we are usually running anywhere from 5200 to 5600 lbs and it never has liked that and especially when we tow our trailer.

As far as calculating mpg, yes, I just divide the miles by gallons used. Today it was 161 miles/13.9 gallons. Speedo is pretty dead on with this setup. GPS verified.

 

[MT6bt]

Is that with a trailer? That's rough. When I had my last 4runner (RIP 2000 5SPD 4.10 gears 265/75/16 cooper stts)
I was getting 18-20 avg with ~750 lbs cargo. Sounds pretty brutal!

Ah, crossovers: car like off-road capabilities, minivan looks, and truck fuel economy...

 

[Applejack]

Is that with a trailer? That's rough. When I had my last 4runner (RIP 2000 5SPD 4.10 gears 265/75/16 cooper stts)
I was getting 18-20 avg with ~750 lbs cargo. Sounds pretty brutal...

No, that 11.5 mpg is unloaded, half city half highway driving.

 

[CYi5]

15.5 cty / 17.5 hwy is what I usually see. Moving to Oregon recently, the 55 mph speed limit helped a little bit for highway.

 

[Applejack]

Welcome to Oregon. My brother lives in Bend so I'm usually up that way once a month or so.

 

[AxleIke]

As far as calculating mpg, yes, I just divide the miles by gallons used. Today it was 161 miles/13.9 gallons. Speedo is pretty dead on with this setup. GPS verified.

Holy Crap. I dunno man, I think you may have something else going on. I just can't believe you are getting that bad of mileage with a healthy motor. I've got a lot of extra weight (more than you), plus bigger tires (285's), and while it is a 5 speed, it'll still do 19, and I'm not geared as well as you are (4.3's).

I'd look at the plugs, air filter, and throttle body and make sure you aren't running REALLY dirty. Thats pretty bad, and I think there is an underlying cause.

 

[Martinjmpr]

Why would you think that going to lower gears and making the engine turn faster at a given speed would increase your MPG? Does that ever happen?
.
Increased power? Yes. Increased mileage? I don't see how that's even possible, unless you're running oversize tires and the purpose of the lower gearing is to compensate for bigger tires, but you're running stock size tires.
.
I would point the finger at the slushbox. I hated that damn thing on my '99. Combine the lackluster power of the 3.4 with the power-robbing slushbox and add in a stupidly undersized 18.5 gallon fuel tank and you have a recipe for a vehicle with a completely inadequate 225 - 250 mile practical range between fuelups. My Tacoma had the same engine but a 5 speed manual and I could get 19 - 21 on a pretty regular basis even running 32" tires.

 

[v_man]

Why would you think that going to lower gears and making the engine turn faster at a given speed would increase your MPG? Does that ever happen?
.

x2 ... I see this belief in other posts all the time , that some how adding lower gears increases your MPG ...

First thing I'd do is a complete tune-up and make sure the motor is tip top ...

 

[Martinjmpr]

Yeah, I could understand if you were running bigger tires (which effectively gives you a taller gear ratio) then that might cause the RPMs to drop below the peak torque and make the engine "lug", then going to lower gears would have the effect or restoring the original gearing. This might make a slight MPG improvement except that of course you also have to factor in that bigger tires and wheels are almost always heavier than small ones so even though you might be back at the same effective gear ratio, you are moving more weight with the same power so I'd still expect MPG to go down.

 

[AxleIke]

MPG's won't go up, but his mileage was bad before. 161 miles a tank is not something I'd want to deal with for long.

I think something isn't working quite right, either the engine is running badly, and for some reason no codes are popping, or the transmission is screwed up.

OP, when you had the new transmission put in: what happened to your MPG? What was the reason for the swap? Was the transmission new, rebuilt, or used and swapped in? How are the shifts?

Also, is your check engine light working? If the bulb burned out, you could have all manner of codes but not know it.

 

[p nut]

Might try the basic tune up like AxleIke said--plugs, clean MAF and TB. That is just way too low.

 

[AxleIke]

I should also mention that I'm using (perhaps wrongly) a 98 4runner as a reference for what I assume automatic trucks should get, even modified. Its a 98, automatic, 285/75/16's, stock 4.3 gears, a 2.5" old man emu lift, and a supercharger. It is admittedly not hauling around the extra weight of the OPs truck, but some of that should be offset by the larger tire width and diameter. He see's 16-17 mixed, 15 ish for stop and go city, corrected for the tires (checked by GPS).

One other thing to check, OP, is that your truck isn't sensing from the tcase. I was told by a tech that I know that 99's were ABS sensed for the speedo, cruise, odometer, etc... Might be worth a quick check under your truck that you don't have a speed sensor on your transfercase. That could make the difference in MPG you are seeing. (correcting for the gear change, you are back closer to 13). I doubt it, but worth a check.