Another "help, terrible fuel mileage thread"

[maxspeed96ct]

I have a 99 4runner 2.7 auto.

And my gas mileage is just terrible. Has been since I purchased it back in Nov.

After calculating my last tank I got 13.4 mpg with a mix of 50 city 50 highway .

I have recently changed out my plugs to NGK plats, and installed new NGK wires. Installed a trans cooler and did a trans fluid flush aswell .

What Should I try next, I was thinking of installing a high flow cat. But my buddie said it might make my truck run rich and make mileage worse.

What else can I try ?
Im running out of ideas....

 

[YotaZach85]

Try cleaning the MAF and the throttle body, I can usually tell a difference in mileage after changing the rear differential fluid, you can also try replacing the front o2 sensor. How many miles are on your truck?

 

[maxspeed96ct]

Try cleaning the MAF and the throttle body, I can usually tell a difference in mileage after changing the rear differential fluid, you can also try replacing the front o2 sensor. How many miles are on your truck?

Truck has 123k

I plan on doing the rear diff fluid next just waiting for a warm day.

For the o2 sensor, are the aftermarket ones just as good?

 

[YotaZach85]

Truck has 123k

I plan on doing the rear diff fluid next just waiting for a warm day.

For the o2 sensor, are the aftermarket ones just as good?

I think I remember seeing the o2 replacement being reccomended at 100k...stick with Denso though. - Underdog Racing Development used to have some good deals on Denso o2's but I haven't checked in a while. Just do the front sensor the rear shouldn't effect your fuel mileage.

 

[maxspeed96ct]

I think I remember seeing the o2 replacement being reccomended at 100k...stick with Denso though. - Underdog Racing Development used to have some good deals on Denso o2's but I haven't checked in a while. Just do the front sensor the rear shouldn't effect your fuel mileage.

Ya I understand, the rear just checks if the cat is working.

Whats your opinon on changing out the cat, would the high flow cat cause my truck to run rich ?

 

[4-Ripcord]

Don't forget your air filter.

And x2 on Throttle body and Mass Air Flow sensor.

The little stuff can make a big difference.

 

[YotaZach85]

Ya I understand, the rear just checks if the cat is working.

Whats your opinon on changing out the cat, would the high flow cat cause my truck to run rich ?

High flow cat didnt make any difference on my 3RZ Tacoma, the only reason for the cat holding back fuel mileage is if it's getting clogged but you would notice an extreme power loss. Have you tried Seafoam? My Tacoma loved Seafoam, I ran it every other oil change and could pick up 1-2 mpg but I did it pretty regularly so you may be able to pick up more if you've never done it..

 

[maxspeed96ct]

Don't forget your air filter.

And x2 on Throttle body and Mass Air Flow sensor.

The little stuff can make a big difference.

Air filter is new, Ive been affraid to spray anything on the MAF but I think ill give it a shot. Checked out some MAF cleaner at the sotre the other day but didnt grab it.

 

[YotaZach85]

Air filter is new, Ive been affraid to spray anything on the MAF but I think ill give it a shot. Checked out some MAF cleaner at the sotre the other day but didnt grab it.

Make sure you use throttle body cleaner when you clean the TB, too it makes a world of difference. And the best way to clean it is to pull it off so you can get at the IAC motor, they're good for getting carbon build up and not operating smoothly.

 

[Tomsriv]

02 sensor and MAF sensor, but I would think you would have a trouble code if they are that out of whack. If you don't have any codes I would do diagnostics with a vacuum gauge. See article on how-to
Vacuum gauge diagnostic check

 

[YotaZach85]

02 sensor and MAF sensor, but I would think you would have a trouble code if they are that out of whack. If you don't have any codes I would do diagnostics with a vacuum gauge. See article on how-to
Vacuum gauge diagnostic check

They don't have to fail completely to throw a code or screw with mileage.

 

[maxspeed96ct]

High flow cat didnt make any difference on my 3RZ Tacoma, the only reason for the cat holding back fuel mileage is if it's getting clogged but you would notice an extreme power loss. Have you tried Seafoam? My Tacoma loved Seafoam, I ran it every other oil change and could pick up 1-2 mpg but I did it pretty regularly so you may be able to pick up more if you've never done it..

I used the sea foam but I didnt suck it through the brake booster like I see in some of the other threads. i need to try that method next.

As far as the cat being clogged , I have no cell . But Its hard to tell if I have power loss since the 2.7 4runner with the auto is a bit a slug as it is..

Found a front o2 sensor on rockauto for 70$, going to give that a shot before I order a new cat and go from there I guess.

 

[YotaZach85]

I used the sea foam but I didnt suck it through the brake booster like I see in some of the other threads. i need to try that method next.

As far as the cat being clogged , I have no cell . But Its hard to tell if I have power loss since the 2.7 4runner with the auto is a bit a slug as it is..

Found a front o2 sensor on rockauto for 70$, going to give that a shot before I order a new cat and go from there I guess.

Your cat should still be good at that mileage, I didn't change the one in my Tacoma until around 210k when it started breaking down and making noise.

 

[Limited2K]

Make sure that new O2 sensor you go with is Denso. that will help from throwing future codes with bosch products or similar.