Extremely low gas mileage

[JohnsD90]

Ive just been reading through this thread and thought i might throw out a few thoughts, my gas gauge seems to be working quite fine, when the gas light comes on ive gone about 180-200 miles, this takes about 16.5-17.5 gallons to fill up, I think if you have a lift on your 4runner it could mess with you reading a little bit, for example most rigs that are lifted on here arent sitting level...the rear is higher, could defiantly be messing with the reading on your fuel gauge right....? also if your running a bigger tire than stock your odometer isnt completely accurate, you've actually gone farther than what it says, how much farther..just depends on how much bigger tires your running, but probably not to much of a difference, but it all adds up in the end, around town i get 10.5-12mpg, the best ive gotten on highway was 14.25mpg and that was on a road trip, im figuring most of this is due to my 295/70/17 Toyo M/T's, cuz when i was bone stock 5 months ago i was getting 22-24mpg highway, and the only things that have changed since is tires, lift, and intake. so just my opinion....tell me if im completely wrong....??

In your case you are still prolly gettin 16-18mpg its just that your miles are F'd up and it comes up as 12-14.

 

[Perrone]

Good information from everyone so far. Thanks for all of the advice. I think those of you who said it were right about my engine never really getting warm, which is true because my drive is so short.

 

[4ganger]

Tmaxx13 Nice rig. Reading around on the inter-web this weekend you are spot on with your thoughts. Bigger tires will affect calculated gas mileage. You can figure it out with a mathmatical formula based on the size and mileage if you really wanted to.

Rough math would do it - if your odo is off by mileage due to tire size just have to figure out what is being reported vs. actual. If say your rig is saying it went a mile but in reality it is only going 9/10th of a mile that is 10%. Add 10% to the mileage since last fill up (using trip meter) and that will get you the true mileage.

Also - the tire tred style will affect gas mileage. More agressive tread type like an AT or mud terrain tire will generally get lower gas mileage than a smoother riding all season highway tire. On tire rack.com you can search for low rolling resistance tires. Based on an article I read this weekend (can't find it now but its on this forum somewhere) an agressive AT tire vs a more highway tire can be upwards of 2.2 mpg or 15% give or take. That's a lot and something to think about when buying tires.

 

[mory]

My 98 4runner 4x4 r lift with 305-65-17 with 17x9 promcomp 1089,and I getting about 14-14-5 mpg and that 87% city driving stop go alot, 5 mile to work, hopefully i want to get at least 17 mpg i be happy, maybe regear to 4:88 might help.

 

[redlined600]

If you want to get freaked out about gas mileage, get a ScanGauge! It'll show average MPG for trips. You will be getting 11-14 on short trips with lots of stop and go's. I usually average 17-20 mpg. On the highway I have seen averages of 24+.

I found my scan gauge to be about 2~3 mpg optimistic.

 

[performance mp3]

+1 on the front O2 sensor

 

[runrunner]

Winter gas...

I was getting around 17mpg's last summer and that was with 265 Duratracs and a 3" lift. Lately I've dipped down to 15 ish and I attribute that to the winter blend. I'm also running an ARB bumper which probably doesnt help.

I've debated on replacing the O2 sensor, but its a spendy one. Also thought about having the professional fuel injection service completed. It would be nice to get better mileage, but I dont know if thats realistic.

 

[marmotan]

New user here, but not new to Toyota. I just picked up a 99 4Runner Limited and with my first tank of gas got 13.1 mpg. Not good, but mostly short trips in town and a short trip to work (8 miles). I'll keep tabs on it and try to get a freeway trip in so I can see what kind of freeway mileage I get.

If the city mileage stays consistent, I may try cleaning the MAP sensor and throttle body. It has 156,000 miles on it and it appears that the previous owners took very good care of it. All recommended maintenance has been performed and it sure runs smooth.

I absolutely agree that cleaning the MAF sensor will help things. There's a post on here somewhere on how to do it. I did mine (the MAF was disgustingly filthy), and I'm getting better MPGs, plus the engine now idles warm at 700 rather than 1000 RPM.

 

[Perrone]

I absolutely agree that cleaning the MAF sensor will help things. There's a post on here somewhere on how to do it. I did mine (the MAF was disgustingly filthy), and I'm getting better MPGs, plus the engine now idles warm at 700 rather than 1000 RPM.

This would make sense in my case. My idle changes a lot when I'm sitting still. I'll take a look at the MAF this weekend.

 

[marmotan]

question, brian et. al.

i had a CEL come on about a month ago and when it was pulled the clerk at O'Reilly said the code was the O2 sensor. word went through the grapevine and my gramps called me and insisted that i change the plugs before spending ~$120 on a new O2 sensor. so i did (I went with Denso plugs and NGK wires, by the way.). the light went away and hasn't come back. however, i do only get ~14.5 mpg and was averaging that before the new plugs and wires. could my O2 be not working to its full potential, or are there any other factors that are giving me this crappy mileage? my runner is stock.

I've read that our Denso O2 sensors will only function reliably for about 75,000 miles. I found one online for about $50 and just had my muffler shop install it when they put on my new muffler. If you do replace it, don't forget to reset the computer too by pulling the fuse.

 

[ryankmasuda]

I've been reading this thread and I have some questions. I read that changing the o2 sensors can improve your mileage but I've also read that o2 sensors are either bad or good with no in-between in another thread. So does it make a difference if I replace the o2 sensors wether im throwing a code or not? Also I read that our 4runners have four o2 sensors, two above the cats and two after the cats. This looks like an expensive "maybe improvement" on gas mileage. Also is Denso the oem brand o2 sensor? If you could make a list of top 10 things that by replacing or cleaning will improve your gas mileage what would they be? These are what i would think could improve mpg's. (in no particular order) what am i missing?

1. MAF
2. throttle body
3. spark plugs
3 plug wires
4. intake/filter
5. timing
6. tires (size,tread,psi)
7.
8.
9.
10.

 

[brian2sun]

I've been reading this thread and I have some questions. I read that changing the o2 sensors can improve your mileage but I've also read that o2 sensors are either bad or good with no in-between in another thread. So does it make a difference if I replace the o2 sensors wether im throwing a code or not? Also I read that our 4runners have four o2 sensors, two above the cats and two after the cats. This looks like an expensive "maybe improvement" on gas mileage. Also is Denso the oem brand o2 sensor? If you could make a list of top 10 things that by replacing or cleaning will improve your gas mileage what would they be? These are what i would think could improve mpg's. (in no particular order) what am i missing?

1. MAF
2. throttle body
3. spark plugs
3 plug wires
4. intake/filter
5. timing
6. tires (size,tread,psi)
7.
8.
9.
10.

O2 sensors can get old and operate less than optimally without throwing a code and it can affect your mpgs. All 3rd gen 4Runners have two O2s (1 pre and 1 post cat(s)) and they are Densos from the factory.

I'd say add O2 sensor to the list (if it's over 75K and/or throwing a code). Doing a MotorVac induction cleaning helped my mpgs a lot too.

 

[ryankmasuda]

What does a MotorVac consist of?

 

[Perrone]

I finally had some free time on Thursday so I replaced the spark plugs, cleaned the maf, did the deckplate mod, checked air filter, cleaned up the intake and I'm going to clean the TB soon (maybe tonight). I think I'll stop by autozone and grab some of that fuel system cleaner on the way home too.

I have to wait to do the plug wires and O2 sensors for when I get some extra cash. I just filled up right after doing all of this so I'll get back with you guys next fillup and see if anything changed. Thanks again for all of the advice!

 

[MAD 69]

I can't see the deckplate mod helping save fuel - I would think you would lose 1-2 mpg since your gaining 1 or 2 HP...

 

[Perrone]

I can't see the deckplate mod helping save fuel - I would think you would lose 1-2 mpg since your gaining 1 or 2 HP...

Oh I didn't do that for mileage I just wanted to do it for the heck of it. Plus it was something cheap and I felt like i was neglecting my poor baby. If it effects anything too badly I'll just screw the cover on it.

 

[kittkatt99]

Did you ever figure out what was causing the drop in mileage? I am currently having a drastic reduction (down to almost 4mpg), and I changes out the timing belt and water filter. Had a tune up. Now mileage up to about 14 mpg. Better but not ideal. Let me know if you can.
thanks

 

[KingSwingles]

Too many factors

Disclaimer: I can have a lead foot at times but even being gentle, fuel economy is still low.
I have '00 3.4L. I check my fuel economy pretty much every time I fill up (out of habit). I get anywhere from 12-14 city, 16-18 highway. I run 265/70/16 Goodyear Wrangler Duratrac tires and know that the LED light bar doesn't help with drag but I was getting the same numbers prior to its install. I also have a cold air intake.

I installed NGK iridium plugs less than 25k miles ago (rather than the OEM laser platinum plugs) with NGK wires.
I replaced the MAF sensor a Cardone one from Advance Auto (used to work there). The idle lowered from 11/1200 to 7/800.
I have a live data OBDII scanner that allows me to see O2 readings and a friend of mine, who's a certified mechanic, says the numbers look good.
I used to run 87 octane but switched to 93 shortly after to try and help clean up. I periodically use Techron Complete Fuel System Cleaner, which states it can treat up to 20gallon tanks (tried numerous fuel system cleaners on my '00 Camry , when I had it, and it gave me a 3-3.5MPG increase per tank it was used on.

I honestly don't know what else to look into, other than replacing the upstream O2 sensor (knowing its expensive because its an air/fuel ratio sensor). Any input would be greatly appreciated.

 

[CalBlackSheep]

I haven't tried yet, but I've heard changing your coolant temp sensor can help... Good luck!

Sent from my SAMSUNG-SM-G900A using Tapatalk

 

[thegipper]

Disclaimer: I can have a lead foot at times but even being gentle, fuel economy is still low.
I have '00 3.4L. I check my fuel economy pretty much every time I fill up (out of habit). I get anywhere from 12-14 city, 16-18 highway. I run 265/70/16 Goodyear Wrangler Duratrac tires and know that the LED light bar doesn't help with drag but I was getting the same numbers prior to its install. I also have a cold air intake.

I installed NGK iridium plugs less than 25k miles ago (rather than the OEM laser platinum plugs) with NGK wires.
I replaced the MAF sensor a Cardone one from Advance Auto (used to work there). The idle lowered from 11/1200 to 7/800.
I have a live data OBDII scanner that allows me to see O2 readings and a friend of mine, who's a certified mechanic, says the numbers look good.
I used to run 87 octane but switched to 93 shortly after to try and help clean up. I periodically use Techron Complete Fuel System Cleaner, which states it can treat up to 20gallon tanks (tried numerous fuel system cleaners on my '00 Camry , when I had it, and it gave me a 3-3.5MPG increase per tank it was used on.

I honestly don't know what else to look into, other than replacing the upstream O2 sensor (knowing its expensive because its an air/fuel ratio sensor). Any input would be greatly appreciated.

While your MPG isn't great, it's not "terrible" per say. I usually get about 16-18mpg but i drive mostly highway. My rig is also pretty stock like yours.

I'm not sure anything is technically wrong, unless you used to get much better MPG before. There are a lot of variables like driving habits, where your driving (hills ect), elevation, temperature, fuel quality and so on.