Why Such Varied MPGs w/ 3.4 V6?

[Bstrom]

Just got done reading the ECT on/off experiment thread and noted the wide range of MPGs with the different respondents.

I have new plug wires and correct OEM Denso copper plugs, new air filter, a clean MAF and throttle body. Changed the fuel filter and run 89 gas. Did the deckplate mod which didn't do as much good as it did on my '03 Tundra with a 3.4 V6. I'm getting pretty low fuel mileage - around 15 or 16 at best. About half and half highway/street so fuel mileage is probably the actual average.

What accounts for a 3-4 mpg difference between vehicles of the same gen? Seems like I should be closer to 18+mpg but it seems unattainable. Any ideas?

 

[ShooterMcGavin]

Just to throw in my 2 cents... the stock/modification level of these trucks on this forum is pretty varied. Some are fully stock, all the way up to big tires, armor, even new gearing. Then, it's an older vehicle with a range of levels of maintenance in its life for different owners. Many people don't know the full maintenance history, which makes getting a baseline MPG difficult. Driving styles vary, auto vs. manual, terrain (plains driving vs. mountains and trail driving). I don't think it is one thing, but there are several causes.

 

[Bstrom]

Just to throw in my 2 cents... the stock/modification level of these trucks on this forum is pretty varied. Some are fully stock, all the way up to big tires, armor, even new gearing. Then, it's an older vehicle with a range of levels of maintenance in its life for different owners. Many people don't know the full maintenance history, which makes getting a baseline MPG difficult. Driving styles vary, auto vs. manual, terrain (plains driving vs. mountains and trail driving). I don't think it is one thing, but there are several causes.

I hear you on all counts - mine was dealer serviced by the original owner. I'm at 190k miles running 265 Michelin LTX tires, BTW. Use full synth oil too.

Can't help but think the #2 O2 sensor (behind cat) might be getting old and giving weak readings, etc. No engine codes, though. Just a guess but I've got nothing left to imagine what is making the difference.

PS: Are EPA mileage estimates done on flat ground?

 

[Unner]

How hilly your terrain is around you makes a huge difference in these trucks since they don't have a whole lot of power and end up downshifting to maintain speed. Also running the AC in the summer makes your MPG worse.

 

[DK327]

"For better mileage, adjust the nut behind the wheel"

In all seriousness, like stated I think mileage you get will depend on a lot of factors, vehicles mechanical condition and your driving habits... This is why it probably varies so much. I get anywhere from 13-16mpg city driving and 19-21mpg highway depending on speed...

 

[pluton]

EPA measurements in this vehicle's era were done on a dynamometer and 50 MPH was "highway" driving. Most of the difference between different owners' mileage is driving habits, IMO. Hills, wind, A/C are factors as well, especially hills. But there is a very wide variance between what different folks consider "normal" driving. Very, very wide.
I have only ever measured mileage on long highway trips, where I can go the same speed on fairly flat ground for a hundred miles or so. I get 19MPG with my '97, 75MPH, A/C on.

 

[etc.]

I get similar mpg as you.

Some of these mpg claims on this forum are very hard to believe.

 

[AntleredRuin]

There also is acceleration to take into account.
If you NEVER go above 2k RPM, your MPGs will thank you, although it's obviously less fun to drive. Just stay in the right lane.

I've gotten 22.7 MPG before with 99% freeway driving at 60-65. I only floored it when absolutely necessary (merging from the on ramp. Safety first.) I stayed in the right lane and hovered right at 2k.

Don't let your cruise control accelerate for you; it goes WOT to get you to speed faster and often kicks the tranny down a gear to do this.

Any extra weight makes a difference. Don't carry around camping/ trail gear if driving in city, etc. It takes that much more fuel to get up to speed.
Don't tail people. While this in itself does not result in lower MPGs, the mindset behind it does. Get to the speed limit, set cruise control and turn on the radio. Stay far enough back from the people in front of you that you can often just 'pause' your cruise control when you see their brake lights vs hitting your own brakes. Then just 'resume' as necessary. Maintaining a constant speed is necessary. If you're constantly trying to get 4000lbs up to speed, you're wasting a lot of gas compared to just maintaining speed.

What's funny is that if you think about it, technically you get worse MPGs the more full your gas tank is. Gasoline weighs about 6 pounds per gallon, so depending on how full your tank is, the overall weight of the vehicle can vary by well over 100lbs, which can affect your MPGs.

The 'problem' with these vehicles is that they are actually pretty powerful, but don't feel like it right off the line. Especially with the deckplate, ISR, etc. You have to get to 2500-3000 to really feel it, and then you're just wasting gas.

You didn't mention it, so I will assume you have not done it; do a SeaFoam treatment, change the PCV valve, and reset your ECM by pulling the relay. This all can help a lot, especially if it's a 'new to you' truck.

AC is a factor, but I've heard that not using the rear defroster specifically can make a huge difference.

 

[JayRolla]

Just got done reading the ECT on/off experiment thread and noted the wide range of MPGs with the different respondents.

I have new plug wires and correct OEM Denso copper plugs, new air filter, a clean MAF and throttle body. Changed the fuel filter and run 89 gas. Did the deckplate mod which didn't do as much good as it did on my '03 Tundra with a 3.4 V6. I'm getting pretty low fuel mileage - around 15 or 16 at best. About half and half highway/street so fuel mileage is probably the actual average.

What accounts for a 3-4 mpg difference between vehicles of the same gen? Seems like I should be closer to 18+mpg but it seems unattainable. Any ideas?

Your gas mileage seems perfectly fine. My 1996 was rated for 15 city, 18 highway. Thats best case scenario. 2002 was rated 17 city, 19 highway. I have never seen over 19 highway even when I was on stock tires. Best I get in city is 14-16mph with mixed highway.

 

[T4R2014]

I've gotten 19 doing a steady 80 mph from NYC to central NJ and back with three passengers. It's a totally stock 1996 SR5 with 4.30 gears. I only run street tires. Otherwise, my average mileage figures around 15-16 mpg.

 

[WallyWest]

Biggest factor is driving style.

Try to avoid using the brakes, like ever. Make a game out of it. Every time you touch the brakes your gas mileage goes straight to hell. Ok, obviously you have to use them to come to a full stop and around town it can be tough. But drive with the gas pedal as much as you can. That means leaving plenty of room between you and the car in front of you, and carefully watching traffic patterns ahead of you. Instead of stomping the brakes you can then simply lift off the gas and coast. Perfect this kind of driving and your mpg will go WAY up.

I always beat the EPA estimates, with every car I've owned. I'm currently driving a 2002 4Runner Sport, auto, 164k miles. Owned it about a year, and the previous owner did nothing to it. So I'm working through all the maintenance. It's stock, on normal street tires, and I get 16ish around town, and 22ish highway. That's cruising at 65mph. My wild guess is 55 - 60mph is the sweet spot for these trucks. Every mph above that reduces your gas mileage, so I'm assuming you guys who barely get above 20mpg highway are hitting 70+.

If you NEVER go above 2k RPM, your MPGs will thank you

That's not entirely true. Gas engines are generally more efficient at higher throttle levels. The problem is if you're a "drive it like you stole it" kind of person that usually comes with speeding and a lot of gas-brake-gas-brake-etc... type driving. It's the brakes that are the problem, not the gas. You can accelerate briskly all you want, as long as you don't speed to the point where you have to slam on the brakes all the time.

I used to be a grandpa like driver, but I have noticed that slow acceleration doesn't really net me any improved gas mileage. Now I use as much gas as I feel like, and while I don't floor it I'm not easy on it either. The key is I get off it and coast once I hit the speed I'm looking for, which in town might be 35 - 40mph, or less. I used to annoy other drivers with how slow I accelerated, since abandoning that approach I have not noticed any decrease in mpg.

 

[St Runner]

I think the terrain you drive and how hard you drive are the biggest factors. That is the biggest reason the ect gets better milage for some but not others. The ect is a non factor on highway driving and effective in steep terrain. I feel the 3.4 runs best in the 2-2.5k rpm range (the 2.7 about 500 rpm higher) and when I had the auto in, even with the ect on it would upshift at a lower rpm than what I wanted. Thankfully with the 5 speed I can tell my 4runner when to shift and not rely on a 20 year old computer that was not designed for the roads I drive. OP I would replace the front AF/O2 sensor if you have more than 150k miles, it is the only thing left that can really effect your mpg

 

[mckennar]

I had a long trope written about a series of anecdotes relating to fuel economy, but the moral of the story here is that different drivers will get different mileage on the same route in the same vehicle.

Do you always need to be the first across the intersection at stoplights? Do you regularly rock the air conditioning even when it isn't needed? Do you have wider tires? How are your tire pressures? What's your altitude? Blend of fuel? Brand of fuel? Octane? Hills? Traffic density? Etc, etc. My point is, there are a bunch of variables to consider, but if you take the same route with the same driver and the same vehicle for a long enough time, the outliers created by those variables tend to work themselves into the average.

 

[Rock_Rat]

All above comments are spot on. Just a perspective on mine. When I was stock I was getting close to 19 -21 on average with rpm's around 2100. Once I started doing the mods it dropped around the 17 -19 range. Now with the 285's on 17" wheels all the external armor, rack, 4.88's and a brand new exhaust with new sensors ISR and deck plate I've dropped to around 15.7. My RPM's hover around 27-2800. I use Exxon gas which has been pretty good for me.

My gas mileage takes a huge hit because of where I live. Once I'm off the freeway my drive home is 3 miles straight up without a break in elevation. I'm not complaining.

Here's the motto I've always heard. If you want good gas mileage, you need to drive as if you have an egg under your gas pedal.

 

[kiana]

Our generation 4Runner's and correlation to gas mileage is hugely dependent on how hilly the area is. I got 21 MPG on a 70mph highway run for about 1 hour back and forth but this highway is pretty much COMPLETELY flat.

Around where I live in Nashville about 70% highway/30% city I get no better than 16MPG. And for most members on this forum, 15-16MPG is what you're gonna be dealing with.

 

[DJ_VanMeter]

I just bought a stock 02 4x4 automatic with 265 m/t's on it and I am getting around 16-17 mpg average. My drive to work is about 10 miles, half freeway. I wasn't super stoked about the mileage seeing people on this forums claim you can get up to 19+ on a maintained and well driven 4runner.

Since buying, I have done seafood treatment, plugs /wires, cleaned tb, cleaned mas, new air filter( paper filter not oem), and will be doing the fuel filter soon. I'm pretty sure there was almost zero maintenance done to this stallion because the air filter alone was holding what seemed like pounds of dirt. I think the plugs were original, the shocks look to be original, lots of little things I'm now noticing. But I'm hoping the above mentioned will help out and will be going through the driveshafts and regreasing all fittings next week or two. Still have my fingers crossed to achieve 18 mpg.

Would old saggy (about 1 inch from oem height) suspension contribute to bad mpg as well?

 

[jeremyc74]

Can't help but think the #2 O2 sensor (behind cat) might be getting old and giving weak readings, etc. No engine codes, though. Just a guess but I've got nothing left to imagine what is making the difference.

PS: Are EPA mileage estimates done on flat ground?

Just FYI, it's the forward O2 sensor that matters. The second sensor is just there to make sure the cat is working properly. The engine isn't doing any fuel trims based on that reading.

 

[Dhowl513]

"For better mileage, adjust the nut behind the wheel"

In all seriousness, like stated I think mileage you get will depend on a lot of factors, vehicles mechanical condition and your driving habits... This is why it probably varies so much. I get anywhere from 13-16mpg city driving and 19-21mpg highway depending on speed...

:bravo:

 

[mckennar]

Since buying, I have done seafood treatment...

mmmmmm lobster.

Edit: to be slightly more helpful towards your question - saggy *front* suspension might actually help. Take a look at the way new Silverados come from the factory - all of this plastic cladding on the bumper gives it a crap approach angle and makes it look dopey... but in a new Silverado, that air dam and lowering of the *front* (combined with active fuel management) gives them the ability to hit 25 MPG on the highway.

Now, in our trucks, sagging suspension usually means rear, which might hurt slightly as the underside isn't exactly flat though I don't have any experience with that. Mine got the same mileage pre-99 talls and post 99 talls install.

 

[DJ_VanMeter]

Yeah 4runners love turf and surf. Someone sticky that somewhere lol. Makes sense a lower front end stance could help mpg, I'm more worried about suspension not absorbing the road like it should taking away from mpgs.