terrible gas mileage 3.4L v6

I somewhat recently got a 2000 SR5 xtracab 4X4, and although it runs great my mileage is, like yours, terrible. 11 or 12 mpg.

But I drive exclusively in a very hilly city, stop and go, rarely getting up to even 35 mph. With big stupid tires, too.

 

What kind of tires? Are they C rated or E rated?
What kind of filter did you replace it with? I'd stay OEM or AFE pro dry (no oiled filter, it will dirty the MAF)

If you haven't already, keep under 2k rpm.

x2 on new OEM spark plugs

Clean your MAF again, including down into the stem.

Try using name brand gasoline if you haven't already.

I think those are the biggest things. Everything else I can think would only make relatively small differences.

I'd assume you'd already have done an oil change.

Next I'd look at a professional fuel system and intake cleaning. Find a shop that offers "motorvac" service. I did this at ~100k mi and noticed a very slight gain in mpg. Or try that

$24 BG 44k Fuel System Cleaner Power Enhancer 11oz.

BG 44k stuff everyone loves. Seafoam makes a lot of smoke but, I personally didn't notice any difference.

Personally I can get as high as 19-20mpg highway (60mph cruise control) and about 15mpg city. Double cab with c grade duratracs (which are heavier than the BFG all terrains that came with it)
In the winter I get about 13-14mpg highway/city mixed.

 

it seams to be idling rough more often now and idles around 600rpm (hard to tell exactly) when it idles rough and then will go up to 750 and idle smooth after a while. seams like after its been on the road its fine but first start up hot or cold it seams to idle rough.

will have to run some fuel system cleaner through it but until I get those plugs changed I cant tell if what im doing is doing any good

 

Agreed.

I'd go 60mph on highway. 10mph is a small difference that will have a noticeable effect on mpg.

What tires and what load rating are they?

 

Michelin 265/70/16 http://www.walmart.com/ip/LTX-M-S2/12521601

if I do 60 mph I will be run off the road or cause accidents. speed limit here is 70mph and cars do 80mph normally so im in the slow lane doing 70mph just to stay outta trouble and not get run over

 

I understand. Personally I just stay in the right most lane. Mainly 3 lane highways so its easier to do. Anyway, yeah those tires are avg weight and road-use tread style. Don't think the tires could be a cause. (it is for me)

Spark plugs and fuel system cleaner, like you said. I'd just disconnect the battery to reset the comp after you change the plugs, give it a couple tanks to average out and take it from there. That motorvac is a pressurized system. Seemed more effective than a bottled cleaner.

 

Yea try some injector cleaner and gas treatment by stp it's what I use along with octane Booster. You might not notice a difference at first but it'll work.

My 3.4 was idling rough and I ran injector cleaner through 2 fill ups (usually around a 1/3 tank) and I noticed a big difference after 20-30 miles on the first tank but ran it through 2 tanks just to be sure.

 

When I recently changed my plugs, they were worn on both sides evenly, it is the center electrode that burns off.

 

The 3.4 fires each plug once every revolution, 2 plugs at a time. This is twice that of more conventional systems hence the extra electrode. It's for plug life, nothing else and that "life" will be roughly double that of a single electrode.
For each coil, one plug fires from center to ground and the other ground to center.

 

ok so if I say went to single electrode then the plug life would be half that of the originals then.

interesting, I did not know that.

do you think it does any good to replace the plug wires "just for the hell of it" because they are originals with 115k miles or wait until I suspect there might be a problem with them?

 

This isnt going to be a issue with your current truck of course, but i wanted to toss this in. I used to have a 94 ranger and it got about the same mileage as what you are saying for the first two tanks at least. But i got a bed cover for it, just one of the cheap snap on kind, picked it up off craigslist for $100, i got it so i could store things in the bed without people having the convenience of look and take, now it would at least make them unsnap it or drop the gate to see what was in it.

Then i discovered that it had a big side benefit, better gas mileage, it gave me a near 4-5mpg difference between running a tank with it on vs with it off and rolled up near the cab rear window.

Your results of course might vary, but at least that particular time, i got a good gain from it. but as that was the only time i have had a truck and a cover, i cant say if it would work like that every single time.

 

How do you reset the computer?? Just curious.

 

I have a K&N air filter, I get around 340 miles a tank at avg 20 mpg. Mostly Hwy driving. Ive seen a 1-2+ improvement

 

I just disconnected the battery for 10 minutes. Just don't do this before a smog check (if your in California) this will be an immediate fail.

After connecting the battery you will need to meet some driving conditions before it's fully programmed on your driving habits.

 

under the hood the fuse box there has a black box fuse that is labeled EFI and that's the one that resets the ECM.

unplug it for about 10-15 minutes is all it takes but I usually let it go 30 just to be sure.

if you unplug the battery it does the same thing but you have to reset the radio stations and clock.

 

4 cylinders are much different, my 99 with the 2.4 engine I put the aftermarket filter in and upgraded to 4 hole injectors and it got 21 city and 25 highway but the v6 is a whole different animal you cant compare the I4 to.

 

Any updates?

How many miles do you have? I forgot to mention this link:
http://www.4x4wire.com/toyota/4Runner/tech/O2_Sensor/
It cites that a check engine light doesn't necessarily have to be on to have problems

 

If you look at my sig I avg around 16mpg. If I air up the tires (40 PSi) I get better. ride is a little stiffer but I dun care. I have hills and all around here so I can only get to about 18 in PA but the most I ever got was 21 in my trip to NC (368 miles for 17.x gal)

also did you grease all zerks with the good stuff? I noticed this also helps with lessening axle wrap as it allows the slip shaft to move freely.

and for that 2nd tank you might have reset the trip early on and just didn't realize

 

I find that by driving at 70-75 mph I get slightly better mileage. Sounds counter intuitive I know,
but something about the gearing and power band my 3400 has may have a bit to do with that. Seems easier for the truck to maintain that speed.

 

oh ya, forgot to mention that was at 75 mph, thanks for reminding me