mwc0404

So my mpg isnt great but ive noticed when i hit higher rpm my mpg gets worse, my cel is on and diagnostics points to a bad forward o2 sensor. Will the bad o2 sensor cause bad mpg at higher rpm or just worse mpg altogether?
Also on a different note, when i first start the 4runner after sitting for a couple hour or overnight as it goes through the gears the first time it winds each gear out further than it should then after the time through the gears its normal, it doesnt shift hard or anything it just winds out the gears the first time through. I had the trans drained and filled and the trans filter changed a couple of weeks ago and it stopped doing it for about two days after then started again, any thoughts suggestions or ideas?
oh and a side note to that is that there is no issue with power at all.

sleeper2002

sure a bad upstream O2 sensor could cause poor MPG. Anyone correct me if I'm wrong, but I think the ECU uses the info from that O2 sensor to help determine AFR. As for the tranny issue, I'm kinda stuck. Almost sounds like something in the valve body has worn to the point where when it's cold, it looses tolerance but when it heats up it expands and gains the propper tolerance. Just a guess.

mwc0404

im going to change the o2 sensor soon and see if that helps, but your suppose to get better mpg on the highway/interstate then backroads but due to low rpms on backroads and higher rpms on highway/interstate i get somewhat better mpg on backroads then on the highway, im talkin 2k rpms or more and my mpg goes to crap.

sleeper2002

Have you tried cleaning your MAF and scrubbing down yoru throttle body? Also, when was the last time you changed your plugs

mwc0404

that would be a no, no, and i dont remember! but now that im thinking about it it i'll get on that in the morning.

sleeper2002

Yea those would be a good things to do. I noticed a big difference when I did all three of those today. I'll have to get aback to you when I have time to calculate the milage.

mwc0404

do that and ill let ya know what i find when i get it done.

scuba

How do you know your MPG's are bad when your strictly over 2K RPM?
Yes. A bad 02 sensor will cause bad MPG's. Duh, losing.


And the transmission issue, its the 4Runners own personal way of warming up the transmission fluid.
Normal. Get used to it.

sleeper2002

Lol. Well there you go, just warm that puppy up!

85gijunk4x4

well...of course your mpg worsens as rpm's go up.

but an 02 would cause poor mpgs (well lower then expected) through all rpm's.

mwc0404

Well as for knowing the difference between over 2k and under 2k i did an extensive test where i only drove it to and from work and back for a while and used another vehicle for anything else and for a period of time i drove on backroads that run parallel to the interstate and for an equal amount of time drove strictly interstate and thats how i came up with the difference.

As far as the trans im just not used to that being normal because as long as ive had the 4runner it never did that until recently in the last couple of months.

mwc0404

hopefully changing out the o2 sensor will make that big difference in mpg that ive noticed lately

dmwahl

Higher RPMs usually means worse mileage, read up on specific fuel consumption for more info. Basically it has to do with all the different efficiency losses and finding the spot where they add up to the least. The graph they show in the wikipedia article is just an example.

http://en.wikipedia.org/wiki/Brake_s...el_consumption

Fink

As scuba already said, the O2 sensor will definitely cause worse mileage.

Also as scuba said, the delayed shift points is Toyota's way of warming everything up. Not sure what would cause it to be more obvious now, but I can tell you that it has done at least something similar since it was built. A way of testing it would be to start the Runner about 5-10 minutes before you leave and let it warm up on its own...if it doesn't do it after that, case closed.

FWIW, my 2nd (3VZ) and 3rd gen (5VZ) both did it.

Fink

mwc0404

thanks yall, changing plugs and cleaning the maf and throttle body now hopefully it helps, ill be changing the o2 sensor as soon as it arrives. I'll let yall know how she runs after the plugs and cleaning are done.

Fink

That's a good start - the more little things you can do the better.

Replacing the fuel filter and cleaning the TB is probably a good idea also.

Fink

mwc0404

ok ran into a problem, i changed the plugs on the driver side and moved to the passenger side, took off the intake hose and removed the first coil and the boot broke off inside around the plug, anybody know where i can get a new boot and any ideas on how to get the rest out so i can get to the plug?

Fink

Pics??

Fink

mwc0404

whew, ok solved it. i used a lond flat head screwdriver to break the remaining piece of boot away from the plug and a looong pair of needle nose to remove it. after i removed the spark plug i found that the boot had melted to the plug slightly and thats what caused it to break. went and picked up a new boot from autozone for 20 bucks, now to go put it in.

Texas_Ace

You made darn sure that none of that boot went into the engine right?

You are on the right track with the tune up.

Yes the O2 sensor will cause the truck to not run as well and cause a loss of gas mileage for sure.

Yes the tranny "issue" is normal.

Far as getting better gas mileage on the highway, it depends on what speed you are driving. These trucks are basically driving bricks so if you are speeding at 70mph+ yeah gas mileage will drop. But if driving the speedlimit you should get better gas mileage.