Another poor fuel mileage problem
 

Quick question, I have a 1987 22ret 4x4. The problem is, my gas mileage sucks for the last 3 months. I am using a quarter tank going 44 miles. My truck has 177000 miles, has 33” tires, 2 ¼ inch exhaust with hi flow cat. 2 months ago I changed all the spark plugs, wires, cap and rotor as well as timed the engine with the jumper wire bypassing the computer, changed the 02 sensor even though there was no code thrown, ran a can of seafoam through the fuel tank and a couple of caps of Seafoam through the intake, I also changed out the PCV. Could an old fuel filter be causing this or is there anything else that I may be missing that could still be causing me to get about 120 to 150 miles on a full tank? I have done multiple searches on Yota tech on this and I find MAF, MFA, MSA, MAS, can't remember which, but it does say to clean it. First of all, can somebody explain to me what the abbreviation is for and second point me in the direction on how to clean or repair these.
Regarding the 33” tires I did compensate the mileage, I figure for every 10 miles on the odometer I should be traveling aprox 12.5 miles, I think.
Again, thanks for the help.
JMach1

did you regear when you got 33s?

No, still the stock gears.

thats proabably it then.

when my truck is running right with my 22re and 33's stock gearing, id still get 200-250 miles on a tank, almost got 300 once (actually is more due to the tripmeter still calabrated for smaller tires)

MAF is the Mass Air Flow meter, but thats on 2RZ-FE, 3RZ-FE, 5VZ-FE AND 1FZ-FE engines. What we have on the 22re's is called a VAF meter or Volume Air Flow meter. This is located on the top of the air box. You can test this with a ohm meter to see if its still good or not.

I would love to agree with ya, maybe talk the wife into letting me change the gears and add some lockers, but I have had the 33's on for a year after I installed the Chaos front end. This problem is about 3 months old as I was getting good fuel mileage prior to 3 months ago.

what were you getting in MPG 3 months ago and now? The cold weather takes a toll on MPG

EWAYota, thanks, Is this VAF meter a pain to work on or diagnose? I will search this sight and try to find a write up on it.

I was averaging probably 200-230 miles a tank. To tell you the truth I have never really paid attn to how many gallons are in the tank, I think its a 15 gallon tank. Right now about 6 miles a gallon and prior probably 15 miles per gallon. Ugh that sucks.

http://i11.photobucket.com/albums/a174/ewayota/VAF1.jpg
thats your VFM. to test it, disconnect the wire harness shown in the picture. taking a ohm meter, measure the resistance between terminals E2 and VS. Resistance should be 200-400 ohms.

quick idea of the terminals when looking at it from left to right will be FC, E1, VC, E2, VS, THA. So you want to check the 5th and 6th terminals.

to replace it, its just a matter of undoing the wire harness, and unbolting the old and rebolting the new and reconnecting the wire harness.

I appreciate this, now if the resistance is not between 200-400 ohms, maybe higher or lower, what does this mean, replace, clean or get a newer toy? HeHe.

replace it, i dont know if you can clean it or rebuild it.

the tank is 17.2 gallons, unless you have a long wheelbase truck then its like 19ish.

Don't forget that you're odometer is off by quite a bit with those 33s so you'll want to compensate or you're mileage will seem even worse than it really is.


But I'd correct you're data and see how much it improves, it may not be as drastic as it seems and is just a combination of the cold weather and the 33s that is causing it.

Thanks for all of the info guys. Now the real big question. When I bought the truck from my neighbor, he was a freak at maintaining this vehicle. But I do not know if he ever changed out the fuel filter, could this possibly be the problem as well?

could be, I had trouble starting, and not as much power before i changed my fuel filter

BTW: i came up with 17.8% for the difference you're 33s make on the mileage. So add 17.8% of youre miles per tank to the total and then divide by the gallons you put in. I'm sure you know how all that works...

could be, they're cheap enough to just go get one and swap it out anyways.

they may be cheap, but they sure are a pain to get to.

Have you checked the basics - tire pressure and alignment? Cold weather reduces the tire pressures, the "winter blend" fuels in most parts doesn't burn as efficent, so the combo could drop off the 20% difference you're seeing. Also have you checked the air filter? Plus - what weight of engine oil are you using? The trans/transfer/gear oil is going to be like goo when cold so that's resistance you didn't have in the summer. Remember too that idling is burning fuel without adding miles so limit the warm-up time to only a minute or so then start driving gently until the rest of the drivetrain gets up to temp.

17.8% difference.....dam.... i only figured going from 31" to 32" on my truck worked out to about 4%....did i do my calculation wrong or something???

Does the VAF actually affect mileage??

I would have thought replacing the O2 sensor would have got it.

17.8% would be going from stock 28s (225r15) to 33s.
31 to 32 is indeed 4%.