Losing fuel mileage

[e40gutierrez]

So I bought my 2003 QX4 in September, and normally I would get about 250 miles to the tank
and 3 weeks ago I started getting about 160 miles to the tank. I replaced my sending unit because it was bad, also I did a tune up on it, and still getting s*** mileage. I have no clue what would make my mileage drop about 90 miles. I'm not leaking gas, the truck has 142k, and runs great, no sputtering. I'm thinking maybe my oxygen sensors are bad? Or the fuel filter? Any one have a clue? I would appreciate the help.

[Pathy415]

I don't think it would be a bad fuel filter since you're still using up the fuel and your gauge is operating normally I assume? It could be a bad sensor or if your air filter/intake assembly is somehow clogged. Such a quick and sudden decline in mileage would make me think it might be the latter.

Lots of critters like the warmth of the engine bay after being driven so don't be surprised if you find something in the intake, it's not unheard of, or, it could simply be debris that has clogged the filter.

[Chris.m]

Wow, even the mileage that you started with its pretty bad, I do about 350 and up miles per tank (driving like an old man with 94 octane).

As far as I know, the fuel filter does not affect mileage, just performance. A dirty one may restrict the flow but the computer compensates for that. Similarily, a dirty air filter would too only hamper performance not mileage for similar reasons as the fuel filter.

Any lights?
you said you did tune up, so I'll asume you changed oil and transmission fluid and filters?
I have heard that oxygen sensors can go bad without turning on the SES light, but replacing them would be a shot in the dark...


-thats off the top of my head

Chris

[asnorton44]

Have you cleaned the MAF?

[Towncivilian]

350 miles?? I get about 260 if I drive to empty. No CEL, recent oil & filter, transmission fluid, power steering fluid, spark plugs, clean air filter and MAF, recent fuel filter... mileage didn't improve one bit.

But yeah, I'm echoing the suggestion to try cleaning the MAF sensor.

[Chris.m]

When I say 350 miles per tank, I'm doing the math for the tank, I find when people compare "going to empty", its a bit ambiguous.

I get on average 12-14 Liters/100km or 7.7 km/liter. Our tanks are 79 Liters,

7.7 * 79 = 608 km = 380 miles and to allow for error -> 350miles

I've replaced oil, transmission fluid, fuel filter, air filter,

inflate tires to 40PSI, took off roof rack and spare tire,

rarely go above 2500RPM

And recently switched to 94 octane

Also bought a scangauge which indicates (via a surprsingly accurate mileage computer) the best way to drive and cruise

-Just don't wan't you guys to think I like to make up fuel consumption figures to feel special...

[Densetsu]

I get around 7.5km/l in the summer with mixed driving, but didn't go as far as overinflating tires or removing excess weight, so I can say that a 7.7km/l tank is very much achievable. I only get this mileage with premium, though, since a lot of stations dilute their regular and mid-grade gas with ethanol.

My record was a bit over 9km/l, around 450 miles a tank. Granted, that was all highway and all downhill, from Banff on my way home to Edmonton (e.g. from mountains to prairies).

[coledog188]

I hammer on my Q...A lot lol. In the winter with auto engaged for 90% of the driving I'll get about 220-250 miles per fill up. Or about 14-16mpg...
Summer cruising at 70 down the interstate I get 19mpg though.

[e40gutierrez]

Do you think that a bad catalytic converter could give me bad gas mileage?

[Iceman2989]

Ive got a 97 pathy thats getting terrible mileage as well. Ditto on the catalytic converter question. I know mines no good..