Losing gas mileage; HELP!

Reid Roeske · 12-11-2007, 12:47 PM

Hi all, I have a 2004 Titan, w big tow, and off road packages. I had been getting 14 - 15 mph until about 3 mths ago, then it started to drop to around 11 on the highway, with the recent low of 8.6! It's been to the dealer twice, first time they said the air flow sensor needed an "update" which they did. No change, second time they see nothing wrong on teh computer. I have changed teh air filter (k/N), air pressure in the tire @ 40 lbs, and have changed the oil. The dealer doesn't know what to do, and neither do I. It's getting to the point where I might have to get rid of it.

Has anyone run into this, and more important, any solutions? I'll try anything, I like the truck, and don't want to get rid of it. Thanks!

saltydog · 12-11-2007, 12:51 PM

i guessing that it's the winter fuel

cneary812 · 12-11-2007, 12:52 PM

have you changed gas stations lately? I know that mine is very picky about what types of gas I put in. Or maybe your station switched to more ethanol. 11 on the highway is really not normal unless its really cold and you have one heck of a headwind while traveling at 90+ miles per hour in 4wd with 35" mud tires

good luck

Skyboi · 12-11-2007, 01:25 PM

Maybe I'm wrong but.....When you switch to the K&N filter, the filter channels more O2 to the engine. Subsequently the oxygen sensor senses the extra O2 and compensates by increasing the amount of fuel to compensate. therefore dropping the mpg but increasing the horsepower.

I was going to do the same thing for the increased power but a tech friend explained it to me and I decided that my power is fine...I need the mpg right now....try switching the filter back and do another mileage check....good luck

cneary812 · 12-11-2007, 01:28 PM

Quote:

Originally Posted by Skyboi

Maybe I'm wrong but.....When you switch to the K&N filter, the filter channels more O2 to the engine. Subsequently the oxygen sensor senses the extra O2 and compensates my increasing the amount of fuel to compensate. therefore dropping the mpg but increasing the horsepower.

I was going to do the same thing for the increased power but a tech friend explained it to me and I decided that my power is fine...I need the mpg right now....try switching the filter back and do another mileage check....good luck

Its not the k&n filter doing it. Mine improved my overall mileage a bit

Clint · 12-11-2007, 01:57 PM

Quote:

Originally Posted by saltydog

i guessing that it's the winter fuel

I agree with the winter fuel theory as I always reset the trip counter and need gas way earlier than in the warm weather. Close to 40 miles less per tank. Isn't it great they raise the price and we get less energy from the gas.

Clint

**Kronos1965** · 12-11-2007, 02:04 PM

The system does take time to learn new a/f mixtures. That happened with my K/N.

I wonder what would happen if you put in octane boost?

Clint · 12-11-2007, 02:27 PM

Octane boost cost too much to consider using. Add its cost to a tank of gas then divide by gallons bought to see the new cost per gallon for fuel.

Clint

37L1 · 12-11-2007, 02:32 PM

Quote:

Originally Posted by Reid Roeske

Hi all, I have a 2004 Titan, w big tow, and off road packages. I had been getting 14 - 15 mph until about 3 mths ago, then it started to drop to around 11 on the highway, with the recent low of 8.6! It's been to the dealer twice, first time they said the air flow sensor needed an "update" which they did. No change, second time they see nothing wrong on teh computer. I have changed teh air filter (k/N), air pressure in the tire @ 40 lbs, and have changed the oil. The dealer doesn't know what to do, and neither do I. It's getting to the point where I might have to get rid of it.

Has anyone run into this, and more important, any solutions? I'll try anything, I like the truck, and don't want to get rid of it. Thanks!

Try resetting the ECU?

How to:ECU Reset,Throttle & Accelerator Position Learning

**anmut** · 12-11-2007, 03:36 PM

Quote:

Originally Posted by 37L1

Try resetting the ECU?

How to:ECU Reset,Throttle & Accelerator Position Learning

I was told resetting by disconnecting the battery will kill any timing advance on the 2008.

37L1 · 12-11-2007, 03:52 PM

Quote:

Originally Posted by anmut

I was told resetting by disconnecting the battery will kill any timing advance on the 2008.

This isn't disconnecting the battery and there is a matter of opinion about that.

Reid Roeske · 12-11-2007, 07:28 PM

Thanks for the replies so far. In answer to some of teh questions..
1. I have not switched gas stations, and I noticed this problem in Sept, I assume way too early for "winter gas"

2. I switched to the k/n filter after I noticed the mileage falling

3. I tried resetting the ecu about 2 months ago (from this forum)

It has been mentioned to me that a bad fuel filter may be the cause. I was told there may be two filters, one being a return? Thanks again for the brainstorming.

*yourpapi* · 12-11-2007, 08:19 PM

change your spark plugs... that could be the cause...

HudsonValleyTitan · 12-11-2007, 09:25 PM

Where do you live? If you're in the NE states, there is no winter gas anymore. It's all 10% blend. I'd try a stock air filter if that's all you've changed. 105k plugs so...they should be fine. 8.6 MPG without towing ? I'd say there's definitely a problem. My 04 is closer to 13-15 around town with no upgrades or updates to the ECU or any sensors. An 02 sensor on the way out maybe?....no idea.

cneary812 · 12-12-2007, 07:18 AM

another thought. Have you checked to see if you have a sticking brake caliper or parking brake? The other obvious stuff I left out because you said in your first post that you took it in 2 times to the dealer. If the tech has half a brain he would have checked those things out already (fuel filter, injectors, tires, brakes, MAF, etc) but we all know that most of them dont have half a brain so you may want to dump a can of complete fuel system cleaner in the next tank to see if that helps.