poor MPG

[Custom88]

Ok, starting to get a little annoyed here because it's mid January, and I'm only getting 22 MPG average here.. I know, most will think that's not a big deal. However, Just back in September I was averaging OVER 28 MPG in the same driving conditions. I keep a log of my gas mileage at each fillup and this is how it breaks down.

August 26.98795181
September 27.20720721
30.6372549
24.70288625
25.4676259
24.41742655
24.13335545
24.32835821
24.12451362
December 24.21052632
22.57045205
22.19909816
January 21.17283951

I haven't reset the average MPG on my DIC since September and since then, it has gone from 28.7 MPG down to 22.7 average.. I used to get 41 MPG instant at 55 MPH, now I get anywhere from 25-27 MPG instant at 55.. I used regular 87 octane all that time, and now switched back to 93 to see if it made a difference.. It has not.

This same time last year I was also getting 25.6 average, and it was a MUCH colder winter last year! Ideas? I have 52,000 miles BTW. The transmission locks into overdrive like it should, and there aren't any error codes...

[skexius]

custom88 said:

Ok, starting to get a little annoyed here because it's mid January, and I'm only getting 22 MPG average here.. I know, most will think that's not a big deal. However, Just back in September I was averaging OVER 28 MPG in the same driving conditions. I keep a log of my gas mileage at each fillup and this is how it breaks down.

August 26.98795181
September 27.20720721
30.6372549
24.70288625
25.4676259
24.41742655
24.13335545
24.32835821
24.12451362
December 24.21052632
22.57045205
22.19909816
January 21.17283951

I haven't reset the average MPG on my DIC since September and since then, it has gone from 28.7 MPG down to 22.7 average.. I used to get 41 MPG instant at 55 MPH, now I get anywhere from 25-27 MPG instant at 55.. I used regular 87 octane all that time, and now switched back to 93 to see if it made a difference.. It has not.

This same time last year I was also getting 25.6 average, and it was a MUCH colder winter last year! Ideas? I have 52,000 miles BTW. The transmission locks into overdrive like it should, and there aren't any error codes...

Custom88,

Do you think that the reduction in fuel economy could be because of the oxygenated gasoline that the northern states switch over to in the winter months to reduce ozone and harmful emmissions from automobiles?

Just a thought!

skexius

[TJM]

tire pressure? air filter? blended fuels? are you driving with your doors open? JK

tire pressure can be a huge factor and one that is often neglected and not addressed for cold air. Just a thought.

[BNICOV]

Winter Gas is a bit different from summer gas, as well, are you warming your car up for a minute or two when you are starting it up now?? Tire pressure should be checked although the tire pressure monitor should pick that up if you drop into the low 20Psi range. Also, a clogged air filter can contribute. I have noticed a drop in my mileage lately as well but I attribute it to running the car for a minute before I drive off.

[BNICOV]

Oh yeah, you have a K&N filter, make sure you don't put too much oil in it. That stuff can reek havoc with your throttle body and sensors along the way.

[Custom88]

tire pressure is 33 PSI in all three tires and my air filter is only about 4 months old. I let my car warm up for around 1-2 minutes before taking off usually. I'm doing everything the same as I did a year ago.

[95rora]

How about wind? With trees having no leaves and such it doesnt get blocked on the highways as bad. It seems like everytime I drive somewhere the wind is blowing like crazy. I know these cars dont feel it very much, but it makes a tremendous impact on mpg. Im averaging 20 instead of the 24 or 25 that i normally get.

Also, reset your AVE/MPG and see what you get for one tank. Otherwise its doing an average over the last three or four months and isnt quite as accurate of a gauge.

[Aurora40]

custom88 said:

I let my car warm up for around 1-2 minutes before taking off usually.

Don't do this then. Just take off gently until the car warms up.

Also, does the pump agree with the DIC? Not resetting the DIC probably isn't the way to get accurate metrics.

Your car does have a few changes since last winter, right? One is the spoiler, which will drag (though I wouldn't think a lot), and the mufflers which I'd think would slightly increase economy. Are you sure you are driving the car the same? Do you ever keep the car on instant MPG to try to maximize it?

[MBowen574]

I've been struggling with fuel economy in my Galant. It's a 2.4L four-cylinder with only 141 hp, and I used to average 18-20 mpg (when I watched it... I once got a 2-tank average of 16 mpg!). I've done tons of things to the car, as suggested by various sources (Haynes manual, The Galant Center forums, etc.). I'm now getting 23-24 in average (not light) city driving, so it's improved quite a bit. I ran Lucas Oil brand injector cleaner in it (about $11 at Advance and NAPA for a 30+ ounce bottle, and you only use around 4 ounces per fillup until the whole bottle's gone) and cleaned the [very, very dirty] throttle body. I also changed out the fuel filter, which I wouldn't think would have much of a big effect, and also yours shouldn't need changing. However, after each of those changes, my mileage went up between 1 and 2 mpg. Also, are your tires nearly worn? I hear that can have a surprisingly large (like, 5-10%) effect on mileage. Just some thoughts.

BTW, you V6'ers are generally pretty lucky. Our 4.0 hangs right around 15 mpg in city driving and 18-21 on the highway.

[erw38]

custom88 said:

tire pressure is 33 PSI in all three tires

three tires? You must have done some major mods ;D

[Custom88]

aurora40 said:

custom88 said:

I let my car warm up for around 1-2 minutes before taking off usually.

Don't do this then. Just take off gently until the car warms up.

Also, does the pump agree with the DIC? Not resetting the DIC probably isn't the way to get accurate metrics.

Your car does have a few changes since last winter, right? One is the spoiler, which will drag (though I wouldn't think a lot), and the mufflers which I'd think would slightly increase economy. Are you sure you are driving the car the same? Do you ever keep the car on instant MPG to try to maximize it?

lets not forget about the intake either.

The gas pump agrees almost completely with the DIC. My gallons used for example said I used 9.9 this tank of gas, and I pumped exactly 10.0 gallons into it to fill it up. The pump said I got 23.2 MPG (calculating it myself manually) and the car still said 24.4 or so. I reset the DIC average gas mileage today and I'll let ya'll know what it reads after a week. So far from driving today it's reading 26.1 average. This was with the engine already fully warmed up and backroad driving at 55 MPH.

three tires? You must have done some major mods ;D

d'oh. That's what I get for posting when I just get up. lol. I didn't even catch that! ;D

[Wacko]

Carrying around any extra weight? In the trunk? Of the car? Dead bodies, etc.

I noticed that I was getting about 22.8 MPG all autumn long. Then, it started dropping and has settled at 21.7. This is nearly all backroads driving. Come to think about it, I have switched gas stations. Hmmm. Perhaps lowest price is not always the best buy.

I switched from Exxon to this guy, US Gas, because he is always $0.05 less per gallon. Time for an experiment. I'm switching back to Exxon for a month to see what happens.

[macadamiaman]

O2 sensors contribute a LOT to gas mileage, don't they? Perhaps at 52k if they were never replaced, try that. Didn't steven get a huge improvement?

Anyway I've always had horrible mileage, mostly highway driving in the winter I average 18-20mpg, summer 22-24mpg.

[stevensolds]

My MPG wente up by over 100 miles for tank. Im not joking or exaggerating it either. I got 346 miles out of the last tank (i actually fill tanksn ow) and before it was always under 200 miles, even with the same driving! I let my car warm up for 4-5 minutes too. If you just start it up and drive off in negative temperatures like Dan lives in, your engine wont live as long as it should. Dont tell me its not hurting anything either, I dont want to hear it. You arent flowing any oil at those temps, and imagine the piston going up and down with no lubrciation..but having Mobil 1 helps. 6k also is a bit too long I think, but whatever your preference.................

everyone I know starts the engine and immediately puts it into gear and drives away. I wont do it.. The cobra over here is a classic example. He not only starts it up, but he guns it. And he wonders why his engine had to be rebuilt after 100k miles....idiot.


So yeah dan try replacing those 4 oxygen sensors you have. That should be no more than a (measly) 300 dollars installed..

[Custom88]

The 3.5L only has two oxygen sensors. One in the exhaust manifold directly behind the engine(actually in the crossover pipe), and one after the catalytic converter. the one in the exhaust manifold is the only one that influences gas mileage.

[stevensolds]

Wouldnt hurt to replace both of them. Mine had 2 as well. Later year classics had 3 i believe, stupid emissions stuff.

[Aurora40]

stevensolds said:

If you just start it up and drive off in negative temperatures like Dan lives in, your engine wont live as long as it should. Dont tell me its not hurting anything either, I dont want to hear it. You arent flowing any oil at those temps, and imagine the piston going up and down with no lubrciation..but having Mobil 1 helps.

I'd be curious to know what your pistons do while it is idling in the cold then. Since apparently they don't go up and down during that time...

[95rora]

Dan, Im curious about one thing. How often do you run injector cleaner? Alot of times a good injector cleaning will help restore some lost fuel economy especially during the winter months. Sea Foam I was told is the best and you can get it at most any parts store. Try some of that before you buy some O2 sensors and see if it doesnt help somewhat.

[stevensolds]

Bob, I was impying it would be worse if you bring the revs over 1000.

[norbi]

My 4.0 gets about 14-16 city driving and on a highway when i am not speeding going about 70mph i get 29-31mpg on one trip to upstate NY which was 117miles i only used 3.7 gallons when my brother in law was following me with his 3.5 Aurora used same amount. But city driving my moms and his are killing my 4.0 in gas milage.

[GlennS87]

norbi said:

My 4.0 gets about 14-16 city driving and on a highway when i am not speeding going about 70mph i get 29-31mpg on one trip to upstate NY which was 117miles i only used 3.7 gallons when my brother in law was following me with his 3.5 Aurora used same amount. But city driving my moms and his are killing my 4.0 in gas milage.

I see the same results in the city with my 4.0 but my highway cruise (typically between 80-90mph) gets me about 23-24 mpg.

[Custom88]

My average is down to 23.1 MPG this year. This exact same time last year, I was getting 25.6 average, same driving route and everything. my instant MPG on the highway is way down too. Before I was getting 38 MPG @ 55 MPH, now I can't get anything over 29 instant at 55. I can't pinpoint what has changed. It could be the 02 like steven said, just haven't had the time or patience to do it yet.

[macadamiaman]

Mine sits at 22mpg...

This summer I suppose I'll get O2s done, 75k miles... I'll hit 100k before I know it, whatever...

[macadamiaman]

I am now down to 16-17mpg. Even coasting at 35mph downhill (maintaining speed in neutral), I am only getting about 60mpg.

Find a solution, 88?

[BNICOV]

Sounds like 02 sensors. Mind you, if your cat is toast, it would also cause your fuel economy to drop.
Good luck on figuring it out.

[Custom88]

I havne't figured anything out yet. still in the low 23 MPG range. haven't had time to take the car in either for all of the warranty work it needs.