Sudden loss in MPGs - TCCoA Forums
 
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post #1 of 13 (permalink) Old 01-06-2008, 12:38 AM Thread Starter
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Sudden loss in MPGs

My car has been doing pretty good on gas ever since I owned it but lately all of the sudden it has been averaging between 10-12 miles per gallon in the city. I used to get at least 16-17. It was a real sudden change.

What could have caused this so suddenly? I know the car needs new injectors but it has needed them for a couple years now. Also the MAF was replaced in the last two years and the air filter is pretty clean.


What should I check? Anyone else ever experience a sudden loss like this?

'96 Alpine Bird 281ci
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- Purchased with 36,000 miles, now at 101k
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post #2 of 13 (permalink) Old 01-06-2008, 01:09 AM
TGJ
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I have seen this happen often. Any big change in weather recently, did it just get colder outside? Right now my 5.0L 4x4 is getting 12 MPG in the city 18 MPG on the highway with the temperature +2 to -10 Celsius. When it gets to -20 outside, the mileage drops to around 7 MPG city and 12 MPG highway. That could explain it...

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post #3 of 13 (permalink) Old 01-06-2008, 01:22 AM Thread Starter
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Yeah, actually the temps have dropped dramatically this week. I thought about this being the reason, but I've had this car through 3 pretty cold winters and I have never seen this happen before....

'96 Alpine Bird 281ci
- Clear Corners
- DynoMax Cat-Back
- Purchased with 36,000 miles, now at 101k
- No mods planned untill it's DD life is over

1998 5.9 Limited Grand Cherokee
- Flowmaster Exhaust
- AEM Brute Force Intake
- Mopar Performance ECU

- 275hp-395ft/lbs at the crank (est.) Track results in the spring!!!
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post #4 of 13 (permalink) Old 01-06-2008, 11:43 AM
No, Mr. Lemmywinks, No!!!

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There's more air in the colder air, for one.

The other thing is the amount of ethanol they put in gas when it's cold; ethanol=bad mileage.

My winter gas dropped me about 6 mpg this year; that seems to be what you are seeing...

O2 sensors made the most difference in my mileage; old sensors suck.

Red '96 Cougar XR-7 240k mi. '02 4R70W, PST DS : '03 PI engine, 04 maf, 24lb injectors, 2.5" exhaust, '02 4r70w + Jmod, DirtyD0g TC + cooler + 3/8" lines, 255 walbro fp. Alpine system.
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post #5 of 13 (permalink) Old 01-06-2008, 01:57 PM
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Quote:
Originally Posted by Grog6 View Post
My winter gas dropped me about 6 mpg this year; that seems to be what you are seeing...
Same here. Didn't hit me as hard on the highway but in town . . . holy crap.

Between the cold air and winter fuel blend, my mileage (even with the 3/4 of an engine) tanks.

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post #6 of 13 (permalink) Old 01-06-2008, 05:15 PM
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Makes me wonder about the advantages of "oxygenated" gas. It's supposed to cause less pollution but then ....we burn more of it to go the same distance!!!

Bob
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post #7 of 13 (permalink) Old 01-06-2008, 05:25 PM
No, Mr. Lemmywinks, No!!!

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Same here. Didn't hit me as hard on the highway but in town . . . holy crap.
The energy per mile is lower on the highway, so the loss is less noticeable; in the city, every bit counts.

The biggest part of converting to E85 will be the huge gas tanks...or a daily fillup.

Red '96 Cougar XR-7 240k mi. '02 4R70W, PST DS : '03 PI engine, 04 maf, 24lb injectors, 2.5" exhaust, '02 4r70w + Jmod, DirtyD0g TC + cooler + 3/8" lines, 255 walbro fp. Alpine system.
Black '96 Cougar XR-7 (Lazarus) 210k mi PI Intake, '02 4R70W, Jmod, PST DS, GrogTune, Konis, Mark LCA+Poly, racecougar Custom Engine Chain, and JL and racecougar Bracing.
Black '97 Tbird Limited Edition, '02 4R70W, 255 walbro, PST DS, PBR Brakes&SS lines, Toicko Blues & Springs, GrogTune.


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post #8 of 13 (permalink) Old 01-06-2008, 06:19 PM
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which 02 sensors would be the most beneficial to fuel mileage...upstream or downstream?
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post #9 of 13 (permalink) Old 01-06-2008, 07:47 PM
No, Mr. Lemmywinks, No!!!

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The upstream sensors are the only ones that control the engine...

The others apparently only tell you that your cats are bad.

If the rear ones go really bad, they will bring down the whole system, tho.

"Sensor circuit error" or something like that...I don't remember the code.

I bought two new ones, and got ~+5mpg (22 to 28) last summer; you won't see that much on winter gas unless they're really bad...

Mine originally started throwing codes, and I replaced the front ones (fixed almost all the codes), and moved one of the old front ones to the rear position that was giving me issues, and no more hassle.

The gas mileage was a nice bonus!

You can turn off the rears with a tune.

Red '96 Cougar XR-7 240k mi. '02 4R70W, PST DS : '03 PI engine, 04 maf, 24lb injectors, 2.5" exhaust, '02 4r70w + Jmod, DirtyD0g TC + cooler + 3/8" lines, 255 walbro fp. Alpine system.
Black '96 Cougar XR-7 (Lazarus) 210k mi PI Intake, '02 4R70W, Jmod, PST DS, GrogTune, Konis, Mark LCA+Poly, racecougar Custom Engine Chain, and JL and racecougar Bracing.
Black '97 Tbird Limited Edition, '02 4R70W, 255 walbro, PST DS, PBR Brakes&SS lines, Toicko Blues & Springs, GrogTune.


"War Is Peace. Freedom Is Slavery. Ignorance Is Strength." - George Orwell.
Truth Isn't Truth. - Rudy Giuliani, 2018 Award winner, “Most Outrageous Diversion” by MSNBC for this quote
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post #10 of 13 (permalink) Old 01-06-2008, 09:22 PM
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sounds like typical 10% ethanal mix to me. try to find somewhere with regular gas.

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post #11 of 13 (permalink) Old 01-07-2008, 12:12 AM Thread Starter
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thanks guys, i am seeing that this is more then likely the problem. The temps reached about 50 F today and the mileage seemed to have gone a up a little.

'96 Alpine Bird 281ci
- Clear Corners
- DynoMax Cat-Back
- Purchased with 36,000 miles, now at 101k
- No mods planned untill it's DD life is over

1998 5.9 Limited Grand Cherokee
- Flowmaster Exhaust
- AEM Brute Force Intake
- Mopar Performance ECU

- 275hp-395ft/lbs at the crank (est.) Track results in the spring!!!
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post #12 of 13 (permalink) Old 01-07-2008, 11:35 AM
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sounds like typical 10% ethanal mix to me. try to find somewhere with regular gas.
No going to find it on the East Coast. Sucks.

Bob
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post #13 of 13 (permalink) Old 01-07-2008, 05:37 PM
Who is John Galt?

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No going to find it on the East Coast. Sucks.

Bob
Same in the Midwest

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