Why is gas mileage sucking so bad?
10-25-2011, 07:39 PM
#1
5th Gear Member
Thread Starter
Join Date: Jan 2006
Location: Florida
Posts: 2,398
Why is gas mileage sucking so bad?
Just figured i'd check and see what kind of input you guys had. The car for the past six or so months has been having a drastic and rapid decrease in mileage. I used to get roughly 320 miles till empty of mixed city/highway. Now I am getting 200 miles till empty if lucky. I cleaned the air filter, mass airflow, throttle body, had Ford do a fuel service even. Changed fuel filter. Car only has 45,000 miles.
I did add my larger 28.4 tall tires in the rear that are nearly 12 inches wide. 295/45/18s. I can't see how they would make THAT much of a difference. Other then that I am drawing blanks. Spark plugs? CoPs? I dunno. Appreciate any suggestions, thanks.
I did add my larger 28.4 tall tires in the rear that are nearly 12 inches wide. 295/45/18s. I can't see how they would make THAT much of a difference. Other then that I am drawing blanks. Spark plugs? CoPs? I dunno. Appreciate any suggestions, thanks.
10-25-2011, 08:41 PM
#2
I can't see a 100mile difference in a wider tire contact patch. Difficult to believe that a CoP or any other issue would be causing it without a C.E.L. but stranger things have happened. My two suggestions
1) Have you really paid attention as to how much fuel you're putting in? Your gauge may read empty but if the sending unit is no good it may read empty but you're only putting 10 gallons to fill up instead of 14.
2) Ask the dealer how much it costs to run a power balance test and a relative compression test, and injector flow test, that may reveal something.
1) Have you really paid attention as to how much fuel you're putting in? Your gauge may read empty but if the sending unit is no good it may read empty but you're only putting 10 gallons to fill up instead of 14.
2) Ask the dealer how much it costs to run a power balance test and a relative compression test, and injector flow test, that may reveal something.
10-25-2011, 10:02 PM
#3
How much did your tire diameter increase? You slowed down your speedo, so it will register fewer miles in the same trip.
It's not likely that that alone would account for the difference, if you just corrected it mathmatically. It is possibile that the effective change in gear ratio has altered your driving habits to detrimental effect.
It's not likely that that alone would account for the difference, if you just corrected it mathmatically. It is possibile that the effective change in gear ratio has altered your driving habits to detrimental effect.
10-26-2011, 07:36 PM
#4
6th Gear Member
Those tires are about 1" larger than stock plus you've added some rotating mass. But even with the speedo being off (and throwing the on-boards calculations off) and the extra work the engine has to do per tire rev, it shouldn't be THAT much of an impact. But add low tire pressure, aggressive driving and more stap-and-go and I can see it.
10-26-2011, 10:20 PM
#6
Join Date: Aug 2010
Location: TN
Posts: 18
I know exactly what it is. I have the same tire profile 295/45/18 Hankooks and I'm actually getting better gas mileage (26mpg) then my previous rear tires (275/35/18) at 25mpg. rightly so to because if you think about it I am actually running 2100-2200k at 70MPH right now, where as before I was running at 2300-2400k rpms at 70MPH with the 35s
I have an SCT x3 and had to recalibrate my computer to 750 Revs (tire rotations per mile). try that out, I bet thats your problem unless you dont have an SCT then your just going to have to go out and buy one
I have an SCT x3 and had to recalibrate my computer to 750 Revs (tire rotations per mile). try that out, I bet thats your problem unless you dont have an SCT then your just going to have to go out and buy one
10-26-2011, 10:22 PM
#7
Join Date: Aug 2010
Location: TN
Posts: 18
SORRY COMPUTER DIED ON ME JUST DISREGARD THE TOP POST
I know exactly what it is. I have the same tire profile 295/45/18 Hankooks and I'm actually getting better gas mileage (26mpg) then my previous rear tires (275/35/18) at 25mpg. rightly so to because if you think about it I am actually running 2100-2200k at 70MPH right now, where as before I was running at 2300-2400k rpms at 70MPH with the 35s
I have an SCT x3 and had to recalibrate my computer to 750 Revs (tire rotations per mile) according to my GPS. try that out, I bet thats your problem unless you dont have an SCT then your just going to have to go out and buy one
I know exactly what it is. I have the same tire profile 295/45/18 Hankooks and I'm actually getting better gas mileage (26mpg) then my previous rear tires (275/35/18) at 25mpg. rightly so to because if you think about it I am actually running 2100-2200k at 70MPH right now, where as before I was running at 2300-2400k rpms at 70MPH with the 35s
I have an SCT x3 and had to recalibrate my computer to 750 Revs (tire rotations per mile) according to my GPS. try that out, I bet thats your problem unless you dont have an SCT then your just going to have to go out and buy one
Last edited by ace555; 10-26-2011 at 10:26 PM.
10-26-2011, 11:17 PM
#8
5th Gear Member
Thread Starter
Join Date: Jan 2006
Location: Florida
Posts: 2,398
I have reprogrammed my computer to coincide with the increased tire diameter. My car came stock with the 235/55/17, and now the 295/55/18s which is about a 1.8" increase in height and about a 2-3" increase in width. Almost spot on with the GPS (and we have plenty of speed checkers posted up around here)
I just cannot see how I am dropping in fuel that much. Even my onboard mileage reading is saying 13mpg. As far as the pumps... it is pumping in the correct amount. I'm not really doing any aggressive driving and the tire pressures are 35psi. I have 3.55 gears. I too, thought that I would actually get a slightly better gas mileage since the tire diameter is actually making it more like a 3.31 gear. They are however, a lot heavier so I know that's pretty far fetched.
The car has been acting a little funny as well, I'm going to change the fuel filter again, and oil again, and clean the airflow sensor again, see if that does anything.
I just cannot see how I am dropping in fuel that much. Even my onboard mileage reading is saying 13mpg. As far as the pumps... it is pumping in the correct amount. I'm not really doing any aggressive driving and the tire pressures are 35psi. I have 3.55 gears. I too, thought that I would actually get a slightly better gas mileage since the tire diameter is actually making it more like a 3.31 gear. They are however, a lot heavier so I know that's pretty far fetched.
The car has been acting a little funny as well, I'm going to change the fuel filter again, and oil again, and clean the airflow sensor again, see if that does anything.
10-27-2011, 07:15 AM
#9
3rd Gear Member
Join Date: Dec 2010
Location: Oldham County, Kentucky
Posts: 540
I can't see a 100mile difference in a wider tire contact patch. Difficult to believe that a CoP or any other issue would be causing it without a C.E.L. but stranger things have happened. My two suggestions
1) Have you really paid attention as to how much fuel you're putting in? Your gauge may read empty but if the sending unit is no good it may read empty but you're only putting 10 gallons to fill up instead of 14.
2) Ask the dealer how much it costs to run a power balance test and a relative compression test, and injector flow test, that may reveal something.
1) Have you really paid attention as to how much fuel you're putting in? Your gauge may read empty but if the sending unit is no good it may read empty but you're only putting 10 gallons to fill up instead of 14.
2) Ask the dealer how much it costs to run a power balance test and a relative compression test, and injector flow test, that may reveal something.
10-27-2011, 08:59 AM
#10
Join Date: Aug 2010
Location: TN
Posts: 18
just an idea, try reprogramming with the xcal and if that doesn't work try unplugging your battery for 20mins or so to "reboot" the computer. It really just sounds like some form of a computer calibration problem to me. Does it feel like you only going short distances on one tank? like b4 you changed the tires could you go a week with out filling up where as now your filling up every half week?
