South

I use to get around 425 km (264 mi) on a tank of gas. Now that there’s a mild cam and headers installed I’m seeing about 280 km (174 mi).

Does that sound right?

Jason

TXws6

iTrader: (10)

is it tuned yet?

1WICKDZ

iTrader: (2)

Depends on if your driving habits changed and if your city/highway ratio changed but I could see the difference being there. Might want to make sure the tuning is on too. Could be hurting you.

Also might help if it's an A4 or M6 into reasoning.

South

The car has been tuned. I drive a mix of city and highway, but it’s mainly highway driving. The car is an M6.

My driving habits haven’t changed. I understand this should result in worse gas mileage, since more gas is consumed now when I floor it, but I wasn’t expecting this big of a difference.

Thanks!

Jason

BIG_MIKE2005

iTrader: (116)

It shouldn't be that big a difference. I know a couple local guys who get about 300 miles to a tank with H/C packages. It's gonna be in the tune or you got a vacumm leak somewhere causing your fuel trim to spike out.

I was getting about the same milage as you when I had a vacumm leak. Wasn't throwin a code, but was WAY rich & the fuel trim was maxed out to compensate.

Patrick G

iTrader: (14)

Pure city driving for me is around 12 mpg, pure highway is 26+. That stop and go driving and short trips really brings down my mpg. 6th gear is where you get the great mpg.

My90Iroc

iTrader: (26)

I'll get low to mid twenties on the highway with my setup. Like patrick said, around town driving kills mpg.

When you're saying you get x miles out of a tank, how much are you actually filling up?

Are you running in closed loop or open loop?

I run open loop so the O2 sensors don't do anything. If you're in closed loop it is possible your O2 sensors are being fooled by the cam and adding fuel via the fuel trims.

Are you still using a MAF system?

purdueranger

iTrader: (11)

open loop here and get 12 in the city and 25 on the highway with 4.30 gears. this past holiday I got 20mpg in stop and go state road driving with the T-tops off. all depends on the foot. usually i only rev up to 2-2.5k when city driving since I have such a high numerical gear out back.

South

About 60L.

I've now had the car retuned and it's still doing the same thing.

hammertime

iTrader: (1)

Did you get a good drivability tune, or just the run of the mill dyno tune? If your tuner isn't logging data from some highway runs, trimming the fuel curve and looking at the spark curve, you probably won't see much difference. Have you changed gears? What heads/cam are you running?

Also, my stock '02 SS gets about the same miles on a tank of mostly city, some 'spirited' driving as your 'mostly highway' claim above. Maybe your either a little optomistic about how much highway driving you do, or your driving style is partially at fault.

Medic/Z28

iTrader: (9)

Silly question but whats the formula again? mileage / fuel in tank after a complete fill.

South

I'm still just commuting back and forth to work (~23 km) without any change in my driving style (which isn't too agressive) and I have lost 90 miles to the tank after the mods.

The tuner dyno tuned and street tuned. the car I don’t have the cam specs with me but I requested a cam and tune that would result in something that was very drivable daily driver. I have been told the cam is mild. I have no heads.

I’m not certain, but I think the tuner is having difficulties resolving an issue that I suspect is a contributing factor to the poor gas mileage. The tuner has had the car in his hands a couple times to resolve a “cruising” issue.

Basically, if I am driving around there appears to always be a load applied by the engine. If I pop the car into neutral, while driving (and do not keep my foot on the clutch), you can see the RPM gauge reads about 2600 RPM until you stop or push the clutch in.

If you push the clutch in and hold it there, while driving, the RPM slowly drops form about 2600 RPM to 900.

I’m not sure why, but I’ve been told my “sticky gas pedal” might also be related to the “cruising” -- When you first touch the gas pedal it requires more force to get it to move then it should. When you only want a touch of gas, you tend to overshoot.

Any more suggestions on what I should tell my tuner to look for?

Thanks,

Jason

South

MPG = [miles you got on the last tank of gas] / [the number of gallons it took to fill the tank]

hammertime

iTrader: (1)

Jason, the issue you describe could very well relate to fuel economy. If your car is slow to return to idle, you may almost never get into DFCO - Deceleration Fuel Cut Off. That alone can add up to a few miles per gallon.

I'm assuming you're in Canada somewhere since you've used metric units. Perhaps the colder climate is also part of your fuel economy issue. If your cam is that mild, the tune shouldn't be too much of a bear, or off a whole lot from stock. There are guys who wait a while getting 224 sized cams tuned, so maybe you could see how it does with a flash back to stock tuning.

slt200mph

iTrader: (42)

With mixed driving back and forth to work which is some city and some 2 lane highway I get 20.5 mpg..while on the highway I get 26.5 with a H/C & all the bolt ons car (MN6 w/3.42s) ... I ran 4.10s for about 40,000 miles and went from 310 miles per tank to 240 miles per tank with the 4.10s ..then went to 3.73s and picked up about 25 miles a tank..now with gas higher than giraffe ***** I'm back to the good ol 3.42s .. when the car was stock it got 29 on the highway..so the mods did not really drasticly affect my fuel consumption .. it was mostly the gear ratio changes that hurt the MPG .. but the fun mileage factor of the car increased a bunch with the taller gears ...