Doing something wrong?

[vielecustoms]

I know this is going to seem strange. I may be doing something wrong here but my car seems to get worse mpg when I am taking it easy, than when I am driving normal? I have been driving with constant speed, and trying to keep a cirtian mpg on the scangauge, avoiding hard acceleration, gliding down hills in neutral, changed my route to a flatter, shorter one. I have not been lugging the engine but I am not hammering on it either. my scangauge is off showing more mpg than the car actually got last time (usually it is showing less than actual),
but this last fill up I was driving normal and got really good mileage compared to when I was taking it easy and trying to get better mpgs. Part of the problem is I used a diffrent gas station, because it was on the way (mobil), vs the one that is close to my apartment(sunoco). but I am getting the best results from the sunoco so I will get my gas exclusively from there from now on.

any tips or pointers?

[MechEngVT]

Accelerating harder and short-shift to keep load up to 75-80% and achieve cruising speed in as short a time as possible is preferable to *****-footing up to speed. Accelerating yields poor economy; minimize the time spent in this mode. Accelerating at WOT in open-loop enrichment yields horrendous economy so stop short of this limit (usually 85% load in most EFI programs). Short-shifting helps keep load up and prevents high piston speeds that increase internal frictional losses in the engine. Usually 2000 rpm is good unless your engine has a very short (less than 3.25 inches or so) stroke, at which point going up in RPM is ok.

[MetroMPG]

What you do after accelerating is far more important, in the big picture, than how you accelerate. EG. if you're regularly forced to brake after high load acceleration, your fuel economy will end up in the toilet compared to feather-footing up to a stop.

vielecustoms: also be careful about drawing conclusions about what works and what doesn't based on driving conditions / routes that aren't identical. EG:

-- as the weather gets colder your mileage is dropping.

-- If the new route is significantly short enough, you'll get worse mileage simply because the car spends proportionately more distance coming up to full operating temperature (not just the engine - the whole drivetrain, including transmission, tires, bearings...)

-- You might have had a short fill on the bad tank (unless you're filling to the brim every time)

-- Sounds like you're still dialling in the ScanGauge accuracy. If you're
"driving to a target MPG" when it's optimistic, that'll obviously lower your actual numbers.

You're in the Adirondacks, I see. You should consider going out to one of the AMEC economy events in the spring. Even if you didn't compete, I bet there are people who would be happy to talk to you / demo / give you a clinic on technique if you're interested.

[vielecustoms]

the new route is shorter but only about 10 miles, it is still about 25 miles each way, vs about 35 the other route. the new route is mostly 55 mph fairly flat with a few rolling hills, and only about 1/4 mile of city driving. the old route has several steep hills, 55 mph and about 8 miles of city driving.

I am still calibrating the scangauge, so I have not been as dependent on the numbers from that.

I will use your suggestions and do some more reading.

[brucepick]

vielecustoms -
Are you saying you got better mpg on the old route?

I would guess you'd get better mpg on the new route: mostly steady 55mph with few starts/stops.

Actual mpg is what counts of course, so you can't go entirely by the ScanGauge, especially if you change the adjustment after you fill up.

[KJSatz]

Originally Posted by brucepick

(snip) Actual mpg is what counts of course, (snip)

Just by having a route about 30% shorter you're saving a lot of gas, even if you lose some mpg's. Obviously there's a turning point there, but it would take a fairly severe decline in mpg.