VAF adjustment experiment

[Dave G]

In an effort to improve the gas mileage in my 1990 5 speed Festiva, I'm experimenting with adjusting the VAF meter. Preliminary results are encouraging! The car was getting about 36 mpg in mixed city/highway driving. About 10 days ago I turned the VAF spring adjustment wheel 4 clicks tighter and filled the gas tank. Just filled it again today and found I got 42 mpg. I just turned it 2 more clicks, and will report back in a week or so. Here's a picture of what I'm talking about:

[mattswabb]

Be sure not to go to lean. Maybe look into an additional O2 sensor to read the AF ratio to be safe.

[Dave G]

Be sure not to go to lean. Maybe look into an additional O2 sensor to read the AF ratio to be safe.

I thought I'd keep an eye on the spark plugs to see how they are burning.

[Hot_Wheels]

isnt the top of that epoxyied on? how did you get it apart?

[mattswabb]

just cut it off carefully. Cut around the edges and pry it off. Mine on the BPT comes on and off now.

[festivaWES]

silixcone actually..when i did the s/k code hybrid i set it at factory setting. I was thinking about leaning mine out 4 clicks also....my A/F gauge shows that I'm in the stoich area under mild and full throttle.

[Dave G]

Hum... Have done some running around today and the exhaust stinks when idling - kinda like any car before cat converters. Could making it too lean make the cat stop working? I'm going to put it back at 4 clicks tighter. I can live with 42 mpg

[festivaWES]

I wouldn't go more than 4 clicks max, some guys where having problems with more than 4 over at the protege boards.

[FestYboy]

if you go too lean, you'll have a lean misfire (even if you can't feel or hear it) and that unburnt fuel will cause perminant damage to your cat. watching your plugs isn't accurate enough of an indicator, get an A/F meter or use a DVOM to monitor your ratio.

[Pu241]

Re: VAF adjustment experiment

In an effort to improve the gas mileage in my 1990 5 speed Festiva, I'm experimenting with adjusting the VAF meter. Preliminary results are encouraging! The car was getting about 36 mpg in mixed city/highway driving. About 10 days ago I turned the VAF spring adjustment wheel 4 clicks tighter and filled the gas tank. Just filled it again today and found I got 42 mpg. I just turned it 2 more clicks, and will report back in a week or so.

Dave G,
I log my fuel too!
As well as all maintenance.
This is the kind of stuff I've been looking for.
Just wondering if the change in weather has influenced your 36 to 42 mpg increase.
As I noticed an increase in my MPG from 40-42 during the cold weather, to 44 and 45 during the last few weeks.
Just for comparison I drive a '93 5spd with 200K+ miles.

[pole120]

Can we get a little more info on how to adjust this? I'm really interested in what I'm seeing here.

~Josh

[Pu241]

I'm interested in a group of us doing this after the weather stabilizes and we start to get consistent MPG numbers per tank, for those who do not already have a history.
I have, between my car and my wife's car, about 360,000 miles of documented fuel consumption data to work from.
As I screwed-up the VAF sometime ago (never undo the screws holding the electrical connector to the VAF body :evil: , had to solder the connection back on the VAF) I have easy access to make this adjustment.
It's covered by duck tape, and has been for the last 3-4 years!
Anyone know what a A/F ratio monitor runs?
Think I have an article on making your own.
Believe it was for the weekend racer, so shouldn't cost too much and was about 8-10 years ago!
Just need to find it!

Pu241

[warlocke]

if i can get a spare maf ill do this

[GenevaDirt]

Part of the fuel mpg has to do with the winter gas versus regular too. Right now it depends on which station I go to and whether or not they have switched fuel yet.
I hope they all get switched soon. I normally get between 40 and 45 in my 91 5 speed, this winter I was getting about 35-38. I have been back up to 42 depending on where I get my fuel.

[Pu241]

Part of the fuel mpg has to do with the winter gas versus regular too. Right now it depends on which station I go to and whether or not they have switched fuel yet.
I hope they all get switched soon. I normally get between 40 and 45 in my 91 5 speed, this winter I was getting about 35-38. I have been back up to 42 depending on where I get my fuel.

I agree, but can't attribute it all to "winter" gas, as I used to, because I noticed my mileage increased last month when we had a warm spell and then fell back again when it turned cold again!
As an estimate I figure about 2 to 2.5 mpg loss due to "winter" gas and another 2-2.5 mpg due to cold weather.

Hey anyone in Canada.
Do you have "winter" gas and if not do you see a difference in mpg based on temperature alone?

Pu241