Like the title says, does a VAFC help to improve fuel economy if you lean out the fuel curve?

 

It can, if you do it right using a wideband 02. The VAFC has some limitations as to how you can lean things out (like you can't adjust fuel ratios for various levels of MAP, except for WOT, or 50% and above as the VAFC considers it).

Just make sure you use a wideband to do it and you can lean out your cruising AFR to get better mileage. If you try and guess you can lean things out too much, making your ECU compensate by pumping in more fuel, or cause damage.

 

How much more fuel economy can you possibly need?

I miss my H22a, my WRX sucks down gas, stock 440cc injectors will do that I guess.

 

Dude I get like 19mpg (all city driving), it sucks. But I guess it's better than a Ram or F150

 

VAFC can be tuned to any settings that you want.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by integra15 &raquo;</TD></TR><TR><TD CLASS="quote">Dude I get like 19mpg (all city driving), it sucks. But I guess it's better than a Ram or F150</TD></TR></TABLE>

thats pretty damn low, r u sure something isnt wrong?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Dougs96SI &raquo;</TD></TR><TR><TD CLASS="quote">VAFC can be tuned to any settings that you want. </TD></TR></TABLE>

NO
vafc will only let you tune WOT/closed loop fuel settings. For daily driving, LTFT tunes out whatever settings you throw in for partial throttle, the map will correct itself. All efforts to tune partial throttle are futile... dont waste your time.... its been tried before.

but yes, you technically WILL save gas, but nothing significant unless you're serioulsy driving WOT every time you get behind the wheel. If you want better gas mileage, change your wires, plugs, cap, rotor and O2 sensors.

 

Thanks for the info, I think I will just try to lay off the gas a little.

 

That's not that bad where I come from.....
My minivan gets 13mpg on a decent day....11mpg on a cold day and that's driving normal.
My Prelude gets good MPG though, like 20-23....or 25mpg on the highway...That's good for where I live where we have huge hills and very very cold days which cause fuel economy to go Way down.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by lenn &raquo;</TD></TR><TR><TD CLASS="quote">

NO
vafc will only let you tune WOT/closed loop fuel settings. For daily driving, LTFT tunes out whatever settings you throw in for partial throttle, the map will correct itself. All efforts to tune partial throttle are futile... dont waste your time.... its been tried before.</TD></TR></TABLE>
Does this only apply to OBD2 ECU's?

Because why would the VAFC come with low throttle correction and high throttle correction?

 

Bump

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by lenn &raquo;</TD></TR><TR><TD CLASS="quote">
NO
vafc will only let you tune WOT/closed loop fuel settings. For daily driving, LTFT tunes out whatever settings you throw in for partial throttle, the map will correct itself. All efforts to tune partial throttle are futile... dont waste your time.... its been tried before.
</TD></TR></TABLE>

I think MAP signal is one variable that continously used regardless if the ECU is in open or closed loop.

With the car idling, you can lean out a VAFC until the engine quits.

 

yeah buy 2 new o2 sensors at over 150 a pop... screw that!!! why would you replace an 02 that works fine... Check yor 02s if they need to be replaced then do it if not then save yourself 300 bucks for gas money.

I agree on the tune-up... Check ur air filter and check ur plugs. If your plugs look black your rich...if they look light grey your lean. easy check to see wats goin on.

 

Ya know, I've been doing this on my 87 Teg and I think what lenn said is right.

Got the idea from here:

http://www.g1teg.org/phpbb/vie...ight=

Most of the time your ECU is adjusting the fuel based on what the O2 sensor is telling it (closed loop), it is trying to keep the A/F ration closest to 14.7 as it can. Most of the time I'm cruising around at 14.2 or 14.3 to 1. Under WOT the ECU relys on the MAP charts to determine fuel injector duration (open loop), this is when your SAFC comes in to play.

I was considering unhooking my O2 sensor to force the ECU to stay in open loop all the time, so my SAFC can be used to its maximum advantage. Also consider, my car is not OBD-1 or 2 like your Preludes, mine is OBD-0 with vacuum advance. My SAFC does not alter timing because of this.

Any thoughts?

 

If your car is ODB1 then the SAFC can be used for both open loop and closed loop settings. If your car is OBD2, then you can only tune for WOT. It's that simple...