Weight reduction: not filling the gas tank

[ZugyNA]

Far as I know:

* gas caps have both a valve to let air IN (prevents tank collapse) and a high pressure relief valve (prevents a blown tank)

* evap systems work by taking any excess gas vapor (or liquid)......say after you've refilled on a hot day

* pressure builds up in the tank to the point it overcomes the valve at the canister...allowing vapor/liquid to go into the canister

* at times the ECU bleeds outside air in thru the bottom of the canister and this pulls the vapors from the carbon into the engine

In theory this is how an FA2000 should work...where you are providing a small amount of vapor using the PCV flow...haven't seen any gain yet with mine though.

[MetroMPG]

Sorry, clencherman - you lost me: what were you scrutinizing? Did you do a weight reduction test with the car?

Regardless, props for the "beware of one-tank conclusions" disclaimer.

[SVOboy]

He's saying the he only ran the first have of his tank to test the theory that a more full tank will get better mileage.

[MetroMPG]

Ah, gotcha. Thanks.

[Matt Timion]

Originally Posted by theclencher

Has someone with a scangauge or other reliable method checked for FE improvements at full tank-3/4 tank vs. 3/4 tank-empty? I just don't see it happening.

In my opinion weight reduction is one of those "last step" things, unless you are able to remove a few hundred pounds. I've mentioned this before, but my best tank was with a car full of people and luggage. Weight made little difference on that trip.

[MetroMPG]

Originally Posted by Matt Timion

I've mentioned this before, but my best tank was with a car full of people and luggage. Weight made little difference on that trip.

True, but that was in the days before CODFISHing, I'd wager. You can put that tank to shame with the stuff you've learned since then. And that happens to be the kind of driving that best benefits from reduced weight.

[ZugyNA]

I tried the same 1/4 tank refill with the 4 cyl and found the opposite....less mpg...then found that the ECU controlled valve that bleeds the canister didn't work...had a good spare and put it in. Didn't retest to see if it made a diff.

Any gas getting to the canister was wasted.

[Ted Hart]

Originally Posted by JanGeo

I remember when the Geo got down to 1/4 tank or lower it really takes off at a stop light and pegs you back in the seat compared to it with more fuel in the tank. Guess the fuel is a higher percentage of the weight in it.

Let me get this right: You run the "stoplight Gran Prix" in a Geo? Why??? -Ted