Accuracy of Gas station pump

[theholycow]

I got this one for $20, although it's $25 now:
http://www.harborfreight.com/fuel-in...ter-92699.html
It worked for my 2002 GMC, but I don't know if it fits whatever's in the VX.
"Fits most systems (except for Bosch, CIS-Jetronic and GM throttle body systems)"

[pgfpro]

I too think you might have a fuel pressure difference via fuel regulator or wiring or fuel pump voltage change?

On all my Hondas and DSM's its one of the first mods I do is re-wire the fuel pump with a bigger gauge wire.

[benfrogg]

So, I'm still all about the fuel pressure side of things, but here's some news.

I pumped one gallon into a gas can. I brought it home and measured it with a 2 cup measuring cup. There are 128 ounces in a gallon. That's 16 cups.

Perplexingly, I got 17 cups of fuel.
Now, I pumped very slowly (not at all on the fill up setting). I also got less than the normal fill up. (only one gallon)
This tells me I'm on to something....
Pumping slowly may change things. Look at this article:
http://www.npr.org/templates/story/s...toryId=5304258

NORRIS: One of the things that I thought was surprising when I read this story in the Seattle Post-Intelligencer was this suggestion that the speed at which you pump the gas can actually affect the accuracy of the meter's reading. What's the story there? What explains that?

Mr. DOUGLAS: I'm not a technician so I can't tell you technically what's going on, but what happens is, and this is what the typical customer does, I know it's what I do, you go in and you hold the handle on the nozzle all the way down so it fills up as fast as you can, or you set it with the little lever on the handle to the fastest speed that it will go. And we find statistically if you do that, the pump is going to deliver slightly less fuel then if you were to set it at the slowest notch that you can set it on the handle. But again it's an amount that is not terribly significant to the customer.

I found this:
http://www.bimmerfest.com/forums/sho...d.php?t=139828

And a few other articles skimming the net on the topic.
http://www.fredericksburg.com/News/F...5312001/296679

The stations typically dispense 1, 5, and 10 gallon increments correctly and other increments incorrectly. 1,5, and 10 are the normal testing pump numbers. So, those amounts are usually right on (within 5% accuracy).

I've been using the same pump for the duration of my gaslog, with only a couple of exceptions. A couple of exceptions that have been higher MPG too.

It seems there some weight to my argument about incorrect pumps.
B

[benfrogg]

Okay, so more reading has proven more results.
It seems that in Maine, testing is done with 5 gallon containers. All pumps are tested this way. That means, I'm very likely to get 5 gallons if I pump only 5 gallons. So, if I watch the MPGUINO till it says I've used 5 gallons (half a tankish) then go to another pump (or the pump in question) and my MPG's go up when I top off the tank, I know there's a scam going on.
My first boss is the guy who goes around and checks the pumps for accuracy. I need to look him up!
B

[bowtieguy]

i do think pumping slowly makes a difference...http://www.gassavers.org/showthread....pumping+slowly

[JanGeo]

Wow that is amazing that you an entire cup extra by pumping slowly . . . Guess what I am doing the next time I fill up . . . Going for ten gallons and pumping slowly!

[benfrogg]

The weights and measures test is done at both the slowest stetting and the fastest. They must pass both. It seems filling slower does have some weight to it.
B

[benfrogg]

News-
Filled up last time at the new station. A sad 53mpg. But, I got a tank distance record on this fill up! That means that the old pump was not topping off nearly as much as the new gas station/pump. The new number was 64 mpg much closer to the MPGUINO. Let's see if it stays there! I'm psyched to see 64mpg on a 716 mile tank.
If a couple of tanks go by that are obviously better than the last station, a call to the sate is in order.
Turns out it pays to pay attention!
B