[T3] Fuel pressure and elevation

[Keith Park]

fuel pressure doesnt change with altitude, but gas mileage does, it goes up
with altitude.  if your fuel pressure is changing you have a bad regulator
most likely, or a plugged filter.

Keith


Topnotch Restorations
topnotch at nycap.rr.com
http://www.a383ina68.addr.com/radiorest/main.htm
71 Squareback  "Hothe"
65 Notchback  "El Baja Rojo"
93 RX7  "Redstur"
87 Golf  "Winterat"
 
-----Original Message-----
From: type3-vwtype3.org [mailto:type3-vwtype3.org-bounces at lists.vwtype3.org]
On Behalf Of Daniel Nohejl
Sent: Monday, August 22, 2016 9:51 PM
To: type3 at vwtype3.org
Subject: [T3] Fuel pressure and elevation

So a little over a month ago, we were in Yellowstone NP and had to diagnose
a running problem. In the process, we checked the fuel pressure and
discovered that it was only 25psi even though we'd set it to 29psi a few
months prior. Clearly elevation has an effect on fuel pressure. We live more
or less at sea level, but in Yellowstone we were anywhere from 6000'-9000'
above sea level.  

When we stopped by Jim's house on the way home a few weeks ago, he suggested
that we check the pressure when we got home. Of course we forgot until I did
some math the other day and realized we were only getting 22-23mpg on the
highway!! After checking, it turned out our fuel pressure was all the way up
to 33psi. 

Where am I going with this...? To ask a few questions:

-did VW dealers at higher altitudes re-calibrate the fuel pressure of FI
cars from factory before selling?

-if one is driving an FI car cross country and up and down significant
changes in altitude, is it worth re-calibrating fuel pressure if at high
altitudes for sustained periods?

-what (if any) would be the consequences of the fuel pressure being too low
when at a high elevation?

-I recall reading somewhere that Russ Wolfe regularly got 30mpg on his 68/69
cars and that one of his tricks to doing so was bumping up the fuel pressure
above stock. Clearly he didn't just do that or our MPG upon returning to
"regular" altitudes with high fuel pressure wouldn't have yielded bad gas
mileage. Can anyone verify that he was able to get such good MPG and does
anyone recall his methods?



Daniel
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