[T3] Fuel pressure and elevation

[Daniel Nohejl]

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