cat /proc/engine
25. Jun 2008 
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Every engine in every car sold new today is controlled digitally so wtf is not having an abundance of cheap ODB2 cables and open source software that supports every damn car out there. Get with it, Internet.
So I picked up a VAG-COM the other week and have been slowly getting accustomed to being able to cat /proc on my car.
I can pull up so much stuff about my car. I started with seeing if the air flow being detected by my MAF sensor was about right and then went on to see if my turbo was working right through manifold pressure measurements. (I think the turbo is used somewhat like a throttle plate in a gasoline car, to regulate the air volume that is delivered to the cylinders. i.e. for load regulation, which is pretty cool and one of the reasons why diesel engines get my inner geek all hot and bothered.) They all tested fine so I’m now using it merely for amusement (or perhaps not), to compare fuel usage to and from work.
Seen above: two 25 km trips, north at highway speeds (on the highway, which is more or less indicated on the histogram) and south through traffic at 60-70 kph (see the big contribution of engine speeds < 1000 in the histogram). Weird that the highway trip used more fuel in total but it is a net up hill drive so maybe not so weird.
One thing that pisses me off about the tool is how it only lets you select predetermined sets of measurements. I.e. measuring block 16 gives engine speed, injected quantity, fuel use and some other stupid measurement when it would actually be more useful to have vehicle speed in there. You can have two “measuring blocks” logging at once but it slows down the poll rate, which already sucks at like 2-3 Hz.