You're quite right, the data blocks are very poorly named on the A8. I have loads of blocks saying duty cycle for instance but no clue as to what they actually are. After playing fr a while on the drive I plugged in the A4 to check a parking sensor issue and all the blocks are properly named. So having guessed on the A8 that 022 (rpm, pressure,pressure, duty cycle) was the one I was looking for, I got it up on the A4 and the same measuring block was rpm, fuel high pressure specified, fuel high pressure actual and inlet valve duty cycle. So I ran the 8 until it was hot, logging the whole thing. did a few starts, revved it etc.
Interestingly, all the cold starts had the duty cycle at around 10%. Pressure was more difficult as the actual start is obviously quick but here are a few snapshots...
10.22 0 351.9 0 10.5
10.85 105 351.9 27.6 44.1
11.46 147 282.9 82.8 34.4
12.08 147 282.9 96.6 33.6
12.71 735 365.7 496.8 22.3
column 1 is time stamp, 2 is rpm, 3 press specified, 3 press actual and 4 duty cycle. Thats data for one of the cold starts. They are all pretty much similar.
The next bit of data though is where it gets interesting and to be honest i dont really know what it means. I have put the data into a graph as its a lot easier to read. The first half of the graph is the engine idling, its been running for a while and is nice and hot. Specified pressure and actual pressure are equal, they dont really diverge much at all even when you red line the engine (I cut those bits out as it made the scale unreadable on the graph).
The second bit of the graph is shutdown and restart from hot...
The pressure drops immediately to zero on shutdown. The duty cycle goes up to 40 odds, specified pressure is 300 bar or thereabouts while actual pressure is hovering around the 80 bar area while its actually cranking.
Should there be a check valve on the HP pump? I woud have suspected that the pressure should be retained in the fuel rail and should actually rise with the heat soak on shut down.
I still need to find the sychronised yes/no measuring block. I will plug it into the A4 again and see if I can find it on there and go back to the 8 and see if its in the same place.
gill
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