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I have an Audi 3.0 TDI that I've been running for awhile and just recently I've been having an issue with the engine speed all of a sudden showing +-75 rpm fluctuations in the space of less than 1/10 of a second. See where the yellow bar indicates the beginning of the problem). I doubt very much that this can physically happen and the engine runs rough enough either as cause or as effect that it loses rpm.
I have posted a screen shot of the engine speed channels. Any ideas? I can provide access to the logs if that would help.
Is this a bad crank position sensor, a bad injector or something else?
Please post the actual data as too hard to tell what is going on with just a screen grab as there are channels we want to see which are not in the image. Unfortunately your diagnostic channels are all in the same colour.
I think I have just discovered my problem. The bolt holding the crank position sensor was too long, installed long ago by someone else, and therefore it was tight and bottomed out but the sensor was able to move in and out by about 3 or 4mm. No doubt a bit of vibration on the engine would cause it to move thereby creating the erroneous engine speed readings that disrupted the rest of the tune that relies on engine speed. It's raining today so I can't take it out to test the fix till tomorrow. I'm fairly confident that this was the problem though.
Once I get it sorted I might post some run data to a dropbox account so you guys can take a look at my tune and possibly suggest improvements to optimize it.