He's saying that on diesels the alternator can be used as a source for the tachometer, which is true, via inductive pickup. Autometer and some other brands sell gauges/tachometers where it has a small pickup that straps to the alternator to measure the rpms. I am thinking of getting one of these. The instructions say to hook it all up, then calibrate it at a mph/engine speed you know to be accurate. It has all the instructions for this. I thought it was pretty cool. I'd probably just calibrate mine at idle to around 700-750, then I don't have to factor in torque converter slip....

The gauge is $114 though, so I am looking to mess with my OEM one some more before I abandon it and get the alternative.

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-diesel is not just a fuel, its a way of life-
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'17 Metris(VITO!) - 37k - wifes (OC-41k)
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'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)