Mightychan
Member
New to me 2005 420Da with 6CTAs. Port tach would wander around a bit, starboard was pretty stable. Wot registered 2700 on the starboard (stable) tach. Posted about this in the 420 Da thread and was told that there was a 4-6-8 switch on the back of the tach that would corrode and cause this behavior, just move it around and all will be fine. Pulled the panel and did not see what I would consider a 4-6-8 switch. What I found was a rotary control with 3 positions marked 103T, 126T, and 159T. Having no idea what those meant, I rotated the control between settings a few times (no detents) and returned them to the middle position, where they had been to begin with. The good news: port tach is now stable. The bad news: they both now read 2500 at WOT. So, have I messed up the calibration of the tachs? I don't understand why they would not both read 200 RPM less. Suggetions? Many thanks....