Hello everyone,
Recently the tachometer on my 1987 300D Turbo (124 Chassis, 603 series engine, 175k mi) has been showing a bit off in the high revvs range. Previously my redline when floored in neutral (as per shop manual) was
5200rpm, normal, now it's showing 4800rpm. Engine sounds the same, but it could be 400rpm lower and I don't notice.
Holding it in 2nd gear shows proper speed at maximum revs, but the tach still shows 4600-4700rpm. 80mph shows about 3000rpm in 4th gear, which seems normal.
The only changes recently have been fuel/oil filters (Wix brand from Napa auto parts, not proper OE brand) and top off of fluids (oil, coolant). Could the new fuel filter be the culprit, not allowing enough fuel into the engine for max RPMs?
Any help appreciated, Mike