87 300D Turbo -- Tach Malfunction?

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
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Anyone at all got any ideas? I'm still stumped!
ANY advice appreciated.
Mike

the
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check the clear filter but i would also clean off the contacts on the tach plug.
also i would guess every thing is fine if the driveability is the same as its been
case 240D 82 300SD 84 300SD 82 WAITING FOR MY SDL
the case, minus a few cans!
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Will do. Do you know where the tach plug is located? I've heard bell housing but that's it...
Could the inline filter be causing that much of a problem?
I'll advise when I look at the afforementioned... Thanks a bunch!
Mike

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Re: 87 300D Turbo -- Tach Malfunction? Group: alt.auto.mercedes Date: Thu, Oct 23, 2003, 5:06am (EDT-3) From: snipped-for-privacy@cox.net.remove (Mike"Rotor"Nowak) Will do. Do you know where the tach plug is located? I've heard bell housing but that's it... Could the inline filter be causing that much of a problem? I'll advise when I look at the afforementioned... Thanks a bunch! Mike
message check the clear filter but i would also clean off the contacts on the tach plug. also i would guess every thing is fine if the driveability is the same as its been case 240D 82 300SD 84 300SD 82 WAITING FOR MY SDL the case, minus a few cans! xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx the filter would make it a bitch to start
the case, minus a few cans!
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