Well, bolstered by the success of my valve adjustment and tune up, I decided to help a friend do the same to his 84 300CD.

We adjusted the valves, changed both fuel filters (pre filled the spin on) and changed the air filter as well.

Car starts right up and idles smoothly, but on the road it is a different story. It accelerates normally and runs good up until about 45 or 50. If you try to accelerate at highway speeds, it will hesitate and stutter (if it was a gasser I would say it was missing) It will not go above 65 or so floored unless you are going downhill, and when it is floored you get a decent amount of black smoke.

Going uphill, it will damn near slow down to a crawl. We started up a 1/2 mile hill at 60, and even floored it stuttered like hell and barely crested the hill at 25! Then going downhill it acted fairly normal until you put it under load at highway speed or hit another hill.

Back home, I re-tightened all the fuel filter connections and the noted the plastic primary filter has only a small fuel bubble in it. Road tested it again, and no change.

As I said, it starts right up, idles fine, and drives well up to about 50 MPH or when you try to put it under load. Then no power at all (no turbo feel either)

Sorry for the long post, but I want to help him fix his rig. Do you think we screwed up the valves? New filters shouldn't cause this should they? A new air filter wouldn't either would it?

I'm thinking a fuel delivery issue But could a bad valve adjustment cause this?

Glenn

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2012 Mercedes ML350 Bluetec 102K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 238K (mine)
1998 Volvo S70 T5 Turbo 211K (kids)
1994 Ford F150 4WD 246K (firewood hauler)
1983 Mercedes 300D 384K (diesel commuter)