Check valve and injection timing -- it should not jump injeciton timing, but if it was set and the bolts aren't tight there is no reason to assume it would not change.

However, this being a 603, are you using coolant with no obvious leaks? The head cracks easily on this engine, and they also blow head gaskets, and one place that goes is the compression ring on the rear cylinder.

Your symptoms are low compression, or very early (not late) injection timing.

If you have sucking/blowing noises on the rear, I'm betting on a head gasket -- usually you get oil leaking out under the chain tensioner and at the right rear corner, too.

I just replaced mine.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!