I'm stumped. 85 300SD with 225k. Morning start rough, smokey, stalls, nails. First 3 miles pretty tough. Will run 85 mph afterward. Idles fine. No smoke. Starts fine when warm. Come off highway ramp after 1 hr at 70+mph and won't accelerate. Even floored. Vacuum fine. No oil in the water no water in the oil. Replaced injectors. Seemed to make it worse (Bosch reman.) Replaced filters. 85F ambient at start. Nailing says air leak. Can't fine one. Tank strainer seems fine. Lift pump? Help.

Sounds like a glow plug issue and maybe a clogged ALDA line.

Air leaks can be tricky to find.

Do you have an updated primer pump?

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83 SD

84 CD

Sounds like the glow plugs, cold compression test, fuel pressure to the injection pump and perhaps the valve clearances need checking. Maybe air ingress as well. New fuel filters of course as well.

Valve clearances before any compression check of course. In other words a general tuneup as the engines needs with time may have been totally ignored.

Probably should include a fuel system cleaning as well. You know cleaning the tank filter or at least seeing if the hose at the back is still capable of good flow. Make sure the fuel tank vent is open as one of your symptoms may involve being obstructed causing after the highway run issues. You can try a run with the fuel cap pretty loose or off to verify this I suppose as well.

The nice thing about all this is in general it is cheap to do yourself and you will even possibly learn something from the exercise. I forgot as well injector pump timing and a check for excess chain stretch. Then if you have not caught the problems you can go looking at is the injection pump shutoff staying partially on when it should not be.

The archives can address the best way to tackle each and every component of a solid check up and tune up. This tends to keep the engine more reliable in service as well.