Does you glow plug light come on for a short time after the engine starts? If so you have 1 or more failed glow plugs.Easy test,unplug the harness from the relay connect the clip of your test light to the + terminal of your battery,touch the probe end to the connectors in the harness plug one at a time.Good glow plugs will cause the light to light,bad ones will not light the test light.Look closely at the harness plug and you will see that the sockets are numbered so you will know which ones are good or bad.Probably burned out one or more from extended starting attempts while you had the fuel lines crossed. My $.02 Don

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97 E300D 157000 miles
87 300TD ?141k? miles