How are the plugs wired? How did you get 12 volts to them all? If the glow plugs are all working, 12 volts to them should get them hot. Is he using the original relay with 12 volts coming from the strip fuse holder on the firewall just behind the engine? The only other areas to check are compression, air and fuel.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13