My glow plug light just quit working. I tested the relay, its good, then the plugs for continuity, and the number 1 plug is no good. The rest check out and have 12v when glowing. BUT, when I try to start after a complete (30 sec..until the relay clicks off) glow cycle, it just cranks. Takes a long time to fire. When all 5 plugs were working, it would glow for 10-20 secs and start without very much trouble. Wouldn't fire right off, but it would start on the first attempt.

So my question is, will 1 bad glow plug really make that much difference? Is it that hard to start when 4 plugs are good?

Thanks,
-Geoff

EDIT
2nd question: I'm about to order glow plugs. Should I replace all of them at once or just the bad one (what's commonly done)?

__________________
1985 300TD-euro 352,000 mi
1974 240D (1?)52,000 mi - has a new home now