"Can a poor ground cause the GPs to fail?"

The glow plugs are grounded pretty good to the head/ block. You mean from a bad ground strap? I would say no. That would result in less power to the glow plugs and they just won't get as hot as with a good ground.

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked