I have read of very worn IP's that would not restart when the IP is fully hot, pouring water all over the IP to cool it off and will get it to restart, confirms that it is indeed a worn IP. Another confirmation of a worn IP is run a thicker fuel such as veg. If it restarts with a hot IP on veg and not on diesel, it also confirms a worn IP.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked