I have a 99 7.3 that doesn't want to start when the ambient temp is below 55 deg. In the 40s forget it unless I plug the truck in. When the engine does start it seems like it was flooded. I replaced the glowplug relay and checked resistance at the glowplug wire leads (in spec). Can the glowplugs be bad and still check out ok? If not any suggestions? The truck has 280k miles on it. Any Help would be appreciated.

 

Check to see if the GPR is working. A simple test light will tell you if its working or not.