As I am still a new owner to the PSD 'S I would like to know how do you tell when glow plugs are starting to go bad. My truck is a 97 f350 crew with the 7.3 psd. I am still going thru the truck inch by inch cleaning up the previous owners small messes. Nothing major just little maintenence issues. On a cool summer day, after its sat for a week it will not start right after the glow plug lite goes off, some times I need to try it two more times before it starts. Once it's warm, it will start great every time. I'm a little woried that when we get to our cold winter if it will start. What are the signs of glow plugs going bad?

 

You may have 1 or 2 of them that are bad try testing them all to see if that is the problem if not your relay may not be working right or you may even have a compression problem.

From thedeiselshop.com

Glow Plug Test with Ammeter
Source:
Graham Slieker


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The best tool for glow plug testing is a standard +-30 Amp ammeter. Glow plugs can fail in one of 2 ways. Either short or open.
Testing glow plugs with an open a continuity meter or Ohmmeter will work, but not if the glow plug is shorted. A shorted glow plug will pass current but it won't get hot, at least at the tip. When a resistive heating element gets hot its resistance goes up and the current flow for any given voltage goes down. When you put the ammeter in series with a glow plug and activate the relay the current will spike to about 40 Amps and decay to about 15 Amps over a 3 to 5 second period. If it's shorted the current will just go to 40 Amps and stay there because since the current is not flowing through the element (shorted at base of plug) heat build up doesn't occur and current doesn't decay.

6 inches of AWG #12 wire and standard male/female automotive bullet connectors is all you need. Also always replace glow plugs as a complete set not individually. As glow plugs age heat output per given current flows change. Replacing individual units will lead to cold jug starts (rough with white smoke) and generally harder starts in cold weather.