My 99 F350 diesel will not fire when the temp is below 40 degrees. Warmer than that and it fires right up.

Is there a sensor that may not be working that would richen the mix for cold temperature starting?

Also, I thought most (all) diesel trucks came with an engine heater. Can't find the plug on this one? Any thoughts? Could it be optional?

Thanks.

 

I'm assuming you don't have any codes or check engine light..
So I have to ask, are you getting a glow plug light on your cold start?
Are you allowing your glow plugs to fully cycle to do their job before you start your truck.

 

Correct... No codes or CEL. Wait to start glow plug light seems to be functioning properly. I'm thinking it may be a coolant temp sensor that has failed, and the EMC may think the engine is warmer than it really is ???

I'll change out the sensor and see if that helps.

Thanks.