I'm trying to track down a strong smell of diesel in the truck. I smelt the heating vents and its not coming through there. I looked under the hood and could not see any leaks. Any suggestions on where I should look / check?

 

Check the fuel drain valve on the fuel filter. And the lines going to the fuel filter.

There ids also a line going down the RH head that leaks under a clamp.
One of the Professors will post up soon, and give you some some positive ideas.

 

As mentioned above,get a flashlight and crawl on top of the motor to where you can see the fuel bowl.Look down in the valley and if you see fuel clean it up.Make sure you are clear and start the motor.Look for leaks as it is running unless you find the leak on inspection.The fuel drain valve is known to leak after changing filters if the orings are shot or hard.

Welcome to guzzle's PSD Fuel Filter Drain Valve Repair Web Page

 

I second the motion, when the fuel drain valve leaks, you get a strong whiff of diesel if you were to turn the heater or AC on.

 

My oldest son just went thorugh this and once he replaced the drain valve o-rings, all is good and dry.

 

If your fuel valve is leaking the drain tube is very wet and is dribbling from the tube and down the fuel bowl and into the valley. This means that the fuel is eating up your o-rings a little. With this in mind it might be a good time to replace all of the o-rings in your fuel bowl, ie over haul your fuel bow. takes about 2-3hours going really slow. The o-rings are a wear item and those to the fuel rails should also be replaced. Give Bob a call.
Welcome to guzzle's Powerstroke Fuel Bowl Rebuild Web Page

 

All good points thanks, my main problem is it is intermittent and seams to only happen when I can't take a good hard look. I'll throw the flash light in the truck. I never thought about the drain tube I always focussed on the fuel bowl it self lol

 

Mine started leaking bad when the weather turned cold.

 

If you have never changed the o-rings in the fuel bowl drain,then it is way past time. By pass the Dealers as they will not sell you the o-rings, but the full valve 'set'. the fuel 'valve' is 'fine'. It is the o-rings that wear out. the cold/weather change may be causing the o-rings to 'harden' and then because 'looser' as the truck is driven. the leak will almost be unnoticeable, but there will be some fuel in the valley.

 

You don't need to run the engine to check for fuel leaks. You just need someone to recycle the key about every 20 seconds or whenever the fuel pump stops running. Much safer to climb up on top when the engine isn't running. Heck of a lot cooler too.