I haven't looked at one, but even a diesel has to have some system to measure the volume of air entering the engine to determine the fuel charge to spurt into the combustion chamber. Mass Air is a good metering system because it is on the front side of the engine, so as long as the engine computer is good and you don't trick out, or "bomb", the engine out too much it will learn and adapt to modifications.
The way it works is,... or was on a Mustang 5. 0, the mass air body is a metal cylinder with computer module on top, located right behind the air filter (on the engine side of the air filter. ) Inside the metal cylinder, which is a good size 3 inches across, there is another metal tube along one of the edges of the cylinder. The tube is probably 1/4" across, stretched across the inside the tube there is a thin wire. This wire is heated and is connected to the computer module. The computer tests the temp. of the heated wire to determine how much air is entering the engine. As more air flows through the meter the wire gets cooler and vice versa. The computer then likely does all kinds of calculations about how cold and dense the outside air is and how much is entering the engine, and throttle position, load, blah, blah, blah, and figures out how much fuel to shoot.
As I said earlier, good thing about this set up is that as you put on a bigger exhaust, free flow air filter, tear of your cat (who would do such a thing!!), install better intake/heads, etc. (all of which improve engine efficiency and suck more air or allow the engine to breath better and need more air) the computer just adjusts the fuel ratio based on the increased amount of air entering the engine. This works to a point until the modifications outstrip the ability of the computer to adapt to the performance increases. (On Mustangs you were good until you really "bombed" it by putting on sizably larger injectors (30+lb. vs. stock 19lb. ) and a supercharger or turbo. You could increase HP by at least 50% via less exotic means before you need to fiddle with the computer or mass air. )
So, in summary, I don't know if the '03 CTD has a mass air meter, but if it does, I wouldn't necessarily consider that to be a bad thing. But then again... . my experience has been a completely different application.
If none of this helps, be gentle with me in your comments, I am sorry if I wasted your time with a FERD car story.
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