I beleive that they go hand in hand. Initially it is adding fuel that allows for increased exhaust gases which allows the turbo to spool up. As the turbo spools and builds boost it is forcing more air into the engine and the engine needs more fuel to avoid going into a lean condition and causing combustion temperatures to get too high.
Hopefully if I am incorrect, one of the diesel experts on here will educate both of us.
All of our Diesels have boost referenced fueling; even us first genners had a spring-loaded cone that results in increased fueling under high boost conditions. Second genners have a similar mechanical AFC solution, while the later trucks have whatever computer-controlled solution.
Yes, they go hand in hand, but, a diesel is different with rich/lean and hot/cold EGT.
More fuel is higher EGT, less fuel is lower EGT.
More air is lower EGT, and less air is Higher EGT.
You can burn up a motor by putting alot of fuel and little air to it.
However, having 10psi boost at idle and the EGT's will be very cold, and the engine would last a long time as long as you don't wash down the cylinders with raw fuel.
If you were driving down the road, and were able to control your boost, maybe by using a Holset HX-40VGT hooked up to a manual cable so that you could change the exhaust housing on the fly, and had the housing pretty far open and only making 5 PSI at 70MPH, your EGT would be pretty high, and if you really cranked it open, and made the engine go "rich" you might even be able to "melt" a piston from Very High EGT from lack of air, however, if you were to close it back up to a "normal" 10PSI, your EGT's would come back down to a safe range.
Now, do the opposite, and cruise at 70MPH with 10PSI, and crank that exhaust housing real tight and make 25PSI boost and you will see your EGT drop down several hundred degrees.
More air is less EGT and to a point, safer, where, less air is more EGT and can only go so high before engine damage is incurred, either immediate, or long term.
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