They probably shouldn't be....
Mechanical injection engines mostly have some kind of "cold start " advance system that alters FIP timing until the engine warms up but this is pretty crude so leads to mechanical engines being often a bit noisy till they warm up. They are limited in how they can respond to demands .
Common rail engines can via the ECU pretty much infinitely vary injection timing and duration and rail pressure so typically run the same hot or cold...... unless they have a sensor that's gone duff and is feeding incorrect inputs to the ECU.... within the parameters set the engine ECU will try and meet whatever it "sees" is demanded and the state the engine is in regards temperature , load , and speed .