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Was wondering why my 99 Cummins is SO much louder than my buddy's 07? Is it better insulation inside the newer truck or is the engine actually quieter? Thanks

I can explain it a bit better... But the 03 and up Cummins engine use a pilot injection pulse to preload the cylinder with fuel before the main event. This pilot injection is what reduces the audible knock of the engine. But like some are finding out if you use a EFI Live tuner and disable the pilot injection pulse it knocks just like the old 2nd Gens but the MPG's will rise up even more. Seem like the older and less BS that was on the engine the better the MPG's were...
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Yes, as Moparman stated, its because of the injection pulses. The "clatter" that diesels make is because of the noise you hear from the diesel fuel combusting during the combustion stroke. Amazing that it would be that loud but it is. Because the 2nd gen trucks have mechanical injectors there's no way to change what each injector does without affecting all the injectors, but when the newer injection systems where introduced, they use electronic injectors which allow multiple shots of fuel in the cylinder during that same combustion stroke. So in short, one big spray of fuel equals a big bang but many small sprays of fuel equal many small bangs, which equals less noise. Thats not all they did to reduce engine noise but thats the biggest contributing factor.

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