Quote:
Originally Posted by lasitter
Diesels are great for producing gobs of torque at low RPM. I was going to say they don't have a throttle body either, but just now I'm reading that this has been added (when? what engines?) for the benefit of EGR systems. Sounds like a disaster to me.
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I'm not sure about other makes & models, but Cummins added the intake throttle to the Dodge engine in 2007 (with the change from the 5.9 to the 6.7). It's there for 3 reasons:
1)
EGR At certain relatively low loads there is a relatively small pressure drop between the exhaust & intake manifolds, so little or no EGR could flow without the throttle, even if the EGR valve was fully open. The throttle is closed down to lower the intake pressure to allow for more EGR flow. And, yes, it's a disaster for FE (but helps the emissions).
2)
"Thermal Management" Because of emissions it is sometimes required to make/keep the aftertreatment temperatures high. Most noteably, when the DPF needs cleaned out. The throttle can be closed down to raise the exhaust temps in order to burn off the carbon. And, yes, it's a disaster for FE (but helps the emissions).
3)
The shutdown "shake" In some cases, a diesel with a relatively high compression ratio with shutdown with a "shake" or "sneeze". Sometimes is stops so suddenly that the serpentine belt chirps. It's not really a problem, but some drivers don't like it. It's basically an effect of the compressed air in the motoring cylinders stoping the engine in its tracks. If the throttle is closed just prior to the engine shuting off less air gets into the cylinders and it comes to a more smooth stop.