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Diesel Tuning Fundamentals: Throttle Body

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Throttle Body


00:00 - As we've already discussed, the diesel engine doesn't specifically require a throttle body in order to modulate torque like a gasoline engine.
00:08 We will however usually find that a throttle body is still incorporated in modern common rail diesel engines, however they're there for very separate reasons.
00:17 The throttle body which will usually be a drive by wire design can be partially closed by the ECU under low load conditions to help with exhaust gas recirculation or EGR which is critical to emissions control.
00:30 We will detail the EGR system later in the course but for now all we need to know is that the EGR system works by partially closing the throttle plate to create a pressure differential.
00:41 It's this pressure differential that promotes flow of the exhaust gas through the EGR valve and into the cylinder.
00:47 Without the throttle body the EGR system would be largely ineffective.
00:52 The other main reason a throttle body may be fitted is to aid with the shutdown of the diesel engine when it's turned off.
00:59 Closing the throttle body when the engine is shut down cuts off the air supply to the engine which can result in faster and smoother shutdown of the engine with less noise vibration and harshness which is an expectation with a modern electronically controlled engine.
01:14 The last potential use of the throttle body is to shut down the enigne is control of the fuel delivery is lost.
01:20 This is rare however in high mileage diesel engines that have not been maintained, it's possible for the injectors to leak or in extreme circumstances where the injectors are badly worn, the ECU may not be able to shut off the fuel supply.
01:35 Of course in this situation it's impossible to shut down the engine if we don't have some means of restricting air flow into the engine.
01:43 The lack of requirement for a throttle body actually contributes to the diesel engine's impressive efficiency when compared to a gasoline engine.
01:51 In a gasoline engine where we need to close the throttle body under cruise conditions in order to reduce the engine torque, this produces a high level of vacuum in the inlet manifold and inlet ports of the engine.
02:04 This results in what is referred to as pumping losses which simply means that it's harder for the piston to move down the cylinder on the intake stroke because it's working against a vacuum.
02:15 Diesel engines in non EGR operation do not suffer from these same pumping losses.

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