41
Figure 35
: Location of EGR value on Delica (circled). If the
valve has to be blanked off, do so by inserting a plate at the
arrow point.
10
EGR Valve
The exhaust gas re-circulation (EGR) valve is an active component in reducing
engine emissions, but if it fails then it can cause poor engine performance.
Consequently, some people desire to disable the valve. This section discusses the
facts about this and shows why this may not be the best solution.
10.1 Purpose
The exhaust gas re-
circulation (EGR) valve is
primarily there to protect
our environment. It does
this by introducing inert
burnt gas (from the
exhaust) to dilute the
oxygen concentration
thereby lowering the
combustion temperature,
thereby reducing the
formation of nitrous oxides
(NOx) and thus reducing
smog.
10.2 How the EGR valve works
[1]
The Engine control unit (ECU) detects accelerator position, Engine speed
and other transmission info, decides whether EGR is needed, and sends a
signal to the EGR. It should not activate EGR at idling, low load, or full load.
[2]
The pulsed electrical signal activates a solenoid, which opens a vacuum line.
In the 4M40 engine there are two solenoids. One controls whether the system
is on-off, and the other controls the degree to which it is on (duty).
[3]
Vacuum has separately been generated by a pump attached to the alternator.
(A diesel engine does not have vacuum at inlet manifold as does a petrol
engine.) The same vacuum is used for brake booster too.
[4]
The spindle in the second EGR valve moves when the vacuum is applied.
This permits a small amount of inert exhaust gas to be introduced to the