Page 267 - Mechanic Diesel - TT

MECHANIC DIESEL - CITS

Liner EGR valves may also be equipped with an EGR valve position sensor (EVP) to keep the computer informed
about

• What the egr valve is doing
The EVP sensor also helps with self – diagnostics because the computer looks for an indication of movement
from the sensor when the it commands the EGR valve to open or close. The sensor works like a throttle position
Sensor and charges resistance. The voltage signal typically Varies from 0.3 (closed) to 5 volts (open).
• EGR system in diesel engines: The EGR systems are quite the same as those used in gasoline engines,
which means a sample of Exhaust introduced into combustion chambers to reduce combustion temperatures.
One of the main different is that most manufactures cool the incoming EGR gases before introducing them into
the cylinders. This reduces the temperature of combustion and therefore reduces the amount of NOx emitted
by the exhaust as shown in Fig.
Most systems with EGR coolers use engine coolant that passes through a separate circuit to cool the
recirculated exhaust Gases. The ECU/PCM operates and monitors the EGR system, EGR flow is controlled
by the ECU/PCM through a digital EGR valve. EGR flow will occur only when the engine is at a predetermined
level and conditions.

• Air injection system in to exhaust manifold
An air injection system which is also called SECONDARY AIR INJECTION in this system in exhaust manifold
injects fresh air into the exhaust stream to help burn any remaining fuel vapor, reducing harmful emissions like
carbon monoxide and hydrocarbons. It’s a component of the vehicle’s emissions control system.
In this system the vane type AIR pump drown air from filter and injection in exhaust manifold which helps to burn
unburn gases.

254

CITS : Automotive - Mechanic Diesel - Lesson 80 - 83