Volkswagen Corrado (1993 year). Manual - part 130

 

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Volkswagen Corrado (1993 year). Manual - part 130

 

 

EMISSION CONTROL VISUAL INSPECTION PROCEDURES 

         Three-Way Catalyst + Oxidation Catalyst (TWC + OC)
         This system contains a TWC converter and an OC converter in a
common housing, separated by a small air space. See Fig. 6. The 2
catalysts are referred to as catalyst beds. Exhaust gases pass through
the TWC first. The TWC bed performs the same function as it would as a
separate device, reducing all 3 emissions. As exhaust gases leave the
bed, they pass through the air space and into the second (OC)
converter catalyst bed.
         Visually check for presence of catalytic converter(s). Check
for external damage such as severe dents, removed or damaged heat
shields, etc. Check for pellets or pieces of converter in the
tailpipe.

Fig. 6:  Typical Three-Way + Oxidation Catalytic Converter
Courtesy of General Motors Corp.

         FILL PIPE RESTRICTOR (FR)

         A fuel tank fill pipe restrictor is used to prohibit the
introduction of leaded fuel into the fuel tank. Unleaded gasoline pump
dispensers have a smaller diameter nozzle to fit fuel tank of vehicle
requiring the use of unleaded fuel (vehicles equipped with catalytic
converter).
         Visually inspect fill pipe restrictor(s) for tampering,
i.e., restrictor is oversize or the flapper is non-functional. If
vehicle is equipped with an auxiliary fuel tank, ensure auxiliary fuel
tank is also equipped with a fill pipe restrictor.

         EXHAUST GAS RECIRCULATION (EGR) SYSTEM

         Single Diaphragm EGR Valve
         This type uses a single diaphragm connected to the valve by a
shaft. Diaphragm is spring-loaded to keep valve closed in the absence

EMISSION CONTROL VISUAL INSPECTION PROCEDURES 

Fig. 7:  Typical Single Diaphragm EGR Valve
Courtesy of General Motors Corp.

         Dual Diaphragm EGR Valve
         This type uses 2 diaphragms with different effective areas
and 2 vacuum sources. Although similar to the single diaphragm type,
the second diaphragm is added below the upper diaphragm and is rigidly
attached to the valve seat. See Fig. 8. These diaphragms form a vacuum
chamber which is connected to manifold vacuum.
         During highway cruising when manifold vacuum is high in the
center chamber, manifold vacuum tends to pull the valve closed.
However, the vacuum signal applied to the top side of the upper
diaphragm overcomes the downward spring force and the manifold vacuum
pull, due to the diaphragm's larger piston. This regulates the amount
of EGR.
         When manifold vacuum is low during acceleration, the higher
vacuum signal opens the valve, permitting more EGR. When manifold
vacuum is high during highway cruising, the valve is only partially
opened, reducing the amount of EGR.
         Verify EGR valve is present and not modified or purposely
damaged. Ensure thermal vacuum switches, pressure transducers, speed
switches, etc., (if applicable) are not by-passed or modified. Ensure
vacuum hose(s) to EGR valve is not plugged.

EMISSION CONTROL VISUAL INSPECTION PROCEDURES 

         Positive Backpressure EGR (BP/EGR) Valve
         This type uses both engine vacuum and exhaust backpressure to
control the amount of EGR. It provides more recirculation during heavy
engine loads than the single diaphragm EGR valve.
         A small diaphragm-controlled valve inside EGR valve acts as
a pressure regulator. The control valve gets an exhaust backpressure
signal through the hollow valve shaft. This exhaust backpressure
exerts a force on bottom of control valve diaphragm. The diaphragm
plate contains 6 bleed holes to bleed air into the vacuum chamber when
backpressure valve is in open position. See Fig. 9.
         Verify EGR valve is present and not modified or purposely
damaged. Ensure thermal vacuum switches, pressure transducers, speed
switches, etc., (if applicable) are not by-passed or modified. Ensure
vacuum hose(s) to EGR valve is not plugged.

EMISSION CONTROL VISUAL INSPECTION PROCEDURES 

         Negative Backpressure EGR (BP/EGR) Valve
         This type has the same function as the positive BP/EGR valve
except valve is designed to open with a negative exhaust backpressure.
The control valve spring in the transducer is placed on the bottom
side of the diaphragm. See Fig. 10.
         When ported vacuum is applied to the main vacuum chamber,
partially opening the valve, the vacuum signal from the manifold side
(reduced by exhaust backpressure) is transmitted to the hollow stem of
the valve. See Fig. 10. This enables the signal to act on the
diaphragm, providing a specific flow. Thus, the EGR flow is a constant
percentage of engine airflow.
         Verify EGR valve is present and not modified or purposely
damaged. Ensure thermal vacuum switches, pressure transducers, speed
switches, etc., (if applicable) are not by-passed or modified. Ensure
vacuum hose(s) to EGR valve is not plugged.

 

 

 

 

 

 

 

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