Volkswagen Corrado (1993 year). Manual - part 132

EMISSION CONTROL VISUAL INSPECTION PROCEDURES 

         The O2 sensor is mounted in the exhaust system where it
monitors oxygen content of exhaust gases. Some vehicles may use 2 O2
sensors. The O2 sensor produces a voltage signal which is proportional
to exhaust gas oxygen concentration (0-3%) compared to outside oxygen
(20-21%). This voltage signal is low (about .1 volt) when a lean
mixture is present and high (1.0 volt) when a rich mixture is present.
         As ECM compensates for a lean or rich condition, this
voltage signal constantly fluctuates between high and low, crossing a
reference voltage supplied by the ECM on the O2 signal line. This is
referred to as cross counts. A problem in the O2 sensor circuit should
set a related trouble code.

         COMPUTERIZED ENGINE CONTROLS (CEC)

         The CEC system monitors and controls a variety of
engine/vehicle functions. The CEC system is primarily an emission
control system designed to maintain a 14.7:1 air/fuel ratio under most
operating conditions. When the ideal air/fuel ratio is maintained, the
catalytic converter can control oxides of nitrogen (NOx), hydrocarbon
(HC) and carbon monoxide (CO) emissions.
         The CEC system consists of the following sub-systems:
Electronic Control Module (ECM), input devices (sensors and switches)
and output signals.

         EARLY FUEL EVAPORATION (EFE)

         The EFE valve is actuated by either a vacuum actuator or a
bimetal spring (heat-riser type). The EFE valve is closed when engine
is cold. The closed valve restricts exhaust gas flow from the exhaust
manifold. This forces part of the exhaust gas to flow up through a
passage below the carburetor. As the exhaust gas quickly warms the
intake mixture, distribution is improved. This results in better cold
engine driveability, shorter choke periods and lower emissions.
         Ensure EFE valve in exhaust manifold is not frozen or rusted
in a fixed position. On vacuum-actuated EFE system, check EFE thermal
vacuum valve and check valve(s). Also check for proper vacuum hose
routing. See Fig. 15.

EMISSION CONTROL VISUAL INSPECTION PROCEDURES 

         EMISSION MAINTENANCE REMINDER LIGHT (EMR) (IF EQUIPPED)

         If equipped, the EMR light (some models may use a reminder
flag) reminds vehicle operator that an emission system maintenance is
required. This indicator is activated after a predetermined
time/mileage.
         When performing a smog check inspection, ensure EMR
indicator is not activated. On models using an EMR light, light should
glow when ignition switch is turned to ON position and should turn off
when engine is running.
         If an EMR flag is present or an EMR light stays on with
engine running, fail vehicle and service or replace applicable
emission-related components. To reset an EMR indicator, refer to
appropriate MAINTENANCE REMINDER LIGHTS in the MAINTENANCE section.

         MALFUNCTION INDICATOR LIGHT (MIL)

         The Malfunction Indicator Light (MIL) is used to alert
vehicle operator that the computerized engine control system has
detected a malfunction (when it stays on all the time with engine
running). On some models, the MIL may also be used to display trouble
codes.
         As a bulb and system check, malfunction indicator light will
glow when ignition switch is turned to ON position and engine is not
running. When engine is started, light should go out.

EMISSION CONTROL VISUAL INSPECTION PROCEDURES 

ENGINE OVERHAUL PROCEDURES - GENERAL INFORMATION 

         Engine Overhaul Procedures - General Information
         ALL PISTON ENGINES

         * PLEASE READ THIS FIRST *

         Examples used in this article are general in nature and do
not necessarily relate to a specific engine or system. Illustrations
and procedures have been chosen to guide mechanic through engine
overhaul process. Descriptions of processes of cleaning, inspection,
assembly and machine shop practice are included.
         Always refer to appropriate engine overhaul article in the
ENGINES section for complete overhaul procedures and specifications
for the vehicle being repaired.

         ENGINE IDENTIFICATION

         The engine may be identified from its Vehicle Identification
Number (VIN) stamped on a metal tab. Metal tab may be located in
different locations depending on manufacturer. Engine identification
number or serial number is located on cylinder block. Location varies
with manufacturer.

         INSPECTION PROCEDURES

         * PLEASE READ THIS FIRST *

NOTE:    Always refer to appropriate engine overhaul article in the
         ENGINES section for complete overhaul procedures and
         specifications for the vehicle being repaired.

         GENERAL

         Engine components must be inspected to meet manufacturer's
specifications and tolerances during overhaul. Proper dimensions and
tolerances must be met to obtain proper performance and maximum engine
life.
         Micrometers, depth gauges and dial indicator are used for
checking tolerances during engine overhaul. Magnaflux, Magnaglo, dye-
check, ultrasonic and x-ray inspection procedures are used for parts
inspection.

         MAGNETIC PARTICLE INSPECTION

         Magnaflux & Magnaglo
         Magnaflux is an inspection technique used to locate material
flaws and stress cracks. The part in question is subjected to a strong
magnetic field. The entire part, or a localized area, can be
magnetized. The part is coated with either a wet or dry material that
contains fine magnetic particles.