400 Auto Engine Performance and Driveability
Copyright by Goodheart-Willcox Co., Inc.
Most emission control components are relatively easy
to replace. The usual procedure is to remove electrical
connectors and vacuum lines, any brackets, and the part.
Always compare the old and new parts. Some emission
control components, such as EGR valves and components
in the air injection system, may require new gaskets.
Installation of a new part is the reverse of removal.
Always recheck system operation after any new parts
are installed. Road test the vehicle. Do not clear trouble
codes if the vehicle must pass an emissions test. Doing so
will clear any monitors that have been set. If necessary,
perform a drive cycle.
Review Questions—Chapter 18
Answer the following questions using the information
provided in this chapter.
1. During a(n) _____ test, the vehicle is operated on a
dynamometer.
2. When preparing a vehicle for an emissions test, at
what temperature should the engine be?
3. To reduce the chance of fi re, the evaporative
emissions system should be pressurized only
with _____.
4. Most EGR solenoids are normally ______ types and
are ______ by an electrical signal from the ECM.
5. On a properly operating vacuum EGR position
sensor, the electrical value will vary as ______ varies.
6. The position of an electronic EGR valve can be read
with a(n) _____.
7. Air pump operation can be checked only when the
engine is _____.
8. With the engine at normal operating temperature, the
fl ap in the thermostatic air cleaner is closed. What
does this signify?
9. A rattling noise is heard from the PCV valve when it
is shaken. What does this tell the technician?
10. List two symptoms of a restricted exhaust system.
ASE Certifi cation-Type Questions
1. Technician A says that a dynamometer is not needed
for an enhanced emissions test. Technician B says
that securing devices, such as wheel chocks or
snubbing chains, must be installed before operating
a vehicle on a dynamometer. Who is correct?
(A) A only.
(B) B only.
(C) Both A & B.
(D) Neither A nor B.
2. Technician A says that most enhanced emissions
tests last longer than four minutes. Technician B says
that some testing systems stop the test early if the
emissions are very low or very high. Who is correct?
(A) A only.
(B) B only.
(C) Both A & B.
(D) Neither A nor B.
3. Technician A says that a vacuum gauge can be
used to check for an exhaust system restriction.
Technician B says that a pressure gauge can be used
to check for an exhaust system restriction. Who is
correct?
(A) A only.
(B) B only.
(C) Both A & B.
(D) Neither A nor B.
4. Technician A says that PCV valves can be checked
with the engine running. Technician B says that many
PCV valves cannot be replaced. Who is correct?
(A) A only.
(B) B only.
(C) Both A & B.
(D) Neither A nor B.
5. The evaporative emission control canister is saturated
with fuel. Technician A says that a defective canister
purge valve could cause the problem. Technician B
says that the saturated canister could cause HC and
CO levels to be excessively high. Who is correct?
(A) A only.
(B) B only.
(C) Both A & B.
(D) Neither A nor B.
6. Flow restrictions in the evaporative emission control
system can be caused by any of the following, except:
(A) clogged canister fi lter.
(B) inoperative fl ow control valve(s).
(C) disconnected hoses.
(D) defective hoses.