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durga8699 durga8699
wrote...
6 years ago
1. An engine is misfiring. A power balance test indicates that when the spark to cylinder #4 is grounded, there is no change in the engine speed. Technician A says that a burned valve is a possible cause. Technician B says that a defective cylinder #4 injector or spark plug wire could be the cause. Which technician is correct?

a. Technician A only
b. Technician B only
c. Both Technicians A and B
d. Neither Technician A nor B

2. Two technicians are discussing how to perform a road test to verify the customer’s concerns about noise from the engine. Technician A says that the owner should drive and the technician ride along to verify the problem. Technician B says that the vehicle should be driven next to a building to better hear engine noise as it bounces off the walls. Which technician is correct?

a. Technician A only
b. Technician B only
c. Both Technicians A and B
d. Neither Technician A nor B

3. A cylinder leakage (leak-down) test indicates 30% leakage, and air is heard coming out of the air inlet. Technician A says that this is a normal reading for a slightly worn engine. Technician B says that one or more intake valves are defective. Which technician is correct?

a. Technician A only
b. Technician B only
c. Both Technicians A and B
d. Neither Technician A nor B
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Replies
wrote...
Staff Member
6 years ago
1.  c
Explanation:
Technician A is correct because a burned valve will
cause the cylinder to produce less than normal power. Technician B is correct because a fault in either the injector or the spark plug wire can cause the cylinder to misfire.

2.c.

Explanation:
Technician A is correct because the customer can more easily drive the vehicle under the exact conditions, such as speed and throttle position, to create the noise concern. The technician can also concentrate on listening for the noise without having to worry about traffic conditions. Technician B is also correct because noise from the vehicle would tend to bounce off walls or buildings making engine noise easier to hear.

3.  b.

Explanation:
A leakage of 30% is excessive and if air is heard escaping from the engine air inlet, then one or more intake valves must be leaking. It is also possible that the cylinder being tested is not at TDC on the compression stroke. If the cylinder were at TDC of the exhaust stroke, both intake and exhaust valves would be open and air would also be heard coming from the tailpipe. Technician A is not correct because 30% leakage is too much for a slightly worn engine. Leakage should not exceed 20%.
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