Basic Troubleshooting
25
PCV testing
The PCV (Positive Crankcase Ventilation) valve is
located in the engine block and allows the crankcase pres-
sure to escape.
Leakage and blockage are the two failure modes for a
PCV system. Either mode will cause crankcase pressure
to build-up, though the effects of a blocked PCV are gener-
ally more dramatic. Increased case pressure will result in
oil entering the combustion chamber.
NOTE: The PCV chamber is vented to the air filter through
a molded rubber hose. The rubber hose directs
crankcase fumes to a covered duct within the air
filter housing. See Figure 2.4.
To measure the crankcase pressure:
1. Remove the dipstick.
2. Attach a manometer to the dipstick tube.
3. Start the engine.
4. Read the measurement on the manometer. See Fig-
ure 2.5.
NOTE: Less than (between zero and -1”) (-2.54cm) of
water is a typical reading.
NOTE: Experimentation by MTD’s Training and Education
Department has revealed the following character-
istics of MTD engines:
• A leaky PCV system will not build-up substantial
case pressure.
• A leaky PCV system will allow the engine to ingest
contaminants through the system, accelerating
engine wear.
• A blocked PCV system will allow crankcase pres-
sure to build very rapidly. Noticeable oil fumes will
be evident in the exhaust within several minutes of
normal operation.
Figure 2.4
Breather
Breather hose
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