FAILURE DIAGNOSIS
TNV DI Service Manual
1-219
Troubleshooting By Measuring Compression Pressure
TROUBLESHOOTING BY
MEASURING COMPRESSION
PRESSURE
Compression pressure drop is one of the major
causes of increasing blow-by gas (engine oil
contamination or increased engine oil consumption
as a resultant phenomenon) or starting failure. The
compression pressure is affected by the following
factors:
1. Degree of clearance between the piston and
cylinder
2. Degree of clearance at the intake / exhaust
valve seat
3. Gas leak from the nozzle gasket or cylinder
head gasket
The pressure will drop due to increased parts wear.
Pressure drop reduces the durability of the engine.
A pressure drop may also be caused by a
scratched cylinder or piston, dust entrance from the
dirty air cleaner element or a worn or broken piston
ring. Measure the compression pressure to
determine the condition of the engine.
Compression Pressure Measurement
Method
1. Warm up the engine.
2. Stop the engine. Remove the high-pressure fuel
injection lines as an assembly from the engine.
For engines with 2 valve cylinder heads
3. Remove the fuel injector from the cylinder to be
measured. See Removal of Fuel Injectors on
page 7-35.
For engines with 4 valve cylinder heads
4. Remove the valve cover assembly. See
Removal of Valve Cover on page 6-52. Remove
the fuel injector from the cylinder to be tested.
See Removal of Fuel Injectors on page 7-35.
5. Turn off the fuel supply valve in the fuel supply
line. Disconnect the fuel injection pump stop
solenoid at the connector. This prevents the fuel
injection pump from injecting fuel during
compression testing.
6. Before installing the compression gauge
((Figure 1-1, (1)) 2 valve engine,
(Figure 1-2, (1)) 4 valve engine) adapter, crank
the engine with the stop solenoid disconnected
for a few seconds to clear the cylinder of any
residual fuel.
7. Install a nozzle seat at the tip end of the
compression gauge adapter. Install the
compression gauge and the compression
gauge adapter at the cylinder to be measured.
8. Crank the engine until the compression gauge
reading is stabilized.
Figure 1-1
CAUTION
Remove or install the high-pressure fuel
injection lines as an assembly whenever
possible. Disassembling the
high-pressure fuel injection lines from
the retainers or bending any of the fuel
lines will make it difficult to reinstall the
fuel lines.
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