Q45 V8-4494cc 4.5L DOHC (VH45) (1992)
Compression Check: Testing and Inspection
MEASUREMENT OF COMPRESSION PRESSURE
1. Warm up engine.
2. Turn ignition switch off.
3. Release fuel pressure. Refer to Powertrain Management; Fuel Delivery and Air Induction; Fuel Pressure Release.
4. Disconnect ignition coil with power transistor harness connectors, then remove ignition coils.
5. Remove all spark plugs.
6. Attach a compression tester to No. 1 cylinder.
7. Depress accelerator pedal fully to keep throttle valve wide open.
8. Crank engine and record highest gauge indication.
9. Repeat the measurement on each cylinder as shown above.
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Always use a fully-charged battery to obtain specified engine speed.
10. If compression in one or more cylinders is low:
a. Pour a small amount of engine oil into cylinders through spark plug holes.
b. Retest compression.
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If adding oil helps compression, piston rings may be worn or damaged. If so, replace piston rings after checking piston.
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If pressure stays low, a valve may be sticking or seating improperly. Inspect and repair valve and valve seat. If valve or valve seat is
damaged excessively, replace them.
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If compression stays low in two cylinders that are next to each other:
a. The cylinder head gasket may be leaking, or
b. Both cylinders may have valve component damage.