Mechanical Inspection: Compression
WARNING:
DO NOT use ignition switch to crank engine during compression test on fuel injected vehicles, use a remote starter switch. Fuel injectors on many models are triggered by ignition switch during cranking mode, which can create a fire hazard or contaminate the engine's oiling system.
NOTE:
Before checking engine compression test ensure engine oil and coolant level is correct, battery is fully charged and starter motor is operating properly.
Check engine mechanical condition using a compression gauge, vacuum gauge or an engine analyzer. See engine analyzer manual for specific instructions. Ensure engine is at normal operating temperature. Engine cranking speed must be at least 250 RPM during compression test. Check compression pressure at all cylinders as follow:
- Start engine and allow it to reach normal operating temperature. Turn ignition switch to LOCK position.
- Disable fuel injectors by disconnecting fuel injector main harness connectors. See Fig 1 . Remove ignition coils and spark plugs. See SPARK PLUGS & IGNITION COIL ASSEMBLY under IGNITION SYSTEM in REMOVAL & INSTALLATION article.
- Install compression gauge into spark plug hole. See Fig 2 . For vehicles equipped with (M/T) depress clutch pedal. Depress accelerator pedal to fully open throttle position. Crank engine and read the highest pressure on compression gauge. Compression should be within specification. See COMPRESSION SPECIFICATIONS table. Carry out this step for each cylinder.
COMPRESSION SPECIFICATIONS
| Application | Specification | ||||||
|---|---|---|---|---|---|---|---|
| Compression Pressure (1) | |||||||
| Aerio | |||||||
| Standard | 199 psi (14.0 kg/cm2 ) | ||||||
| Limit | (2) 170 psi (12.0 kg/cm2 ) | ||||||
| Grand Vitara & XL-7 | |||||||
| Standard | 199-228 psi (14.0-16.0 kg/cm2 ) | ||||||
| Limit | (2) 185 psi (13.0 kg/cm2 ) | ||||||
| Vitara | |||||||
| Standard | 199 psi (14.0 kg/cm2 ) | ||||||
| Limit | (2) 170 psi (12.0 kg/cm2 ) | ||||||
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