Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET1986S10/T10 P/U 4WD L4-151 2.5LREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTTUNE-UP AND ENGINE PERFORMANCE CHECKSCOMPRESSION CHECKTESTING AND INSPECTION
1986 Chevrolet S10/T10 P/U 4WD L4-151 2.5L
Compression Check: Testing and Inspection
1986 Chevrolet S10/T10 P/U 4WD L4-151 2.5LSECTION Testing and Inspection
COMPRESSION CHECK
- Disconnect the primary terminal from the ignition coil.
- Remove all spark plugs.
- Block the throttle plate wide open.
- Make sure the battery is fully charged.
- Starting with the compression gauge at zero, crank the engine through four compression strokes (four "puffs").
- Make the compression check at each cylinder and record each reading.
- If some cylinders have low compression, inject 15 ml (one table spoon, or 3 squirts from a pump type oil can) of engine oil into the combustion chamber through the spark plug hole.
- See Specifications for minimum pressure and maximum variation. Specifications
Normal Compression: Compression builds up quickly and evenly to specified compression on each cylinder.
Piston Rings Leaking: Compression low on first stroke, tends to build up on following strokes, but does not reach normal. Improves considerably with addition of oil.
Valves Leaking: Low on first stroke. Does not tend to build up on following strokes. Does not improve much with addition of oil.
Head Gasket Leakage: If two adjacent cylinder have lower than normal compression, and injecting oil into cylinders does not increase the compression, the cause may be a head gasket leak between the cylinders.
- Disconnect the primary terminal from the ignition coil.
- Remove all spark plugs.
- Block the throttle plate wide open.
- Make sure the battery is fully charged.
- Starting with the compression gauge at zero, crank the engine through four compression strokes (four "puffs").
- Make the compression check at each cylinder and record each reading.
- If some cylinders have low compression, inject 15 ml (one table spoon, or 3 squirts from a pump type oil can) of engine oil into the combustion chamber through the spark plug hole.
- See Specifications for minimum pressure and maximum variation. Specifications
Normal Compression: Compression builds up quickly and evenly to specified compression on each cylinder.
Piston Rings Leaking: Compression low on first stroke, tends to build up on following strokes, but does not reach normal. Improves considerably with addition of oil.
Valves Leaking: Low on first stroke. Does not tend to build up on following strokes. Does not improve much with addition of oil.
Head Gasket Leakage: If two adjacent cylinder have lower than normal compression, and injecting oil into cylinders does not increase the compression, the cause may be a head gasket leak between the cylinders.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.