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 MANUALSFORD1999F 150 2WD PICKUP V6-4.2L VIN 2REPAIR AND DIAGNOSISMAINTENANCETUNE-UP AND ENGINE PERFORMANCE CHECKSCOMPRESSION CHECKTESTING AND INSPECTION
1999 Ford F 150 2WD Pickup V6-4.2L VIN 2
Compression Check: Testing and Inspection
1999 Ford F 150 2WD Pickup V6-4.2L VIN 2SECTION Testing and Inspection
AllData Editors Note - Ford does not provide a cranking pressure specification, only an acceptable range.
1. Make sure the oil in the crankcase is of the correct viscosity and at the proper level and that the battery is properly charged. Operate the vehicle until the engine is at normal operating temperature. Turn the ignition switch to the OFF position, then remove all the spark plugs.
2. Set the throttle plates in the wide-open position.
3. Install a compression gauge such as the Compression Tester in the No. 1 cylinder.
4. Install an auxiliary starter switch in the starting circuit. With the ignition switch in the OFF position, and using the auxiliary starter switch, crank the engine a minimum of five compression strokes and record the highest reading. Note the approximate number of compression strokes required to obtain the highest reading.
5. Repeat the test on each cylinder, cranking the engine approximately the same number of compression strokes.
The indicated compression pressures are considered within specification if the lowest reading cylinder is within 75 percent of the highest reading.
If one or more cylinders reads low, squirt approximately one tablespoon of Super Premium SAE 5W30 Motor Oil, X0-5W30-QSP meeting Ford specification WSS-M2C153-G on top of the pistons in the low-reading cylinders. Repeat the compression pressure check on these cylinders.
- If compression improves considerably, piston rings are faulty.
- If compression does not improve, valves are sticking or seating improperly.
- If two adjacent cylinders indicate low compression pressures and squirting oil on each piston does not increase compression, the head gasket may be leaking between cylinders. Engine oil or coolant in cylinders could result from this condition.
1. Make sure the oil in the crankcase is of the correct viscosity and at the proper level and that the battery is properly charged. Operate the vehicle until the engine is at normal operating temperature. Turn the ignition switch to the OFF position, then remove all the spark plugs.
2. Set the throttle plates in the wide-open position.
3. Install a compression gauge such as the Compression Tester in the No. 1 cylinder.
4. Install an auxiliary starter switch in the starting circuit. With the ignition switch in the OFF position, and using the auxiliary starter switch, crank the engine a minimum of five compression strokes and record the highest reading. Note the approximate number of compression strokes required to obtain the highest reading.
5. Repeat the test on each cylinder, cranking the engine approximately the same number of compression strokes.
Compression Pressure Limit Chart:
Compression Pressure Limit Chart:
The indicated compression pressures are considered within specification if the lowest reading cylinder is within 75 percent of the highest reading.
If one or more cylinders reads low, squirt approximately one tablespoon of Super Premium SAE 5W30 Motor Oil, X0-5W30-QSP meeting Ford specification WSS-M2C153-G on top of the pistons in the low-reading cylinders. Repeat the compression pressure check on these cylinders.
- If compression improves considerably, piston rings are faulty.
- If compression does not improve, valves are sticking or seating improperly.
- If two adjacent cylinders indicate low compression pressures and squirting oil on each piston does not increase compression, the head gasket may be leaking between cylinders. Engine oil or coolant in cylinders could result from this condition.
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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.