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.
Engine Compression
Warm engine to normal operating temperature. Check compression at cranking speed with throttle wide open and all spark plugs removed. On engines equipped with dual plug cylinders, remove exhaust side only. Ensure crankcase is at correct level and oil is correct viscosity. With compression gauge installed, use remote starter to crank engine.
Crank engine 5 revolutions (minimum) and record highest reading. Repeat procedure for all cylinders using approximately same number of revolutions. Lowest compression reading should not be less than 75 percent of highest compression reading. Cylinder compression readings should not be less than 100 psi (7 kg/cm2 ).
| Application | Compression Ratio | ||
|---|---|---|---|
| 4.6L | 9.0:1 | ||
| 5.0L Except MA (1) | 8.9:1 | ||
| 5.0L MA (1) | 9.0:1 | ||
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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.
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