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
Check engine compression with engine at normal operating temperature at specified cranking speed, all spark plugs removed (on dual plugs, remove exhaust side only) and throttle wide open. The DME master relay and/or fuel pump MUST be pulled out for compression test. See ADJUSTMENTS article in the ENGINE PERFORMANCE Section for additional information.
| Application | Specification | |
|---|---|---|
| Compression Ratio | ||
| 325i, 325iC & 325is | 8.8:1 | |
| 525i | 8.8:1 | |
| 535i, 735i & 735iL | 9.0:1 | |
| Compression Pressure | 142-156 psi (10-11 kg/cm2 ) | |
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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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