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.
1989 BMW 635CSi AutomaticFACTORY OEM SERVICE PROCEDURE
Engine Compression
- Deactivate fuel injection system by removing fuel pump relay before performing compression test. On 3 series vehicles, fuel pump relay is on bracket on left front shock tower (center relay on bracket). On 5 and 7 series vehicles, fuel pump relay is in relay box in right rear corner of engine compartment. On 635CSi vehicles, fuel pump relay is on left side of engine compartment, attached to outside of relay/fuse box.NOTE: See L - WIRING DIAGRAMS to help identify relays.
- Ensure battery is fully charged. Check compression with engine at normal operating temperature, throttle fully open, and engine at cranking speed.
COMPRESSION SPECIFICATIONS
| Application | Specification | |
|---|---|---|
| Compression Ratio | ||
| 325i, 325iC, 325iS & 525i | 8.8:1 | |
| All Others | 9.0:1 | |
| Compression Pressure | 142-156 psi (10-11 kg/cm2 ) | |
Factory Service Tools
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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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