Engine Compression
- Deactivate fuel injection system by removing fuel pump relay before performing compression test. See FUEL PUMP RELAY LOCATION table.
- Ensure battery is fully charged. Remove all spark plugs. Check compression with engine at normal operating temperature, throttle fully open and engine at cranking speed.
FUEL PUMP RELAY LOCATION
| Application | Location |
|---|---|
| 325i, 325iC & 325iS | On Left Front Shock Tower (Center Relay On Bracket) |
| 525i, 535i & 735i | In relay box in right rear corner of engine compartment |
NOTE:
To help identify fuel pump relays, see WIRING DIAGRAMS
article.
COMPRESSION SPECIFICATIONS
| Application | Specification | |
|---|---|---|
| Compression Ratio | ||
| 325i, 325iC, 325iS & 525i | 8.8:1 | |
| All Others | 9.0:1 | |
| Compression Pressure | ||
| All Models | 142-156 psi (10-11 kg/cm2 ) | |