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.
1990 BMW 325is AutomaticFACTORY OEM SERVICE PROCEDURE
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 ) | |
Factory Service Tools
Use the Manual With the Right Hardware
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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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