Mechanical Inspection: Compression

Deactivate fuel injection system by removing Digital Motor Electronics (DME) master relay and fuel pump relay before performing compression test. See DME & FUEL PUMP RELAY LOCATION table. Ensure battery is fully charged.
Ensure engine coolant temperature does not exceed 95°F (35°C). Turn 2 fasteners on electric lead cover 90 degrees, and remove electric lead cover. Repeat for other cover on V8 engines. Disconnect spark plug connectors.
Using 16-mm Socket (12-1-171) and Torque Limiter (12-1-172), remove spark plugs. Use Pressure Gauge (11-0-162), Test Adapter (11-0-166) and Tube Extension (11-0-167) to check compression pressure. See ENGINE COMPRESSION SPECIFICATIONS table.

ENGINE COMPRESSION SPECIFICATIONS ⁽¹⁾

Application

Pressure: psi (kg/cm² )

Normal Compression Pressure

142-156 (10-11)

⁽¹⁾	Maximum variation between cylinders and minimum compression pressure specifications are not available from manufacturer.

DME & FUEL PUMP RELAY LOCATION

Application

Location

325i, 325iC & 325is

⁽¹⁾ Behind Cover, Along Engine Bay Firewall

⁽¹⁾	First relay (viewed from left to right) after ground wire is fuel pump relay followed by Digital Motor Electronics (DME) master relay.