Engine Compression

WARNING: This page is about a different car, the 1995 BMW 525iT, 1995 BMW 525i, 1995 BMW 325is, and 1995 BMW 325i. However, it is still accessible from the selected car via links, so may be relevant.

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 86°F (30°C). Remove oil filler cap. Remove 2 nut covers and nuts securing cylinder head cover(s). Remove cylinder head cover(s). Disconnect ignition coil connectors.
Remove ignition coils. 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 COMPRESSION SPECIFICATIONS table.

COMPRESSION SPECIFICATIONS

Application	Specification
Compression Ratio	10.0:1
Compression Pressure	142-156 psi (10-11 kg/cm² )

DME & FUEL PUMP RELAY LOCATION

Application

Location

325i, 325iC & 325is

⁽¹⁾ Behind Cover, Along Engine Compartment Firewall

525i & 525iT

⁽²⁾ Right Inner Fender Panel Of Engine Compartment

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

⁽²⁾	First relay (viewed from top to bottom) is Digital Motor Electronics (DME) master relay, followed by fuel pump relay and then oxygen sensor heater relay.