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Mechanical Inspection: Compression

  1. 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.
  2. 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. Disconnect spark plug connectors.
  3. 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

Application psi (kg/cm2 )
Normal Compression Pressure (1) 142-156 (10-11)
(1) Maximum variation between cylinders and minimum compression pressure specifications not available at time of publication.
DME & FUEL PUMP RELAY LOCATION

Application Location
318i, 318is & 318ti (1) Behind Cover, Along Engine Compartment Firewall
(1) First relay (viewed from left to right) after ground wire is fuel pump relay followed by Digital Motor Electronics (DME) master relay.
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