Troubleshooting Troubleshooting – Engine – 2.5L NA Estimated reading: 5 minutes Contributors Overview This troubleshooting guide is tailored for the Porsche 944 3.0L S2 (1989–1991) to diagnose and repair engine starting, running, and lubrication system issues. It focuses on common problems such as failure to start, rough idling, and oil pressure issues, ensuring optimal performance for the S2’s advanced engine and alloy control arm configuration. Proper diagnosis is critical to maintaining the S2’s high-performance capabilities. Engine Will Not Rotate If the engine does not turn over, the issue is typically related to the electrical or starter system. Below are possible causes and checks specific to the 3.0L S2. Possible Causes Checks Discharged or Faulty Battery Check battery voltage and connections (Refer to ELECT-15). Battery Terminals Loose or Corroded Inspect and clean terminals (Refer to ELECT-15). Bad Starter Motor or Starter Solenoid Test starter and solenoid (Refer to ELECT-16). Bad Ignition Switch Test ignition switch (Refer to ELECT-17). Broken or Loose Wiring in Starter Circuit Inspect wiring (Refer to ELECT-17). Broken Teeth on Starter Pinion or Flywheel Remove starter and inspect pinion teeth. Roll engine using a 24 mm socket and ratchet to check flywheel. Engine Will Rotate But Will Not Start (Fire) If the engine cranks but does not start, the issue is likely due to lack of fuel or spark. Use a fuel pressure gauge, spark tester, and multimeter for diagnosis. Testing for Lack of Fuel Connect a fuel pressure gauge to the fuel rail. Attempt to start the vehicle while observing the gauge. If pressure rises, compare to specifications (Refer to FUEL-01). If no pressure increase, troubleshoot fuel pump (Refer to FUEL-16). For low or slow pressure, check other fuel system components (Refer to FUEL-16). Testing for Lack of Spark Remove fuel pump fuse to prevent fuel flow during testing. Disconnect a plug wire and connect a spark tester in series with the spark plug. Crank the engine and observe for spark in the tester. If no spark at the plug, test the main lead from the ignition coil to the distributor using a spark tester. If spark is present at the coil but not at the plug, replace the distributor cap/rotor. If no spark at the coil, proceed to ignition troubleshooting (Refer to IGN-04). Engine Is Difficult to Start When Cold Possible Causes Checks DME Temperature Sensor Check sensor resistance (Refer to ELECT-19). Fuel System Vapor Lock Perform fuel pressure and leakdown test (Refer to FUEL-01). If it fails, diagnose cause (Refer to FUEL-17). Fuel Pressure Too High Disconnect one fuel injector connector and attempt to start. If it starts, replace the Fuel Pressure Regulator. Speed/Reference Sensors Wiggle sensor wires, clean sensor ends, and check clearance (Refer to IGN-02). DME Computer Tap DME while cranking. If it starts, repair solder joints. Inspect for bad joints (Refer to DME-05). Engine Is Difficult to Start When Hot Possible Causes Checks DME/Fuel Pump Relay Test with a jumper during hot start issue (Refer to FUEL-05). Fuel System Vapor Lock Perform fuel pressure and leakdown test (Refer to FUEL-01). If it fails, diagnose cause (Refer to FUEL-17). Speed/Reference Sensors Wiggle sensor wires, clean sensor ends, and check clearance (Refer to IGN-02). DME Computer Tap DME while cranking. If it starts, repair solder joints. Inspect for bad joints (Refer to DME-05). Engine Idles Rough When Cold Possible Causes Checks DME Temperature Sensor Check cold resistance (Refer to ELECT-19). Vacuum Leak Inspect hoses downstream of the AFM. Engine Idle Surges Possible Causes Checks Idle Stabilizer/Auxiliary Air Valve Clamp line to intake manifold. If idle stabilizes, clean or replace the valve. Vacuum Leak Inspect hoses downstream of the AFM. Throttle Body Butterfly Sticking Clean throttle body around butterfly valve. Engine Shudders at Idle Possible Causes Checks Engine Idle Set Too Low Check and reset idle (Refer to FUEL-08). Engine Hesitates or Stumbles During Acceleration Possible Causes Checks Dead Spot in Air Flow Meter (AFM) Test AFM (Refer to ELECT-19). Vacuum Leak Pressurize intake manifold with 10 psi compressed air and listen for leaks. Spark Plugs Fouled Check spark plug condition (Refer to ENG-18). Engine Misses Possible Causes Checks Bad Spark Plug Wires Check for arcing in a dark area. Cracked Distributor Cap Inspect cap condition. Faulty Spark Plug Inspect plugs for damage or wear (Refer to ENG-18). Vacuum Leak Pressurize intake manifold and listen for leaks. Clogged Fuel Filter Replace filter (Refer to FUEL-03). DME Computer Inspect for bad solder joints (Refer to DME-05). Engine Backfires Possible Causes Checks Faulty Ignition System Check spark plug wires and plugs. Vacuum Leak Pressurize intake manifold and listen for leaks. DME Computer Inspect for bad solder joints (Refer to DME-05). Engine Oil Pressure Low Possible Causes Checks Oil Level Low Check oil level and top off. Verify low oil level light (Refer to LUBE-03). Crankshaft Pulley Bolt Loose Check torque (155 ft-lbs) (Refer to LUBE-03). Bad Oil Pressure Sending Unit Test sending unit (Refer to LUBE-03, ELECT-19). Oil Pump Lost Prime Remove oil filter, pour oil into filter housing while turning crankshaft counterclockwise, then reinstall filter and check pressure (Refer to LUBE-03). Bad or Stuck Open Oil Pressure Relief Valve Remove, clean, and reinstall valve, ensuring no binding. Worn Engine Bearings Check pressure when warmed up (Refer to LUBE-03). Broken Oil Pump Pickup Tube Remove oil pan to inspect (last resort). Bad Oil Pump Remove and inspect pump gears. Engine Oil Pressure High Possible Causes Checks Bad Oil Pressure Sending Unit Test sending unit (Refer to LUBE-03, ELECT-19). Stuck Closed Oil Pressure Relief Valve Remove, clean, and reinstall valve, ensuring no binding. Blocked Oil Passage Check for tapping from hydraulic lifters or oil leaks at cam assembly gasket. Sources Clark’s Garage Pelican Parts Porsche 944 Workshop Manuals YouTube Tagged:Engine Troubleshooting Troubleshooting – Engine – 2.5L NA - PreviousTroubleshooting – Electrical (including Instruments) – 2.5L NANext - Troubleshooting – Engine – 2.5L NATroubleshooting – Fuel System – 2.5L NA
