Troubleshooting the Fuel Injection System (BMW 5 Series E28)

Table of contents: L-Jetronic fuel injection system ↓ Fuel injection system Motronic ↓

L-Jetronic fuel injection system

Malfunction	Possible cause	Method of elimination
Engine (cold) starts with difficulty or does not start	Cold start injector or temperature switch is faulty	Check the cold start injector and temperature switch. Replace faulty components (see section Checking the operation and replacing the cold start injector and temperature switch)
	The fuel pump is not working	Check the fuel pump fuse and fuel pump relay (see sections Checking fuel pressure/fuel pump and Removal and installation the fuel pump, intermediate pump and fuel level sensor)
	The petal (valve) of the air flow meter is jammed or stuck in the open position	Inspect the air flow meter for damage (see section Checking the operation, removing and installing the air flow meter)
	Incorrect fuel pressure	Check the system pressure (see section Checking fuel pressure/fuel pump). Check the fuel pressure regulator (Section Checking the operation and replacing the fuel pressure regulator)
	Intake air leaks	Inspect all vacuum lines, air ducts, oil filter seals and dipstick seals
	Fuel injectors are clogged or not working	Check the fuel injectors (see section Checking the operation and replacing fuel injectors) and cable
	Coolant temperature sensor is faulty or there is a problem with the wiring	Check the coolant temperature sensor (see chapter Engine management and emission control systems, Chapter Checking fuel pressure/fuel pump)
	Throttle position sensor (TPS) is not adjusted correctly	Check the TPS adjustment (see chapter Engine management and emission control systems, Chapter Information sensors)
	Incorrect ignition timing	Check the ignition timing (see chapter Ignition system). Check the vacuum ignition corrector
	Dirt or other inclusions in the fuel	Check the fuel and drain the tank if necessary
	ECU is faulty	Have the ECU checked by a dealer or other specialist
The engine (warmed up) starts with difficulty or does not start	Cold start injector leaking or permanently open	Check the cold start injector and temperature switch (see section Checking the operation and replacing the cold start injector and temperature switch)
	Incorrect fuel pressure	Check the fuel pump. Replace if necessary (see section Checking fuel pressure/fuel pump)
	Low residual fuel pressure	Check the residual fuel pressure. Replace the fuel pump or fuel accumulator if necessary (see section Checking the operation and replacing the fuel pressure regulator)
	Fuel leakage (loss)	Inspect fuel lines and fuel injectors for leaks. Repair leaks as directed (see chapter Power supply system)
	Coolant temperature sensor is faulty or there is a problem with the wiring	Check the coolant temperature sensor (see chapter Engine management and emission control systems, Chapter Information sensors)
	Gas plug in the fuel line (hot weather)	Check the fuel pressure (see section Checking fuel pressure/fuel pump)
	EVAP system malfunction (if applied)	Check the EVAP system (see chapter Engine management and emission control systems, Chapter Evaporative emission control system (EVAP))
	Incorrect ignition timing	Check the ignition timing (see chapter Ignition system). Check the vacuum ignition regulator
	ECU is faulty	Have the ECU checked by a dealer or other specialist
	Idle Speed Control System Malfunction	Check the idle air control valve (see section Checking the operation, adjusting and replacing the idle air stabilization valve)
The engine under load malfunctions and jerks	The fuel injector is clogged or faulty	Check the fuel injectors. Check for clogged fuel lines. Replace faulty injectors (see section Checking the operation and replacing fuel injectors)
	Incorrect fuel pressure	Check the fuel system pressure (see section Checking fuel pressure/fuel pump). Check the fuel pressure regulator (see section Checking the operation and replacing the fuel pressure regulator)
	Fuel leak(s)	Check for leaks in the fuel lines and fuel injectors (see chapter Power supply system)
	Engine maintenance	Adjust the engine (see chapter Routine car maintenance). Check the distributor cap, rotor, spark plug wires and spark plugs and replace any faulty components
	The petal (valve) of the air flow meter is jammed or stuck in the open position	Inspect the air flow meter for damage (see section Checking the operation, removing and installing the air flow meter)
	Intake air leak	Inspect all vacuum lines, air ducts, oil filter seals and dipstick seals
The engine has an unstable idle speed	The idle speed control valve is faulty	Check the idle air control valve (see section Checking the operation, adjusting and replacing the idle air stabilization valve)
	No power to the idle speed control valve	Check the idle speed control relay and wires (see chapter On-board electrical equipment system)
	The vacuum ignition regulator is faulty	Check the ignition vacuum regulator and the electronic ignition vacuum regulator relay
	The idle speed control unit is faulty	Have your dealer check the idle air control unit

Fuel injection system Motronic

In this system, if a failure occurs, the ECU stores a fault code in its memory. These codes can only be read by a BMW dealer, as special equipment is required. If the dealer performs at least an initial diagnostic of the faults, this will save time.

Malfunction	Possible cause	Method of elimination
Loss of power	The coolant temperature sensor is faulty or the wire to the sensor is broken	Check the coolant temperature sensor and wire. Correct the wire or replace the sensor if faulty (see chapter Engine management and emission control systems)
	Incorrect fuel pressure	Check the fuel pressure at the fuel pump and intermediate pump, if used (see section Checking fuel pressure/fuel pump)
	The throttle valve does not open fully	Check the accelerator cable adjustment to ensure the throttle valve is fully open.
	The throttle valve does not open fully	Adjust the cable if necessary (see section Checking, adjusting and replacing the accelerator cable)
Engine (cold) starts with difficulty or does not start	Cold start injector or temperature switch is faulty (only on early Motronic systems)	Check the cold start injector and temperature switch. Replace faulty components (see section Checking the operation and replacing the cold start injector and temperature switch)
	The fuel pump is not working	Check the fuel pump fuse and relay (see section Relieving pressure in the fuel injection system and Checking fuel pressure/fuel pump)
	The petal (valve) of the air flow meter is jammed or stuck in the open position	Inspect the air flow meter for damage (see section Checking the operation, removing and installing the air flow meter)
	Incorrect fuel pressure	Check the system pressure (see section Checking fuel pressure/fuel pump)
	Intake air leaks	Inspect all vacuum lines, air ducts, oil filter seals and dipstick seals
	Fuel injectors are clogged or not working	Check the fuel injectors (see section Checking the operation and replacing fuel injectors) and cable
	Coolant temperature sensor is faulty or there is a problem with the wiring	Check the coolant temperature sensor (see chapter Engine management and emission control systems, Chapter Information sensors)
	TPS is not adjusted correctly (throttle position sensor)	Check the TPS adjustment (see chapter Engine management and emission control systems, Chapter Information sensors)
	Dirt or other inclusions in the fuel	Check the fuel and drain it from the tank if necessary
	ECU is faulty	Have the ECU checked by a dealer or other specialist
	Crankshaft position signal is lost	The position sensor or flywheel is faulty, or the reference pin is missing
The engine (warmed up) starts with difficulty or does not start	Cold start injector leaking or constantly open (only on early Motronic systems)	Check the cold start injector and temperature switch (see section Checking the operation and replacing the cold start injector and temperature switch)
	Incorrect fuel pressure	Check the fuel pressure (see section Checking fuel pressure/fuel pump)
	Low residual fuel pressure	Check the residual pressure of the fuel system (see section Checking fuel pressure/fuel pump)
	Fuel leak(s)	Inspect fuel lines and injectors for leaks. Repair leaks if necessary
	Coolant temperature sensor is faulty or there is a problem with the wiring	Check the coolant temperature sensor (see chapter Engine management and emission control systems, Chapter Information sensors)
	Gas plug in the fuel line (hot weather)	Check the fuel pressure (see section Checking fuel pressure/fuel pump)
	EVAP system is faulty	Check the EVAP system (see chapter Engine management and emission control systems, Chapter Evaporative emission control system (EVAP))
	The idle speed control system is faulty	Have the ECU checked by a dealer or other specialist
	The oxygen sensor is faulty (where applied)	Check the idle air control valve (see section Checking the operation, adjusting and replacing the idle air stabilization valve)
	The oxygen sensor is faulty (where applied)	Check the oxygen sensor (see chapter Engine management and emission control systems, Chapter Information sensors)
The engine under load malfunctions and jerks	The fuel injector is clogged	Check the fuel injectors. Check the injector lines for patency. Replace faulty injectors (see section Checking the operation and replacing fuel injectors)
	Incorrect fuel pressure	Check the fuel system pressure (see section Checking fuel pressure/fuel pump). Check the fuel pressure regulator (see section Checking the operation and replacing the fuel pressure regulator)
	Fuel leak	Check fuel lines and injectors for leaks (see chapter Power supply system)
	Engine maintenance	Adjust the engine (see chapter Routine car maintenance). Check the distributor cap, rotor, spark plug wires and spark plugs and replace any faulty components
	The petal (valve) of the air flow meter is jammed or stuck in the open position	Inspect the air flow meter for damage (see section Checking the operation, removing and installing the air flow meter)
	Intake air leaks	Inspect all vacuum lines, air ducts, oil filter seals and dipstick seals
	Throttle position sensor (TPS) is not adjusted correctly	Check the TPS adjustment (see chapter Engine management and emission control systems)
Increased engine idle speed	The accelerator pedal, cable or throttle valve is stuck	Check for worn or broken components, kinked cables, or other damage. Replace any faulty components
Increased engine idle speed	Air leak in the throttle valve	Inspect the throttle valve and adjust or replace if necessary
Unstable engine idle speed	The idle speed control valve is faulty	Check the idle air control valve (see section Checking the operation, adjusting and replacing the idle air stabilization valve)
	No power to the idle speed control valve	Check the idle speed control relay and wires (see chapter On-board electrical equipment system)
	The idle speed control unit is faulty	Have your dealer check the idle air control unit
Increased fuel consumption	Cold start injector leaking (only early Motronic systems)	Check and, if necessary, replace the cold start injector (see section Checking the operation and replacing the cold start injector and temperature switch)
	The oxygen sensor is faulty (where applied)	Check the oxygen sensor (see chapter Engine management and emission control systems, Chapter Information sensors)
	Parking brake sticks/brakes drag	Check the parking brake/brake system (see chapter Brake system)
	Low tire pressure	Check your tire pressure

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