L-Jetronic fuel injection system
Malfunction | Possible reason | Remedy |
Engine (cold) hard to start or not to start | Faulty cold start injector or temperature switch | Check cold start injector and temperature switch. Replace defective components (see Section Function test and replacement of cold start injector and temperature switch) |
Fuel pump not working | Check fuel pump fuse and fuel pump relay (see Sections Fuel/Fuel Pump Pressure Check and Removal and installation of the fuel pump, intermediate pump and fuel level sensor) | |
Jamming or sticking in the open position of the petal (valve) air flow meter | Inspect the air flow meter for damage (see Section Functional check, removal and installation of the air flow meter) | |
Incorrect fuel pressure | Check system pressure (see Section Fuel/Fuel Pump Pressure Check). Check fuel pressure regulator (Chapter Check of functioning and replacement of a regulator of pressure of fuel) | |
Intake air leaks | Inspect all vacuum lines, air ducts, oil filter and oil dipstick seals | |
Clogged or not working fuel injectors | Check fuel injectors (see Section Check of functioning and replacement of fuel injectors) and cable | |
Faulty coolant temperature sensor or wiring problems | Check coolant temperature sensor (see chapter Engine management and emission control systems, Chapter Fuel/Fuel Pump Pressure Check) | |
Throttle position sensor incorrectly adjusted (TPS) | Check TPS adjustment (see chapter Engine management and emission control systems, Chapter Information sensors) | |
Wrong ignition timing | Check ignition timing (see chapter Ignition system). Check Vacuum Ignition Corrector | |
Dirt or other inclusions in the fuel | Check the fuel and, if necessary, drain the fuel from the tank | |
Faulty ECU | Have the ECU checked by a dealer or other specialist | |
Engine (warmed up) hard to start or not to start | Cold start injector leak or permanently open | Check cold start injector and temperature switch (see Section Function test and replacement of cold start injector and temperature switch) |
Incorrect fuel pressure | Check fuel pump (s). Replace if necessary (see Section Fuel/Fuel Pump Pressure Check) | |
Slight residual fuel pressure | Check residual fuel pressure. Replace fuel pump or fuel accumulator if necessary (see Section Check of functioning and replacement of a regulator of pressure of fuel) | |
A leak (cliffs) fuel | Inspect fuel lines and fuel injectors for leaks. Repair leaks as directed (see chapter Supply system) | |
Faulty coolant temperature sensor or wiring problem | Check coolant temperature sensor (see chapter Engine management and emission control systems, Chapter Information sensors) | |
Gas plug in the fuel line (hot weather) | Check fuel pressure (see Section Fuel/Fuel Pump Pressure Check) | |
EVAP system malfunction (if applied) | Check the EVAP system (see chapter Engine management and emission control systems, Chapter Gasoline vapor recovery system (EVAP)) | |
Wrong ignition timing | Check ignition timing (see chapter Ignition system). Check Vacuum Ignition Regulator | |
Faulty ECU | Have the ECU checked by a dealer or other specialist | |
Malfunction of the idle control system | Check idle air control valve (see Section Check of functioning, adjustment and replacement of the air valve of stabilization of idling) | |
The engine under load falters and twitches | Clogged or defective fuel injector | Check fuel injectors. Check for clogged fuel lines. Replace faulty injectors (see Section Check of functioning and replacement of fuel injectors) |
Incorrect fuel pressure | Check the pressure in the fuel system (see Section Fuel/Fuel Pump Pressure Check). Check fuel pressure regulator (see Section Check of functioning and replacement of a regulator of pressure of fuel) | |
A leak (leaks) fuel | Check for leaks in fuel lines and fuel injectors (see chapter Supply system) | |
Engine maintenance | Adjust the engine (see chapter Car maintenance). Check the distributor cap, runner, high voltage wires and spark plugs and replace any faulty components | |
Jamming or sticking in the open position of the petal (valve) air flow meter | Inspect for damage to the airflow meter (see Section Functional check, removal and installation of the air flow meter) | |
Intake air leak | Inspect all vacuum lines, air ducts, oil filter and dipstick seals | |
Engine has erratic idle speed | Faulty idle air control valve | Check idle air control valve (see Section Check of functioning, adjustment and replacement of the air valve of stabilization of idling) |
No power to the idle control valve | Check idle speed relay and wires (see chapter Onboard electrical system) | |
Faulty vacuum ignition regulator | Check Vacuum Ignition Control and Vacuum Ignition Control Electronic Relay | |
Faulty idle control unit | Have your dealer check the idle speed control unit |
Motronic fuel injection system
In this system, in the event of a failure, the ECU stores a fault code in memory. These codes can only be read by a BMW dealer as special equipment is required. Having the dealer perform at least initial troubleshooting can save time.
Malfunction | Possible reason | Remedy |
Loss of power | Faulty coolant temperature sensor or broken wire to the sensor | Check coolant temperature sensor and wire. Fix wire or replace sensor if defective (see chapter Engine management and emission control systems) |
Incorrect fuel pressure | Check fuel pressure at fuel pump and intermediate pump if applicable (see Section Fuel/Fuel Pump Pressure Check) | |
Throttle valve does not open fully | Check the throttle cable adjustment to make sure the throttle valve is fully open. | |
Adjust cable if necessary (see Section Checking, adjusting and replacing the accelerator cable) | ||
Engine (cold) hard to start or won't start | Faulty cold start injector or temperature switch (only on early Motronic systems) | Check cold start injector and temperature switch. Replace defective components (see Section Function test and replacement of cold start injector and temperature switch) |
Fuel pump not working | Check fuel pump fuse and relay (see Section Relieving pressure in the fuel injection system and Fuel/Fuel Pump Pressure Check) | |
Jamming or sticking in the open position of the petal (valve) air flow meter | Inspect for damage to the airflow meter (see Section Functional check, removal and installation of the air flow meter) | |
Incorrect fuel pressure | Check system pressure (see Section Fuel/Fuel Pump Pressure Check) | |
Intake air leaks | Inspect all vacuum lines, air ducts, oil filter and oil dipstick seals | |
Clogged or not working fuel injectors | Check fuel injectors (see Section Check of functioning and replacement of fuel injectors) and cable | |
Faulty coolant temperature sensor or wiring problem | Check coolant temperature sensor (see chapter Engine management and emission control systems, Chapter Information sensors) | |
TPS misadjusted (throttle position sensor) | Check TPS adjustment (see chapter Engine management and emission control systems, Chapter Information sensors) | |
Dirt or other inclusions in the fuel | Check the fuel and, if necessary, drain it from the tank | |
Faulty ECU | Have the ECU checked by a dealer or other specialist | |
Lost crankshaft position signal | Defective encoder or handwheel, or missing reference pin | |
Engine (warmed up) hard to start or won't start | Leaking or permanently open cold start injector (only on early Motronic systems) | Check cold start injector and temperature switch (see Section Function test and replacement of cold start injector and temperature switch) |
Incorrect fuel pressure | Check fuel pressure (see Section Fuel/Fuel Pump Pressure Check) | |
Slight residual fuel pressure | Check the residual pressure of the fuel system (see Section Checking fuel pressure/fuel pump) | |
A leak (And) fuel | Inspect fuel lines and injectors for leaks. Repair leaks if necessary | |
Faulty coolant temperature sensor or wiring problem | Check coolant temperature sensor (see chapter Engine management and emission control systems, Chapter Information sensors) | |
Gas plug in the fuel line (hot weather) | Check fuel pressure (see Section Fuel/Fuel Pump Pressure Check) | |
Faulty EVAP system | Check the EVAP system (see chapter Engine management and emission control systems, Chapter Gasoline vapor recovery system (EVAP)) | |
Faulty idle control system | Have the ECU checked by a dealer or other specialist | |
Faulty oxygen sensor (where applied) | Check idle air control valve (see Section Check of functioning, adjustment and replacement of the air valve of stabilization of idling) | |
Check oxygen sensor (see chapter Engine management and emission control systems, Chapter Information sensors) | ||
The engine under load falters and twitches | Clogged fuel injector | Check fuel injectors. Check the patency of the injector lines. Replace faulty injectors (see Section Check of functioning and replacement of fuel injectors) |
Incorrect fuel pressure | Check fuel system pressure (see Section Fuel/Fuel Pump Pressure Check). Check fuel pressure regulator (see Section Check of functioning and replacement of a regulator of pressure of fuel) | |
A leak (And) fuel | Check fuel lines and injectors for leaks (see chapter Supply system) | |
Engine maintenance | Adjust the engine (see chapter Car maintenance). Check the distributor cap, runner, high voltage wires and spark plugs and replace any faulty components | |
Jamming or sticking in the open position of the petal (valve) air flow meter | Inspect for damage to the air flow meter (see Section Functional check, removal and installation of the air flow meter) | |
Intake air leaks | Inspect all vacuum lines, air ducts, oil filter and oil dipstick seals | |
Throttle position sensor incorrectly adjusted (TPS) | Check TPS adjustment (see chapter Engine management and emission control systems) | |
Increased engine idle | Stuck accelerator pedal, cable or throttle valve | Check for worn or broken components, twisted cable or other damage. Replace defective components |
Air leak in throttle valve | Inspect throttle valve and adjust or replace if necessary | |
Unstable engine idle | Faulty idle air control valve | Check idle air control valve (see Section Check of functioning, adjustment and replacement of the air valve of stabilization of idling) |
No power to the idle control valve | Check idle speed relay and wires (see chapter Onboard electrical system) | |
Faulty idle control unit | Have your dealer check the idle speed control unit | |
Increased fuel consumption | cold start injector leaking (only early Motronic systems) | Check and, if necessary, replace the cold start injector (see Section Function test and replacement of cold start injector and temperature switch) |
Faulty oxygen sensor (where applied) | Check oxygen sensor (see chapter Engine management and emission control systems, Chapter Information sensors) | |
Parking brake sticks/brakes slow down | Check parking brake/brake system (see chapter Brake system) | |
Low tire pressure | Check tire pressure |