BMW K100 LT- Manuals

You reached the orange box and the result of your investigation points to the EFI system. How does it works? You may not be an electronic engineer, but after reading the remaining of this document you should have a pretty good knowledge of the system. 2 major factors influence the EFI computer: Air ...

Fuel pressure regulator: Fuel pressure is sent from the pump to the Fuel injector rail. The fuel pressure regulator will keep a constant pressure into the fuel injector rail. The fuel pressure regulator is located on the back of the fuel injection rail (not easy to access) and its depression is coll...

Idle switch The idle switch (Also called butterfly switch or throttle switch) is located at the end of the fuel injector rail. It wills cut-off the fuel injector when releasing the throttle. With this system, when decelerating (switch 1 close), the fuel injection is disabled until the rpm goes down ...

Fuel injectors: The 4 injectors all open and close at the same time when commanded to do so by the ECU. It's important to understand that the injectors do not really spray fuel, they are just valves that open and close. They are needle valves that plug a small hole when closed. They are opened by a ...

If your injector is leaking internally or failing to close fully the bi ke might run OK depending on just how bad the problem is. The way to check for this problem is simple. When you change spark plugs inspect them. If one or two are a lot blacker then the others you probably have a leaking injecto...

Air traverses the air filter and goes to the air flow sensor. When you open the throttle, the depression is moving the internal vane of the air flow meter and a bigger amount of air is sucked in by the engine. The movement of the vanes will turn a variable resistance. This variable resistance will t...

Now, let's get practical.... EFI and Electronic ignition components:

Or if you prefer, this simplified schematic of the wiring:

Quick explanation of the principle: What's happening when you press the starter switch: The starter relay and Fuel Injection relay close, Hall sensors get power. The FI relay energizes (+) the fuel pump, the idle switch, the injectors and the air flow meter. The LE-Jetronic receives (pin #4) the sig...

Water temperature sensor: The bike will not start if the water temperature is above the normal range of operation. A bad temperature sensor will send the wrong signal to the EFI. The water temperature sensor contains 2 resistors: 1 feeding the EFI and one feeding the temperature switching unit. One ...

Electronic ignition module (female connector): Electronic ignition module test: Pin # Function Testing mode type Expected value 1 Direct ground continuity with ground at the battery Ω .5 max. 2 power to Hall sensors control with ignition ON Volts 12v 3 Ground to Hall sensors continuity with ground a...

Hall sensors: The Hall sensors are known to fail when hot. They are rated to operate at a temperature between -40 to +160 degrees Celsius. If the bike has a problem only when hot, warm up the sensors with a hair dryer and test them at different temperatures. WARNING: On the next test, never substitu...

Here is how to test the sensors. Any good sensor should light the LED until something metallic, like a feeler gauge, is introduced in to the sensors gap, the LED will then go out. Any sensor that doesn't light the LED or doesn't go out when the sensor gap is obstructed is defective . R bikes and K b...

volts are produced at the high voltage terminal, not enough to actually cause a spark. The actual spark is generated when the breaker contacts open . Much smaller coils are used and in the case of the K100. One coil is servicing two spark plugs (These coil s put off about 20kv) . I t is called a was...

Spark plugs and ignition wires: I have read on other forums people finding after market ignition wires and caps. This could be a big money saver, but it can also be a source of concern if you don’t pay attention to the following points: The K100 is originally fitted with Bosch X5DC (or can be fitted...

Electronic Fuel Injection . Here is a picture of the Electronic Fuel injection module female connector where the testing has to be done: Electronic Fuel Injection module (female connector)

LE-Jetronic (EFI) test: Pin # Function Testing mode type expected value 1 info on engine rpm When starter is running Volts ~ 10 to 20mv 2 Idle switch (idle) Ignition ON, FI relay ON, throttle OFF Volts -- 12v 3 Idle switch (full throttle) Ignition ON, FI relay ON, throttle full Volts -- 12v 4 starte...

Test of the air temperature sensor in the air flow meter: You will notice that the resistance decreases when the temperature rises. The value of the resistance is decreasing by a very small value (1Ω to 2Ω) for each difference of 1 degree. Here is how the thermi-resistor is tested: I placed the remo...

Testing the electrical power at the fuel injectors: Because of the injection time varying from 1.5ms to 9ms., it is best is to use an LED to test the EFI computer output. A cheap regular LED should work for this purpose but they are rated for 3.3v/20mA. A resistance would have to be installed in ser...

everything back and check the voltage at the injectors after each device is plugged back. Testing if the EFI computer is sending the "pulsing" negative to the fuel injectors: (The test of the EFI relay has to be conducted first) When you are pushing the starter button, you should get one pul...

Testing the fuel pressure To test the system fuel pressure, install a manometer in parallel with the fuel pressure hose. If the fuel pump and the external pressure regulator are working correctly, you should read close to 36psi on the gauge Testing the pump pressure

Testing the pump and fuel pressure regulator To test the fuel pressure output of the pump, install the manometer right at the pressure port of the tank. You should read about 65 psi. The internal relief valve of the pump should keep the pressure to this value. A lower value reflects a bad fuel pump ...