BMW K100 LT User Manual

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EFI/Electronic ignition K100 2v
troubleshooting
Disclaimer:
This page is a guide but not a reference. I am not a professional but
only a K100 enthusiast with good knowledge of the bike.
Most of the information contained is this document was not available
anywhere on the Internet at the time this guide was written. After a
couple of month of research, I finally compiled this printable version.
The HTML version posted on the K100 forum has been viewed 5,000
times in 5 months. From all the feedback received, the information
published has been confirmed to be accurate.
Please use your own judgement when testing the electronic as I
CANNOT be responsible if you short or fry an electronic component.
This is an on going project and this file will be upgraded when new
information will be available. Please check it regularly.
Bertrand Vogel (Crazy frog)
This document should help you to understand how the LE-Jetronic and the electronic
ignition are working.
I would happily add your comments and experience to this page if they are relevant.
Click here to email me additional information
You don't need electronic knowledge but basic electrical knowledge
in order to test both units following the information on this page.
The following explanations and schematics are specific to the early K100 2 valves.
The 4 valves RS is different (Motronic) but the same principle applies to it.
The K75 shares the same technology and the principle is similar at the exception of an extra
coil.
First, you have done all the basic troubleshooting such as: checking the fuses, ignition
switch, kill switch, side stand switch (not applicable on early K100), transmission in
neutral, clutch in, starter connection, Fuel pump connector on the fuel tank, and battery
connections.
The ground connections are critical for the electrical system. The ground connection
between the battery (-) and the side of the transmission should be cleaned and tested.
the connection #9 on the frame should also be checked. (Remove the screw and clean
all the connectors)
Most of the starting failures are related to a corroded ground connector!
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Summary of Contents

Page 1

EFI/Electronic ignition K100 2v troubleshooting Disclaimer: This page is a guide but not a reference. I am not a professional but only a K100 enthus

Page 2

If your injector is leaking internally or failing to close fully the bike might run OK depending on just how bad the problem is. The way to chec

Page 3

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

Page 4 - Is the starter turning?

This airflow meter is factory sealed. If you don’t experience problems avoid breaking the seal on the cover. Dirt on the circuit board will affect th

Page 5

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

Page 6

The following graphic shows the different components and their connection to the EFI computer.

Page 7 - Fuel pressure regulator:

You can try to follow the full wiring diagram, but this is very confusing. To help you, I have detailed the wiring related to the EFI / Electronic i

Page 8

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

Page 9 - Fuel injectors:

Quick explanation of the principle: What's happening when you press the starter switch: The starter relay and Fuel Injection relay close, Hall

Page 10 - Air flow meter:

Water temperature sensor: The bike will not start if the water temperature is above the normal range of operation. A bad temperature sensor will sen

Page 11

Electronic ignition module (female connector): Electronic ignition module test: Pin # Function Testing mode type Expected value 1 Direct ground co

Page 12

First, here are a couple of schematics showing the location of the electrical components: Under tank connectors and ground Fuse box layout

Page 13

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 t

Page 14

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

Page 15 - Electronic ignition:

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.

Page 16

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

Page 17

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

Page 18 - Water temperature sensor:

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

Page 19

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

Page 20

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 t

Page 21

everything back and check the voltage at the injectors after each device is plugged back. Testing if the EFI computer is sending the "puls

Page 22

Testing the fuel pressure To test the system fuel pressure, install a manometer in parallel with the fuel pressure hose. If the fuel pump an

Page 23

Layout of electrical components (in the tray under the tank).

Page 24

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 ta

Page 25 - 7-8-9 are wrong

Now, let’s start the troubleshooting….. Is the starter turning? Here is a simplify schematic of the starter circuit

Page 26

If the engine is cranking, continue with this chart.

Page 27 - it is best is to use an LED

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 engin

Page 28

Fuel pressure regulator: Fuel pressure is sent from the pump to the Fuel injector rail. The fuel pressure regulator will keep a constant pressure i

Page 29

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 th

Page 30 - Bertrand Vogel (Crazy Frog)

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

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