Basic principles for troubleshooting of EFI motorcycles

The EFI system is a sophisticated and complex system that has a great impact on the 
engine's running performance. Whether it is the ECU, control circuit or any other sensor or actuator failure, it will affect the engine to some extent. Startability, operational stability, 
power, economy, etc.

The cause of the EFI engine not working or working abnormally may be the electronic 
control system, or it may be a problem other than the electronic control system, or it may 
be mechanical; and the EFI system of different models often has a large Differences, the 
difficulty level of fault checking is also different, so it brings certain difficulties to the 
inspection and elimination of faults.

If we can follow some basic principles of EFI motorcycle fault diagnosis, the diagnosis and 
elimination of faults can be solved. The basic principles for troubleshooting the EFI 
motorcycle can be summarized as follows.

1、From outside and inside

In the event of an engine failure, first check for possible fault locations outside the 
This avoids the fact that it is a fault unrelated to the electronic 
control system, but it does a complicated and time-consuming inspection of the system's 
sensors, ECUs, actuators and circuits, ie the real fault may be easier to find but not found.

Taking the intake system as an example, the ECU mainly controls the fuel injection amount according to the air flow measured by the air flow meter or the intake manifold pressure 
measured by the intake pipe pressure sensor, so the intake system is not tightly sealed and the air leakage may cause the engine. The imbalance causes the idle speed to be unstable, the flameout, the power and the acceleration to deteriorate, and the impact on the system 
is much greater than that of the carburetor engine.
 
When diagnosing the failure of the intake system, first check and eliminate according to the basic diagnostic procedures without electronic control components; if the fault is still not 
eliminated, and confirm that the intake system has failed, first remove the air filter and 
perform visual inspection. Check to rule out some general failure factors.
 
The contents of the inspection include the following items:

(1) Check the air filter element and its surroundings for dirt, impurities or other 
contaminants and replace if necessary.

 (2) Check if the intake pipe is broken, leaking, aging or crushing.

 (3) Check whether the wiring harness of each sensor and computer is loose or 
disconnected, whether the wire is worn or short-circuited between wires, disconnected, 
whether the wire plug connector is inserted in place, and whether there is corrosion.

 (4) Check each sensor for obvious damage.

2、From simple and complex

Possible fault locations that can be inspected in a simple manner are checked first. For  
example, the intuitive diagnosis is the simplest. We can quickly find out some of the more 
obvious faults by using visual inspection methods such as watching, touching, and listening.

Intuitive diagnosis does not identify the fault, and when it is necessary to use the 
instrumentation or other special tools for diagnosis, it should also be checked first.

3、From known to unknown

Due to the complicated structure and working principle of the EFI system, the EFI systems of different models often have large differences. When checking and eliminating the faults 
of the EFI system, it is necessary to understand the working principle and structural 
characteristics of each EFI system. Detailed technical information of the model to be 
repaired.

4、Code Come First

  

As the EFI system becomes more and more complicated, it is more difficult to judge the 
fault location when a fault occurs. In order to facilitate maintenance, modern EFI 
motorcycles generally have fault self-diagnosis function.
 
When the EFI engine is running, after the fault self-diagnosis system detects the fault, it 
stores the fault in the memory of the computer in the code, and alerts the rider through 
the warning light.Therefore, during the overhaul, priority should be given to the fault 
diagnosis interface (socket) of the ECU, and the fault code in the ECU memory is called up 
by the manual jumper method or using the fault diagnostic tool according to a specific 
program, and the light flashes or Displayed directly in digital form by the diagnostic display, helping maintenance personnel quickly and correctly determine the type and extent of the 
fault.
 
After the fault indicated by the fault code is eliminated, if the engine fault phenomenon has not been eliminated, or if there is no fault code output at the beginning, then the possible 
fault location of the engine is checked.

After the troubleshooting, the fault code stored in the ECU memory is also cleared 
manually or manually by means of a specific program to record and store the new fault 
code.If the old fault code is not cleared, when the engine fails again, the ECU outputs the 
old and new fault codes together, so that the maintenance personnel do not know which 
faults are actually present in the engine, and which are faults that have been eliminated 
before, confusing the old and new fault codes. It brings difficulties to overhaul.

5、First Think Then Act

As everyone knows, chaos and bumps can only turn glitch into a big fault, and even cause 
irreparable conditions, causing undue losses. Therefore, it is necessary to first analyze the 
failure of the engine to understand the possible causes of the failure, and then perform the failure check. Only in this way can the blindness of the fault check be avoided: neither 
invalid inspection of the parts unrelated to the fault phenomenon can be performed, and the missing parts of the relevant parts can be avoided and the fault cannot be quickly 
eliminated.

6、First Back up then go ahead

Some components of the EFI system perform well or not. The electrical circuit is normal or not, and is often judged by parameters such as voltage or resistance. If there is no such 
data, the system's fault checking will be very difficult, and often only new parts 
replacement methods can be adopted. These methods sometimes cause maintenance costs to increase and time and labor.


Therefore, during the inspection, the relevant maintenance data of the vehicle should be 
prepared. In addition to collecting and repairing these inspection data from maintenance 
manuals and professional books, another effective way is to use the fault-free vehicle to 
measure the relevant parameters of the system and record it as a comparison parameter 
for the inspection of the same type of vehicle in the future. If you pay attention to doing 
this work, it will bring convenience to the fault detection of the EFI system.



Special Note: The failure of the EFI engine does not necessarily exist in the EFI system. If 
the engine is found to be faulty and the fault warning light is not lit (no fault code is displayed), in most cases, the fault may not be related to the EFI system. In this case, it should be like the engine is not equipped with the EFI system. The basic diagnostics are checked for 
faults.


Otherwise, you may encounter a fault that was not related to the EFI system, but it takes 
a lot of time to check the sensors, actuators and circuits of the EFI system, but the real 
fault is not found.