Failure phenomenon

A 2012 Harley motorcycle (Figure 1) with a GP4 engine (V-twin).Cold engine stalls with rapid acceleration, but slow acceleration is normal.

2012 Harley-Davidson Motorcycle Exterior

Fault Diagnostics

In the absence of a dedicated fault detector.Unable to view engine data flowHowever, the mechanical structure and electronic control principle of the engine is similar to that of a car, so it was decided to use an oscilloscope to measure the relevant signal waveforms for analysis. Using the Macro Pico automotive oscilloscope to measure the relevant signal waveforms at the time of failure as shown in Figure 2, analysis shows that the engine immediately after starting the engine accelerated sharply, the engine stalled immediately.

Fig. 2: Correlation signal waveform during faults

Zooming in on the waveforms (Fig. 3) shows that the ignition signal and the fuel injection signal, when the engine speed decreases.However, the injection pulse width continues to increase (from 5.5 ms to 19 ms) until the engine stalls.The oil supply is thus suspected to be insufficient.

Fig. 3: Waveforms after amplification

Further Testing

Remove the fuel pump assembly and supply power to the fuel pump directly (Fig. 4), while measuring the fuel pressure and fuel pump current waveforms with a Honghong Pico automotive oscilloscope (Fig. 5).Fuel pressure found to be around 1.7 bar(1 bar=100 kPa), suspect fuel pressure is low. Check the service manual of this engine, and found that the standard fuel pressure is 380 kPa~425 kPa, thus confirming that the fuel pressure is too low, and deducing that the fuel pump is damaged.

Figure 4. Direct power supply to fuel pump

Figure 5. Fuel Pressure and Fuel Pump Current Waveforms

fault resolution

After replacing the fuel pump (Fig. 6), the engine accelerated sharply after cold start.Engine acceleration is normal.The problem was solved when the engine was no longer stalled.

Figure 6. Fuel Pump Replacement

Fault Summary

Motorcycles and car engines have similar mechanical mechanisms and electronic control principles, even without a dedicated fault detector to view the engine data flow, you can use the Acer Pico Automotive Oscilloscopes Capture the relevant signals and finally analyze the failure point.