31st January 2004 (Forth Test)

This was the second test of the day and the engine was still warm from the previous test so the expected test period was expected to be short. The fuel tank was filled with 91 octane ESSO fuel. The engine was started and run for just under one minute. During this period the engine temperature would rise from 60 degrees Celsius to approximately 100 degrees Celsius at which point the engine was shut down. Data from the EIS and the oscilloscope were recorded along with a short video clip from a digital camera. The following charts indicate the performance for this second test run.

Engine & Propeller RPM

The following chart indicates the rpm as a function of time. The RPM was intentionally brought up slowly to ensure reliable data at the EIS. The chart still indicated a fluctuation in engine speed but the misfire and backfire was no longer evident.  The fluctuation was an accurate representation that was audible and recorded on the digital streaming camera. The engine did manage to achieve 4300 RPM but the erratic nature prior to 65 seconds indicated that the problem still existed.

Manifold Absolute Pressure (MAP)

As with the previous test for the day, the MAP was also recorded. At 25 inches of manifold pressure the engine reached about maximum RPM and further increase in MAP made little difference in engine output. This was quite disconcerting. At 60 seconds the MAP was reduced to 25 inches with little change in RPM but increasing the MAP to 30 inches at this point did give the a max RPM of 4300 which was also very stable.

Fuel Pressure

The gauge pressure for the fuel system was measured. Gauge pressure is the pressure above the ambient pressure. The fuel pressure regulator is supposed to regulate the pressure to be 34 p.s.i. above the manifold absolute pressure (MAP). The chart below indicates the fuel pressure as measured by the fuel pressure transducer located on the fuel rail just before the fuel pressure is regulated by the fuel pressure regulator.

The fuel pressure regulator is supposed to regulate the differential pressure to approximately 34 p.s.i. The following chart indicates the pressure difference across the fuel injector by comparing the manifold pressure to the fuel line pressure. There was also a correction to the fuel pressure reading to allow for the gauge correction of one atmosphere.

The fuel pressure was reading a little low and the though that the fuel pump may not be adequate crossed my mind.