8th February 2004

Since the last test conducted on 31st January an additional fuel pump (Subaru submersible type) had been added and the fuel octane rating had been increased from ESSO 91 octane to Sunoco 94 octane. The original fuel pump was one that I had bought some time ago as one that could be run outside of the fuel tank unlike the Subaru model which operated submerged within the fuel. The electrical current flowing through the original pump measured at 3 Amps whereas the current flowing through the Subaru submerged pump was 7 Amps. At this point I was convinced that the problems of engine instability revolved around fuel starvation with a possible contribution from the knock sensor causing the ignition to retard at high power when using the ESSO 91 octane fuel (The compression ratio for this engine is 10:1).

During the course of the week some tests had been conducted at increased power levels. These tests measured the following parameters:

• Ignition timing
• Ignition dwell period
• Fuel injector timing
• Fuel Injector open period

These tests were conducted by connecting a digital storage oscilloscope to four sensor lines:

• Channel 1        Cam angle sensor
• Channel 2        Cylinder #5 ignition coil
• Channel 3        Cylinder #5 fuel injector
• Channel 4        Crank angle sensor

The engine was then started and the RPM increased to a set value. At that set value the oscilloscope was triggered and the engine switched off almost immediately afterwards. The signal data found on the oscilloscope was measured and recorded along with the data captured from the EIS monitored on the PC. The test was repeated at the next power setting. At the higher power settings MAP was increased rather than the RPM since the engine speed was so erratic at the high MAP values. The picture below shows a photograph of the traces seen on the oscilloscope.

Engine & Propeller RPM

With high octane fuel and added fuel pressure capability I expected this test rum to be successful. The tach plots  below indicated to the contrary.

Manifold Absolute Pressure (MAP)

The MAP is indicated in the chart below. The characteristic start cycle is evident