February 2021

FEBRUARY 2021 AFTERMARKET 23 Fig 2: High pressure pump priming system by David G and the issues with high- pressure control during cold start and warm up strategies. Low pressure was confirmed normal at 4.5 bar with no cavitation. At this point, I need to explain how the EN888 engine utilises the dual injection system. From cold and during the warm-up phase, it employs only the high-pressure injectors at approximately 60 bar pressure, with three injection events during crank start. This is reduced to two injection events per cycle until the low-pressure manifold injectors take over. More about camshaft timing later – it’s going to get quite complicated. Once started it continues with high pressure injectors for the entire warm-up period with two injection events in what “I” call homogenous and stratified delivery. Let me explain. Two thirds of the fuel required is on the intake cycle, homogenous mixture, with the final event on compression stroke, stratified delivery. It then switches over to manifold injection at low- pressure, approximately 5 bar for the entire low to mid- range load strategies. The high-pressure system is only used for high load and engine RPM strategies. The reason for this is quite revealing! Direct injection strategies can produce higher particulates and NOx emission levels than diesel during lean fuelling and high load strategies. Now, I’ve been a bit in the back-seat so far, what will all the sheer number of cooks in the car, looking to find the kitchen. Part two is where I take a more direct involvement in assessing the previous tests using the Pico scope and cross-referencing serial values and pcm correction. I promise some remarkably interesting results. Join us next issue for the continuation. In the meantime consider how you think the PCM should respond to sensor input, fuel trim, injector period and high rail pressure.