Aftermarket April 2022

BY Frank Massey I left off last month with a road map and a suggested list of diagnostic options, with several serial errors, some of which were predictable given the mix. It is easy to be drawn into a quick fix based on experience, so I intend to explain in detail just how complex this drivetrain is and hopefully illustrate how we should be reacting to our waypoints. Are fault codes clear enough? Can we trust them? More importantly, what caused them? We should always approach faults in a progressive logical order; However, this is often modified due to accessibility restraints and cost. For example, conduct the quick and easy tests first, while the engine runs. Once disassembly starts our test options are limited. One misfire count per 1,000 RPM: Direct or coil on-plug ignition is easy to evaluate providing you use an oscilloscope. Each coil has three circuits, an independent 5- volt square trigger from the PCM and the thin cable. Power and ground circuits are shared across all the coils. Current flow is an internal function of the coil assembly, however dwell or saturation and ignition point is controlled via the 5-volt PCM trigger. Please refer to Fig.1. This shows a Pico screenshot illustrating normal function, spark burn time 2.5 m/s and peak current flow of 15 amps. The slope (burn line angle) suggests a clean plug with normal physical loads. The secondary image was achieved by an inductive probe. Current flow via power or ground is achieved by an inductive Hall probe. Our vehicle displayed good patterns across all coils. However, the expression misfire can be accredited to ignition, fuelling or mechanical faults. We have yet to establish the validity of the cam crank position error codes. The map sensor value error cannot be addressed, as a valve timing error would directly cause manifold pressure deviation. 30 AFTERMARKET APRIL 2022 TECHNICAL www.aftermarketonline.net PART TWO PROCESS NOT PROBLEM Frank’s ongoing look at the recalcitrant VW Golf R serves as an example of why process will win every time The next interesting feature of the 888 engine is the dual injection system. Cranking from cold, the high-pressure injectors operate with three delivery events. Once running and below 45°, high pressure fuel is injected over two delivery events at 60-80bar for approximately two minutes. The port injectors now take over fuel delivery at 4-6 bar pressure via the J538 pump control module. A word of advice; This is subject to adaptive control. Port injection then provides fuelling across all the low mid load ranges therefor it seemed reasonable to evaluate the port injectors next. All port injectors were evaluated in our ASNU test bench. As the high-pressure injectors required considerable disassembly, our next test focus was the camshaft- crankshaft synchronisation. It is helpful to explain how the valve timing is adjusted across the operating range. From cold, with the high lift exhaust cam operating, and 30° advance angle, the inlet timing is set to 0°. Above 45°, the low lift exhaust cam is triggered, retarding the cam to 0-4° advance angle. The inlet now adopts 15° Fig 1.