Engine management: Past and future

Dealing with engine management systems has come a long way since the 1970s. Frank looks at where things were and where they are going

Published:  06 June, 2019

I have long accepted that nothing stands still for long in this industry. Just when you think you have a grasp of the subject something is sure to upset it. Nothing illustrates this more than powertrain diagnostics. Initially this was called fuel injection, and later became engine management. Now I’m afraid it’s even more complex.
I find myself fortunate to have been there at the beginning; Bosch l Jetronic, a 25 pin ECU with if I recall correctly, only 13 pins occupied. No serial diagnostics, no specific tools. So why was I fortunate? Consider my reflection on diagnostics back in the late 1970s and see if they are still applicable today.

Firstly, you had to understand what the system had to achieve, what components it had at its disposal, what role they played and how they interacted within that system.

The next challenge was measurement values; what to expect under a variety of conditions, and what equipment was required to access this information. This all seems so straightforward now, but in those days it was a little like Columbus sailing across the ocean. He knew it was wet, he needed a boat, he knew which way west was, despite this being blasphemy in the eyes of the Pope, and so set off without a clue as to what was out there.

Hardly a logical diagnostic process, however I was writing the rule book and did understand the meaning of the words test don’t guess. So, what’s changed that undermines these basic principles?

Acessibility
With even the most basic of vehicles now relying on a level of technology that makes accessibility almost impossible, OE manufacturers totally forbid any intrusion within the wiring loom and I am sure this explains the why design and manufacture precludes access as a high priority. However, we are brave, and have the Starship Enterprise at our disposal for our journey of discovery.
The problem is one of integration. Systems don’t function in isolation any more, and Columbus now has to map the Americas and Australia at the same time. In order to conduct an accurate assessment of a function it must be in its natural environment and be observed when functioning normally.

Complexity
This is not restricted to a physical state. It also includes software, algorithms, and predictive response, correction or adaptive action. Systems now change their mode of operation based on environmental influences, affected by a very wide range of changing influences. Cylinder select or dynamic stability comes to mind. The driver selects an option from a long list of choices, engine, transmission, and chassis. I used to say that for a function to occur it must have a command followed by response. In today’s world,  the command may be a software decision followed by a constantly changing response, stratified and homogenous fuelling, infinitely changing camshaft timing and variable valve lift to name a few.

Test options
Manufacturers are driven by non-intrusive process dictated by guided diagnostics. Pre-determined test plans more often or not end with a pass or fail result, foregoing any data reveal.  Is this due to a control of process and cost, or a mistrust in their techs? Actual evaluation of circuits, voltage, current or complex profile is getting ever more difficult. Attachment of gauges in order to measure pressure and flow is often restricted by sealed transit hoses or internal ducting within castings. Serial data has become so much, more powerful and trustworthy, however it does not and will not replace the functions available from an oscilloscope. Specialist mechanical tools and assembly techniques prohibit casual examination, due to cost or the ever more common single fitment parts.

Data extraction
This may lie in a multitude of directions; Physical extraction, camshaft timing, fuel quantity per stroke via the serial port or fuel pressure rise time via the scope. We are forced to monitor not just a physical value, but not how the PCM is adjusting or adapting a value. How do we know the parameters of operation when VMs are removing more and more data in favour of the pass-fail flags from a software automated test profile?

SENT
Rieve gauche, no not a walk along the Left Bank, but a completely new protocol for data and diagnostic transmission. SENT has been developed specifically for automotive applications, rather than being a black-market hooky copy from other engineering developments. SENT stands for single edge nibble transmission, and is a uni-directional out-only data line to the PCM. SENT is essentially a serial interface, used predominantly with throttle position, air mass and temperatures. The basic unit of time is the tick, with a minimum data unit nibble. 0Data transmission speeds over fast or slow channels, where bitrate can also vary: 1xtick= 3us. In essence it is very similar to a single channel can transmission, where the function includes synchronisation, calibration, CRC and checksum.
How am I to challenge the authenticity of data? For example, sensor error may come from power or ground discrepancies, range error, environment influences, calibration error or simply a genuine condition fault. Its design is of course intended to provide an autonomous diagnostic platform via the serial port, excluding any assessment by the techs.

Full circle
What does this mean for the industry? I suspect it will go full circle back to the 1970s, when part swapping was the norm for Christopher Columbus frauds.

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