My father-in-law is a retired nurse, so I sympathize if this is your first dive into engine mechanics. I’d be quite lost if I was asked to troubleshoot a kidney or describe why we have a pancreas. I don’t mean to discourage you at all, but can confirm that there is a vast body of knowledge underpinning modern vehicles and you will first need a framework to drop the facts and concepts into. If you can share how well formed your personal framework is then we can better tailor our replies to your current level. [Edit: this post overlapped with Bill’s, so I aimed perhaps a little low...
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My technical background is an eclectic mix of square-rigged sailing, mechanical engineering, ship building, yacht maintenance, and even software systems design and programming. (I can be INSTANTLY boring at dinner parties in several fields!) And I appreciate that I have come to the Sprinter with a body of theoretical knowledge that makes it easier for me to navigate the interplay of its systems, but I still try to be selective in what I will dive into and what I simply treat as a black box where magic happens.
Diesel control has come a LONG way since I started learning about them, but they still boil down to “inhale-sqeeze-spray-exhaust”. Fuel injectors can use individual cam-driven mechanical pumps to push a metered volume of fuel into the cylinder, but with CDI engines the injectors are instead electronically controlled valves that pop open and closed with wondrous precision to release fuel from the common high-pressure rail into the cylinders. This makes the ignition timing, fuel quantity, and fuel flow rate things that can be precisely varied by the control system. This is beyond complex, so I take it on faith that the engineers got it right (black-box approach), but at the same time I am aware that there are inputs required for the black box ECU to make these decisions, and other valves and controls required to make the desired adjustments. The manifold air pressure controls the amount of oxygen entering the cylinder, so we have a turbo vane control and a MAP sensor. Lean combustion with an excess of O2 leads to NOx production and high exhaust temperature, but diesels don’t have a throttle plate valve to limit incoming air so we have an Exhaust Gas Recirculation system to instead displace some of it. The fuel rail pressure and opening timing of the injectors controls the amount of fuel, so we have a rail pressure sensor and a pressure relief solenoid. The high-pressure fuel pump has a quantity control valve to limit pumped volume and avoid overwhelming the relief solenoid. Glow plugs help light the fire during engine warmup, and the O2 sensor in the exhaust pipe tells the ECU how the combustion turned out. The Mass Air Flow sensor gives inputs on how much new air is coming in, and is used to help set the fuel quantity for clean combustion, and the Cam- and Crank- position sensors allow the ECU to time the opening of the injectors. At high RPM the fuel has less time to be injected before the piston has moved down the cylinder, so the rail pressure is increased to spray the fuel out faster. At lower speeds rail pressure is lowered again. Temperature sensors keep an eye on ambient conditions, and oil and cooling systems keep the engine from self destructing. The chemistry of these fluids breaks down with use, so they are changed periodically, with some intervals based on time (the G-05 coolant) and others on use (engine oil)
Again, the fluid technology has advanced with time, and today’s fluids *can* be very stable, but the chemicals that make them stable can also create problems for other components. For example, the additives that make engine oil stable can clog the exhaust filters fitted on the newest engines (not an issue for T1N’s DPF-free exhaust system) and the wrong coolant can damage the gaskets and seals inside the engine (as GM has recently demonstrated, with weak coolant resulting in blown head gaskets)
Okay... bit of a brain dump, and perhaps another audience I won’t be dining out with, but hopefully useful to shine some light into what all the solenoids and sensors on our engines are doing during operation, and how their malfunction can affect them.
-dave
