When the fuel arrives changes the same quantity
Bosch states that the start of injection has a critical effect on power, fuel consumption, noise and emissions. The desired value depends on engine speed and injected fuel quantity, and it is stored in maps. Coolant temperature and ambient pressure can adapt it. The same milligrams per stroke therefore do not produce the same torque, the same noise or the same smoke if the timing moves. Bosch, start-of-injection control.
How that timing is checked depends on the hardware. In-line and some distributor pumps can close a loop on a nozzle needle-motion sensor, but only while fuel is actually being injected and speed is stable. During starting and overrun the sensor is not described as usable, so the loop cannot close. Solenoid-valve distributor pumps such as the VP30 and VP44 can control the start of delivery from a pump angle signal even during overrun, so the timing device can be waiting at the right place for the next injection. Common rail, in this 2001 description, does not need that needle-motion loop: injector triggering itself is treated as repeatable enough. Later common-rail engines are not all this system. Confirm the hardware before transferring any of these loops. The EDC15 hardware split is in EDC15 injection systems and timing feedback.
Pilot injection and combustion noise
A single main injection is what Bosch associates with torque. On common rail, injection pressure is separate from the moment and the duration of injection, so other events can be added at the same pressure. Pilot injections are described with the principal objective of reducing combustion noise. Post injections are described as serving exhaust emissions, and they are small quantities. The injected quantity of an event is the product of injection pressure and the time the injector is open. Bosch, solenoid-valve-controlled injection, common-rail triggering.
Noise, smoke and torque are therefore three results of one combustion, not three independent maps. A pilot that is late, early, too large or missing changes the knock the driver hears and can change how much of the main quantity burns cleanly. A rail-pressure change scales the quantity that a given opening time delivers, and it changes the atomisation the combustion noise depends on. Bosch's rail-pressure loop compares the sensor with the desired pressure and drives the control valve; at high speed and low fuel demand, some pumps can switch a pumping element off to reduce strain. A clatter that appears only at light load, or a quantity error that appears only when pressure is high, belongs in this loop before it belongs in the driver's wish map.
Unit injectors are not this rail. A mechanically driven unit injector does not have a separately regulated common-rail pressure. EDC16's V10 and V6 examples are contrasted for that reason in EDC16 torque and fuel.
What the driver feels
- Diesel knock when cold is timing, pilot and glow together. Post-glow is described as reducing cold combustion noise as well as misfire and smoke. See cold start and warm-up.
- Knock that appears as the pedal opens, then fades can be the pilot schedule leaving the region it was calibrated for, or rail pressure not yet at the new target. Log desired and actual pressure through the transient.
- A power change with little pedal change can be timing. Torque-controlled EDC still needs the correct injection point, not only the correct quantity, before the estimated torque is real. Bosch, torque control and the injection point.
Advancing or retarding a start-of-injection map to chase one of those symptoms also moves emissions and component temperature. This page does not give a timing offset. Match the map to the injection system and judge it from noise, smoke, torque and temperatures together.
Petrol is a different timing
Spark advance is the petrol equivalent only in the sense that it moves combustion relative to the piston. It is not a diesel start-of-injection map, and it is limited by knock. That subject is ignition timing for performance and, for ME7, ME7 ignition and knock. Direct-injection petrol can have its own injection events, documented per engine on the MG1 and Simos pages, and those events are not diesel pilots.
Sources
- Bosch Electronic Diesel Control (EDC), 2001, independent PDF mirror. Start-of-injection control, common-rail pilot and post injection, rail-pressure control, and the role of injection point in torque control. Printed pages 52–54, the solenoid-valve injection chapter from page 66, and pages 75–77. Accessed 2026-11-11.
- EDC15 injection systems and timing feedback. Hardware differences behind the timing loop.