Tuning Wiki

EDC15 fuel control and tuning basics

A practical introduction to EDC15 injection-quantity requests, limiters, injection hardware and related tuning concepts.

Updated by llandowtuninguk@gmail.com   Revision 2

Applies to
Bosch EDC15

Check the hardware and software limits stated in this article.

The short answer

Think of EDC15 primarily in terms of injection quantity (IQ): how much fuel is requested and how much the engine is allowed to receive. Bosch describes fuel-quantity control and limitation in its EDC15 examples, and says its torque-coordinated EDC architecture was introduced with EDC16. The Saab 9-3 D223L EDC15/VP44 documentation describes calculating a permitted quantity in milligrams per combustion and requesting that quantity and its timing from the pump.

This does not mean EDC15 ignores torque. Fuel quantity controls torque indirectly, and Bosch lists external torque intervention for EDC15V, EDC15M, EDC15P and its EDC15C common-rail overview. Actual signal representations, calculations and map arrangements vary with the vehicle and software; the following is a conceptual guide rather than a verified diagram of every calibration.

From pedal to fuel

  1. Read the request and conditions: The accelerator position and engine speed contribute to the requested output. Depending on the application, cruise control, idle control or another vehicle system can also affect the request. Sensors supply information such as air mass, boost pressure and temperatures.
  2. Select and limit quantity: The ECU determines a requested fuel quantity and applies relevant limits and corrections. Air availability, engine speed, temperature, starting conditions or an external intervention can affect what is permitted.
  3. Meter and time injection: The permitted quantity is translated into commands suited to the injection hardware, alongside a start-of-injection or start-of-delivery target. In Saab's VP44 example, the engine ECU sends the quantity and timing request to a separate pump controller.
  4. Control supporting systems: Depending on equipment, the ECU also controls boost and exhaust-gas recirculation (EGR), runs idle and smooth-running functions, manages starting aids and monitors faults.

These stages are simplified. A real ECU can calculate limits in parallel, use several corrections and switch strategies for starting, idle or faults. Do not assume a universal calculation order.

IQ, torque and units

IQ is often expressed as milligrams of fuel per cylinder per combustion cycle, commonly shown as mg/stroke. Some systems or definitions use a volume such as mm³/stroke, and some distinguish total cycle fuel from individual injection events. Check the signal definition, units and scaling: mass and volume are not interchangeable without a fuel-density conversion.

More fuel can produce more torque when sufficient air is available, but there is no single fixed conversion from IQ to Nm. Engine speed, combustion efficiency, air and injection timing affect the result. A map called a torque limiter can in some files limit an equivalent fuel quantity rather than contain values in Nm; inspect its axes, units and verified function. An external torque intervention or estimated torque signal does not by itself establish the architecture of the whole ECU.

Common requests and limits

  • Driver request: The pedal request and speed are used to determine desired output. A tuner may call the associated calibration the driver-wish map, but the exact maps and units must be verified for the file.
  • Torque or full-load limit: Restricts output to protect the engine and drivetrain or meet operating requirements. In a quantity-oriented strategy a fuel-quantity limit can also limit torque; its value is not automatically a measured torque figure.
  • Smoke or air limit: Restricts fuel according to available air and operating conditions to reduce excessive soot. Air mass is not the same thing as boost pressure, and sensor faults, leaks or turbo response can change which limit is active.
  • Other controls and corrections: Starting, idle speed, smooth running, maximum speed, temperature, atmospheric pressure, fault handling and external interventions can affect fuelling where fitted.

Raising one limit alone may not increase delivered fuel if a request or another limit is lower. Conversely, removing a restriction can increase smoke, heat or mechanical load and can hide a fault.

An illustrative example

Suppose a request corresponds to 48 mg/stroke, an applicable full-load limit allows 44 mg/stroke, and an air-related limit allows 38 mg/stroke. In a simplified lowest-value selection, the resulting quantity would be about 38 mg/stroke before other corrections. These numbers are invented; real applications may combine limits differently and do not all use this exact sequence.

Injection hardware changes the details

  • EDC15V, distributor pump: Bosch shows a port-and-helix-controlled distributor pump with a quantity actuator and timing-device valve. Pump metering and timing feedback are part of the system.
  • EDC15M, distributor pump: Bosch shows VP30/VP44 solenoid-controlled pumps. In the Saab VP44 example a separate pump control module receives the requested fuel quantity and timing; arrangements depend on the installation.
  • EDC15P, unit injectors: Bosch shows individually controlled unit injectors and calculation of start of delivery and delivery period. A mechanically driven unit injector is not a common-rail injector.
  • EDC15C, common rail: Bosch shows a common-rail EDC15C/MS 6.3 system with rail-pressure control and electrically controlled injectors. Rail-pressure targets and feedback are relevant to this hardware; a distributor-pump or unit-injector application does not have the same common rail.

The suffix and ECU label are useful clues, not a substitute for identifying the actual fuel system and exact software. Do not carry map addresses, units, pressure settings or injector assumptions from one variant to another.

Timing, air and other functions

Injection timing and delivery duration affect combustion, performance, noise, emissions and component loading. Bosch describes start-of-injection targets that depend on speed and fuel quantity, with corrections for conditions such as temperature. The means of achieving and checking timing differ between pump, unit-injector and common-rail systems.

Where fitted, boost control regulates the air system and EGR control affects the fresh-air charge. Starting quantity, glow control, idle control, cylinder balance, cruise control, immobiliser and diagnostics are among the functions Bosch lists for EDC systems, with equipment and availability varying by application.

A practical starting point

  1. Record the vehicle, engine, fuel system, ECU hardware number and complete software and calibration identifiers. Keep a recoverable original read and establish a healthy baseline.
  2. Match the definition to that exact software. Record the axes, units, scaling and evidence for each request, limiter and timing map; a familiar label alone is not proof.
  3. Understand the request, quantity limits, measured air, boost control, injection timing and hardware together. On common-rail systems include requested and actual rail pressure where available.
  4. Where the diagnostics expose them, compare requested and limited fuel quantities, air mass, requested and actual boost, temperatures and relevant faults during controlled testing. Diagnose unexpected limits before adjusting calibrations; verify changes against the actual engine and injection system.

Starting, idle and cylinder balance

Bosch’s general EDC description uses a separate starting quantity based on coolant temperature and cranking speed; its example does not use the accelerator request to set that quantity during starting. Once running, idle control adjusts fuel to maintain the desired speed as temperature and auxiliary loads change. These are documented control principles, not proof that every EDC15 file uses the same switching conditions or maps. Bosch, printed pages 50–52.

Where fitted, smooth-running control compares crankshaft-speed changes associated with individual cylinders and adjusts their fuel quantities to reduce differences. A displayed correction reflects the control system’s response and does not identify the fault by itself. Bosch also describes active surge damping and maximum-speed control for its general EDC examples. Bosch, printed pages 50–53.

For the physical metering and timing methods behind the different fuel systems, including the 2001 Saab 9-3 D223L VP44 example, see EDC15 injection systems and timing feedback. For examples of driver, smoke, torque and other diagnostic quantities, see EDC15 diagnostic data and troubleshooting.

Volkswagen’s SSP 304 describes the later EDC16 V10 TDI coordinating torque demands and then calculating and limiting the necessary fuel quantity. It is useful for comparison, but its V10 unit-injector details should not be attributed automatically to an EDC15. Volkswagen SSP 304, printed pages 4 and 8–10.

Sources

Curated reference notes. Applicability follows the cited sources; hardware testing by this wiki is not implied.