Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Fuel injection, basic function
- Basic calculation of fuel mass/combustionÂ
The current air mass/combustion is divided by 14.7 and moved to section 2. The unit is now mg fuel/combustion.
- CompensationÂ
In cases of cold engine, short time after start, fast load changes, knocking or high load, the current value is multiplied by a compensation factor.
- Lambda controlÂ
The lambda control value is multiplied in. The value is moved to section 4.
- Correction for purgeÂ
Multiply by the value for purge adaptation. The value is moved to section 5.
- Multiplicative adaptationÂ
The value from the multiplicative adaptation is multiplied in and the new value moved to section 6.
- Additative adaptationÂ
The value from the additative adaptation is multiplied in and the new value moved to section 7.
- Start fuel massÂ
If the engine has not yet started, the start fuel mass is determined.
- Fuel mass/combustionÂ
The fuel mass/combustion is the mass of petrol to be added to the engine on each combustion.
- Injector opening timeÂ
Converts the fuel mass to injector opening time in ms.
- On injection twice/combustionÂ
Before the engine is synchronized, i.e. the camshaft position found by means of the ignition system, injection occurs twice per combustion. The injection time calculated in block 12 is divided by two.
- Needle lift compensationÂ
The voltage-dependent needle lift time is added to the injection time. This compensates for the delay between activation of the current in the injector coil and supply of the fuel.
- Fuel shut-offÂ
Under certain conditions, e.g. on engine braking, car immobilized, the fuel shut-off can apply. The injection time is then zero.
- Selection of fuel shut-off functionÂ
- Activation of injectorÂ
The ECM controls the injector which is currently supplying fuel, and the sequence is controlled by the ignition sequence. The camshaft angle at which injection takes place depends on the prevailing operating conditions.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.