Oilyma

Fuel trims in a BMW

NB: You can’t exactly add the Lambda Control to Additive or Multiplicative because mathematically it won’t add up exactly.

NB: Global OBDII fuel trim values won’t react the same way as other non-European cars.

Adaptation Values Explained

Additive is LTFT at idle
Multiplicative is a LTFT at part load
Lambda Control is STFT

Multiplicative mixture Adaptation (higher rpm)

A healthy engine has virtually a value of 0.00 in multiplicative adaptations.

greater than 8% = lean
less than -8% = rich
The negative multiplicative fuel trim reading of -4.51% means it is rich and subtracting fuel at part throttle.

Additive Mixture Adaptation (idle, lower rpm)

Measurements: ms or mg/stroke

greater than 0.2ms = LEAN, adding fuel
less than -0.2ms = RICH, subtracting fuel
The .68 mg/stroke means it is adding fuel at idle.

--	LTFT Negative (-)	Source
1	Not enough air is reaching the combustion chambers.	Damaged catalytic converter that causes high exhaust back pressure. At idle this can drive fuel trims in opposite directions, producing a positive STFT and negative LTFT. You can see signs of high exhaust back pressure on a scan tool; calculated load will be low at wide-open throttle (WOT) and fuel trims will trend negative as engine speed increases.
2	More than the commanded amount of fuel is reaching the combustion chambers.	Leaking injector
3	One or more sensors is reporting incorrectly.	MAF / O2 Bank 1 / O2 Bank 2

--	LTFT Positive (+)	Source
1	Unmeasured air is reaching the combustion chambers.	- Post-MAF vacuum leak - High fuel trims at idle are a classic symptom of a vacuum leak, especially if LTFT decreases at higher engine speeds"
2	One or more sensors is reporting incorrectly.	MAF / O2 Bank 1 / O2 Bank 2
3	Less than the commanded amount of fuel is reaching the combustion chambers. (Low fuel delivery)	Clogged Injectors / Weak Fuel Pump / Clogged Fuel filter / clogged fuel lines

Mixture Adaptations of a N52b25 with an internal vacuum leak

The screenshot shows that the PCM -in both banks- is adding lots of fuel at idle and very low throttle but substracting it at higher RPM.

This is because the higher the engine RPM , the less impact an internal vacuum leak has on performance and fuel effeciency.

Bank 2 is the most impacted (0.81 mg per stroke). Theoritically the DME tries its best in keeping the engine balanced, which means in this case that Bank 2 is driving Bank 1

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Automatic test for detection of carbon deposits in the intake ports in the test module for misfire

Depending on the driving profile and/or fuel quality, deposits may form in the intake ports and on the intake valves. These deposits can over time lead to driving complaints and fault code entries in the Digital Engine Electronics (DME). The following symptoms may occur during vehicle operation:

Rough idle

Brief jerking/surge and or combustion miss in the engine-speed range between 2000 and 4000 rpm during full-throttle acceleration
The test for carbon deposits helps determine whether deposits that can affect engine performance are present in the intake ports.

Test procedure

A "sooted" engine will have greater valve overlap combined with problems with residual gases, and as a result it will run more roughly than a "clean" engine. This can be measured using rough running values that indicate combustion consistency within the engine.

Switch off all electrical equipment and always connect a battery charger in order to minimize the load on the engine.
Engine temperature should be below 45 °C, as the effects of carbon deposits are more difficult to detect when the engine is warm. Steps should also be taken to prevent the electric fan from starting during the test
The timing of the exhaust valve is locked in, while the intake valve's timing is continuously adjusted from advanced to retarded in order to cover a range extending from maximum to minimum valve overlap.
The rough running values indicating combustion consistency are simultaneously recorded for subsequent evaluation.
The result that is then issued indicates whether it will be necessary to clean the intake ports.