Symptoms

Insufficient power or gradual loss of power, jerks when accelerating, the maximum speed cannot be reached.

Cause – erroneous signals from the air flow meter

Oil mist in the intake air, fumes from silicone gaskets, etc.. they gradually settle on the surface of the sensor resistance diaphragm in the mass air flow meter. Due to the contamination of the diaphragm, the signals sent by the air flow meter to the controller are subject to increasing errors. This slow process is often unnoticeable by the self-diagnosis system and usually there is no record of it in the fault memory..

The final heating phase of flowmeters existing at some manufacturers was designed as a way to clean the resistive diaphragm by the so-called. Burn clean with engine shutdown. In practice, however, quite the opposite often happens. Firing promotes "baking" of the contaminants. They are formally vitrified at the sensor surface! This sometimes leads to incorrect information being sent to the EDC.

Troubleshooting and fault elimination

Due to this, that the changes are slow, Often no fault is stored in the fault memory, and if anything, these are at most as "implausible signals" of the air flow meter. The flow meter can be checked with an appropriate diagnoscope and current factory values, comparing the mass of the air actually sucked in under load with the required value. In practice, however, it turns out, that even new flow meters, fitted as a spare part, checked and considered good, but working very close to the lower tolerance zone, are responsible for insufficient engine power, often in well-defined speed ranges or certain load ranges. In such a case, the oscilloscope can provide the necessary information to evaluate the operation of the flowmeter. The auxiliary cable leads the voltage signal from the flowmeter to the oscilloscope. Then, a strong acceleration from the idle speed simulates the engine load and compares the image from the oscilloscope with the image required. If the flow meter is defective, the signal waveform will appear jagged, with distinct bends in several places, indicating the ranges, in which the client feels jerks. However, the maximum speed is not reached then, when the output signal to the controller is generally too low. In individual cases, when symptoms keep repeating, the advisability of immediate elimination of the final heating phase should be considered, i.e.. Burning clean sensor surface after stopping.