The purpose of this test is to evaluate crankcase pressures during cranking conditions using the WPS500X pressure transducer.
This known good waveform has the following characteristics:
Combustion gases escape past the piston rings and into the crankcase during an internal combustion engine’s operating cycle. This effect is known as blow-by.
A crankcase ventilation system is used to vent blow-by gases back to the intake manifold, whilst fresh air is drawn in to replace them. This has two effects:
Fresh air enters the crankcase via a breather, which has its inlet close to and downstream of the air filter. A Positive Crankcase Ventilation (PCV) valve regulates the flow of blow-by gases from the crankcase to the intake manifold.
The PCV valve is a normally closed valve. That is, when the engine is off and the crankcase and intake manifold pressures have equalised (with atmospheric pressure), the valve is fully closed. This prevents harmful gases from venting to the atmosphere when the engine if off and the vehicle is stationary.
The higher the crankcase pressure above the intake manifold pressure, the greater the opening of the PCV valve. Therefore, the valve position and gas flow vary with engine operation, as follows:
The measurement of crankcase pressure, usually by connecting at the dipstick tube, breather inlet, or other convenient access point, allows us to assess the degree of blow-by and the operation of the ventilation system.
The crankcase pressure waveform features have the following relationship with engine operation during cranking:
Diagnoses rely mostly on the identification of periodic anomalies within the waveform. An observed anomaly provides sufficient justification for further investigation.
Periodic waveform anomalies will occur if there is:
An overall low crankcase pressure will occur if:
An overall high crankcase pressure will occur if:
A faulty PCV valve or system can affect an engine’s fuel trims and cause either lean or rich running conditions (depending on the fault). In these cases, the engine management system may switch on the MIL light and set a diagnostic trouble code (DTC).
Other related symptoms may include erratic idle/running, oil burning/blue smoke, or the contamination and build-up of carbon, water, or sludge, within the crankcase, breather, PCV valve, and connected systems.
We know that our PicoScope users are clever and creative and we’d love to receive your ideas for improvement on this test. Click the Add comment button to leave your feedback.