The reading bellow illustrates current content of ambient air. This content will be a starting point for the emission analysis. The machine will examine the proportion of gases measured either in ppm (parts per million) or % ( percentage).
After the engine was started and was running cold we memorised this data:
The concentration of two gases such as carbon monoxide (CO) and hydrocarbon (HC) indicates that the air/fuel mixture is quite rich immediately after cold start. Not all CO molecules can combine with oxygen and fuel (hydrocarbons) is not burnt completely. Other figures are just normal for this stage of engine running.
CO has fallen dramatically. This means that mixture is not so rich anymore. Lambda tell us that fuel mixture is just slightly rich. CO2 and O2 are normal. But look at hydrocarbon. 253 ppm is relatively high for this car been warmed up. To my understanding of what is going on here are some problems with ignition. Fuel could be burnt a bit more efficiently. Putting in account that lambda is 5 % richer than stoichiometry and proper figures for CO2 and O2 I suspect ignition system, probably just spark plugs.
As it is seen on the screen at 2500 RPM carbon monoxide increased in 16 times compared to the idle RPM. At the same time there are no changes in hydrocarbon and slight changes in O2 and CO2. It's reasonable because the air fuel mixture is richer at higher RPM.
Experimented with MAP sensor we simulate the situation when engine runs very rich. Have a look at the figures below:
All the sudden acceleration always means instantaneous fuel injection and rich mixture in the combustion chamber:
Simple experiment with unplugged spark plug allows watching unburned fuel which is represented in high volume of hydrocarbon:
With disconnected injector we have lack of fuel. This imbalance was read by the machine immediately:
The last experiment we did was turned on the air conditioning system:
The engine runs slightly lean with a small load on it by air conditioning compressor. CO2 and O2 are normal. But after all our experiments HC is 25 ppm. It looks like the engine was not warm enough in the beginning of the experiment.
All these tests above lighted up the key points of the modern engine management system. The evolution of engine performance and efficiency from the economical point of view are based on the principle of continuous reading signals from sensors and feedback to the ECU while it is in closed loop mode. Moreover, this is the way how the emission can be reduced considerably what is the major for responsible manufacturer. To get this system working the oxysensors were employed. The faster these sensors come to the operation temperature the less emission we’ll have. That’s why O2 sensors differ in their wiring. 1-wire type is the old one with signal wire and grounding through the body. 2-wire type has signal wire and separate earth wire. 3-wire has signal wire, ground wire, and heating element wire. The heating element is used to reduce time to reach operating temperature and lower emission. 4-wire oxysensor has supply voltage wire and ground for heating element, and also ground for signal wire. All of these mentioned sensors are switching type or they also refer to as HEGO ( heated exhaust gases oxygen sensors).
But 5-wire O2 sensor is wide-band sensor. The wires in this instance are heater voltage supply and ground, reference ground for both senceing cell and pumping cell, signal from the sencing cell to the ECU, and current wire for the pumping cell. The construction of this type wide range air fuel sensors can differ and so far numbers of wires can be higher. The invention of WRAF sensors allows to control how lean and how rich is the mixture. Thus, this sensor is not switching type device. It provides more precise data for the ECU.
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