Contents: The lambda probe measures the amount… ↳ Catalytic converter operating… ↳ Handling the catalytic converter ↳
Fuel mainly consists of carbon and hydrogen. When burned in an engine, carbon combines with atmospheric oxygen to form carbon dioxide (CO₂), hydrogen (H), combining with oxygen (O2), forms water (H2O). About 0.9 liters of water are formed from 1 liter of fuel. It is imperceptibly removed through the exhaust system in the form of steam. In winter, after starting a cold engine, you can often see white clouds of exhaust - this is a sign of water condensation.
Focus with triple-acting catalytic converter - diesel engine with oxidation catalytic converter and exhaust gas recirculation.
All petrol Focus models in Germany are equipped with a triple-acting catalytic converter: both diesel variants have an oxidation catalytic converter and an exhaust gas recirculation system, which reduces the concentration of nitrogen oxides in the exhaust gases. When operating, the regulated catalytic converter reduces the proportion of carbon monoxide by about 85%, hydrocarbons by 80% and the proportion of nitrogen oxides by about 70%. Oxidation catalytic converters allow nitrogen oxides to pass through, which is why diesel engines have recirculation. The designation "regulated" indicates that the exhaust emissions, unlike the oxidation catalytic converter, are actively measured in operating mode (lambda probe) and adjusted to the range of the statutory minimum. As the mileage increases, each catalytic converter loses its effectiveness.
"Hot spot": the lambda probe in Zetec-SE engines is located directly in the exhaust manifold under the heat shield
The lambda probe measures the amount of oxygen in the exhaust gases
The Focus's lambda probe is located directly in the exhaust manifold. To reduce the "poison sniffer's" reaction time, it is additionally heated electrically. Lambda probes constantly analyze the proportion of residual oxygen in the exhaust gases. The information obtained serves as the basic parameters for the electronic engine management: depending on the measured values, the on-board computer determines the composition of the air-fuel mixture (rich, lean). This is done in a rapidly changing sequence: excess air for combustion of hydrocarbons, insufficient air to reduce nitrogen oxides. The regulated exhaust gases pass through a catalytic converter, which, as described above, converts them into carbon dioxide, water vapor and nitrogen.
Catalytic converter operating temperatures
In order for the catalytic converter and the lambda probe to function, they must first be heated to operating temperature (the catalytic converter up to 300°C). The exhaust gases do this within 25-80 seconds. But both units react extremely sensitively to excessive heating. For example, if unburned products of the fuel-air mixture ignite in a hot catalytic converter (during ignition interruptions), the temperatures inside can rise to dangerous levels. At a temperature of about 1200°C, the catalytic converter ages prematurely, at 1400°C the ceramic body melts, and the lambda probe also overheats. A melted catalytic converter gives itself away with a hissing noise from the exhaust, caused by the back pressure of the exhaust gases - and a loss of engine power. Find out the cause carefully, otherwise the new catalytic converter will not last long and the exhaust valves of your Focus will also burn out in a short time.
Keep an eye out for misfiring in your Focus, especially when downshifting or when driving downhill in idle mode: if there's a clicking sound in the exhaust system, find out the cause.
Oxidation process in the catalyst (diagram). The catalytic converter consists of a cellular body of a ceramic support 1, which rests in an elastic, vibration-damping metal fabric 2. This package is surrounded by a heat-resistant housing made of high-quality steel 3. In order for the incoming exhaust gases to flow evenly through the cells of the catalyst, a sieve 4 is located in front of it in the form of a funnel
Handling the catalytic converter
If your Focus won't start because the battery is dead, avoid pushing or towing. This can introduce too much unburned fuel into the catalytic converter, which will cause it to fail for a long time.
Misfiring indicates a problem with the ignition system. Determine the cause of the symptoms as soon as possible or have a specialist do it.
Before applying a fresh anti-corrosion coating, "pack" the catalyst well, otherwise there will be an acute risk of fire later.
If necessary, also check the heat shield above the catalytic converter for damage.
A leaky exhaust system (burnt gasket, thermal cracks, corrosion damage, etc.) before the lambda probe distorts the measurement values (increased oxygen content). As a result, the electronic engine control enriches the mixture. You will pay for the electronics' error with increased fuel consumption and premature aging of the catalytic converter.
For details, please visit the website FORDBOOK.ru