Computer controlled catalytic converter for Fiat 500 and Fiat 126
With the catalytic converter, the vehicles conform to the Euro 1 standard which reduces annual tax remarkably. Due to electronic regulation, the catalytic converter, which is integrated into a sport exhaust pipe, reduces petrol consumption as well.
Since some years there is a gerneral operating licence (GOL) for our controlled catalytic converter for the Fiat 500 and Fiat 126. This document replaces the previous German TÜV certificate. The gerneral operating licence is up to the latest standards.
1. The entire system and its function
With the Fiat 500 and Fiat 126's uncontrolled carburettor engine, the carburettor alone determines the composition of the petrol-air-mixture.
In order to positively avoid overheating and engine knocking, the carburettor discharges a slightly rich mixture most of the time. Under certain operating circumstances, the mixture is too rich.
An ideal exhaust emission control can only take place if the petrol-air-mixture is constantly adjusted to Lambda 1. This, on the other hand, can only be guaranteed with a lambda sensor and regulator system that monitor and adjust the exhaust gas composition. Otherwise, the petrol-air-mixture becomes too rich when accelerating (too much petrol, which causes the development of nitrogen oxides).
As this regulating process is so important, uncontrolled catalytic converters can only clean about 45% of the exhaust fumes, whereas computer controlled catalytic converter systems can clean 90-95%.
The feedback air-fuel-ratio control system regulates the petrol-air-mixture, maintaining a stoichiometric ratio of 1kg petrol to 14.7 kg air (= about 12000 litres) which is the ideal ratio for the catalytic converter.
The regulator is not exactly adjusted to Lambda 1. It oscillates between rich and lean about twice per second.
During the rich phase, the catalytic converter requires the oxygen which was stored during the lean phase. With the backfit Fiat 500 / 126 carburettor engines the base mixture is rich: the standard carburettor delivers rich mixture - no backfitting of the needle valves is necessary!
The lambda probe, installed in the exhaust gas flow, diagnoses Lambda < 1 (the engine is running on rich mixture). The probe then sends a voltage signal (0.9 volt) to the computer, which in turn switches 12 volts onto the air valve that is attached to the flange below the throttle valve.
Supplementary air (secondary air) flows into the vacuum-zone of the intake pipe, which makes the mixture more and more lean, until Lambda > 1 is measured. The voltage signal of the probe drops to 0.2 volt, thus the air valve is turned off and closes. The flow of secondary air is cut off, which makes the mixture more rich.
The whole thing happens at least once and up to three times per second.
Of course, the computer also features some other finesses, for example it ensures a smooth engine idle.
2. The matrix, coating and function of the catalytic converter
The catalytic converter's matrix is a honeycomb with longitudinal channels, made of metal. The channels are coated with a ceramic washcoat, containing platinum and rhodium. These noble metals are the actual catalytic converter. They accelerate the conversion of HC, CO and NOx without changing themselves.
So the catalytic converter is not simply a particle filter. HC and CO are incinerated, the nitrogen oxides are split into oxygen and nitrogen. The oxygen that is set free is required for the incineration of HC and CO particles. For this reason, the toxic gases need to be in an ideal ratio (Lambda = 1).
Because there are three reactions taking place at once, the catalytic converter is often called "three-way catalytic converter". The catalytic converter requires unleaded fuel, as the lead can cover the catalytic coating in the course of time thus causing deterioration.
3. Frequently asked questions (FAQ)
We hope to have answered most of the questions.
Should you have any further questions, please feel free to send an email to: service
4. Catalytic converters for other vehicles
At the moment, we can offer computer controlled catalytic converters for Fiat 128 and X19, as well as for 127, 131, Ritmo, Regata, Uno, Tipo, Fiorino and some derived models.The description of the way it works, as well as a list of frequently asked questions you can find here. For other Fiat models, please feel free to send us an e-mail or call us on 0049 8141/53486-0.