Exhaust System: Description and Operation

Exhaust System

Vehicles with 2.0L Zetec-E engine






Vehicles with 2.0L SPI engine





Part 1 of 2





Part 2 of 2

NOTE: The exhaust systems are production systems.

NOTE: Support wraps that are removed from the flexible pipe should be retained for future use.

The exhaust systems are of a three-piece construction for production and four-piece construction for service.

Catalytic Converter
The catalytic converter fitted to the Focus range resembles a small muffler. Because of the high temperatures at which the catalytic converter operates, the vehicle body areas around the catalytic converter are protected by heatshields. The catalytic converter controls three emissions; Hydro carbons (HC), carbon monoxide (CO) and oxides of nitrogen (NOx).

Catalyst deactivation due to poisoning
Sulphur (S) in the fuel can cause deactivation of the catalyst.
Lead (Pb) in fuel can cause a severe deactivation at levels above 5 mg per liter of fuel. It is therefore essential that vehicles with catalytic converters always operate on unleaded fuel.
Zinc (Zn) and phosphorus (P) present in some oils, can cause deactivation if oil consumption is high.
The effect of sulphur is felt most if it is released from the catalytic converter as hydrogen sulphide (H2S). This has an unpleasant odor similar to rotten eggs. Changing the fuel manufacturer may help in reducing this phenomena.
To minimize H2S emissions, it is essential that the idle CO level is within specification and that the engine emission system is functioning correctly.

CAUTION: If temperatures exceeding 900°C are achieved the catalyst substrates will start to deteriorate. It is important that the cause is defined and rectified if subsequent melts are to be prevented.

Catalyst melts are normally accompanied by loss of power due to excessive back pressure.
High substrate temperatures are caused by the ignition or the fuel systems.
Misfires at high engine speed may result in an almost instantaneous melt.