Chapter 1 Routine maintenance and servicing

1595Ford Fiesta Remake4E•2 Exhaust and emission control systemsinto the engine induction system and thenceinto the combustion chambers. Thisarrangement eliminates any fuel mixturecontrol problems. The operating principles forthe system used on the Endura-E engine arebasically the same as just described withrevisions to the component locations andhose arrangement.On CVH and PTE engines, a closed-circuittype crankcase ventilation system is used, thefunction of which is basically the same as thatdescribed for the HCS engine type, but thebreather hose connects directly to the rockercover. The oil filler cap incorporates aseparate filter in certain applications.On Zetec engines, the crankcase ventilationsystem main components are the oilseparator mounted on the front (radiator) sideof the cylinder block/crankcase, and thePositive Crankcase Ventilation (PCV) valve setin a rubber grommet in the separator’s lefthandupper end. The associated pipeworkconsists of a crankcase breather pipe and twoflexible hoses connecting the PCV valve to aunion on the left-hand end of the inletmanifold, and a crankcase breather hoseconnecting the cylinder head cover to the aircleaner assembly. A small foam filter in the aircleaner prevents dirt from being drawndirectly into the engine.Evaporative emissions control systemThis system is fitted to minimise the escapeof unburned hydrocarbons into theatmosphere. Fuel evaporative emissionscontrol systems are limited on vehiclesmeeting earlier emissions regulations;carburettor float chambers are ventedinternally, whilst fuel tanks vent to atmospherethrough a combined roll-over/anti-trickle-fillvalve. On vehicles meeting the more stringentemissions regulations, the fuel tank filler capis sealed, and a charcoal canister is used tocollect and store petrol vapours generated inthe tank when the vehicle is parked. When theengine is running, the vapours are clearedfrom the canister (under the control of theEEC IV engine management module via thecanister-purge solenoid valve) into the inlettract, to be burned by the engine duringnormal combustion.To ensure that the engine runs correctlywhen it is cold and/or idling, and to protectthe catalytic converter from the effects of anover-rich mixture, the canister-purge solenoidvalve is not opened by the EEC IV moduleuntil the engine is fully warmed-up andrunning under part-load; the solenoid valve isthen switched on and off, to allow the storedvapour to pass into the inlet tract.Pulse-air systemThis system consists of the pulse-airsolenoid valve, the pulse-air valve itself, thedelivery tubing, a pulse-air filter, and on somemodels, a check valve. The system injectsfiltered air directly into the exhaust ports,using the pressure variations in the exhaustgases to draw air through from the filterhousing; air will flow into the exhaust onlywhen its pressure is below atmospheric. Thepulse-air valve can allow gases to flow onlyone way, so there is no risk of hot exhaustgases flowing back into the filter.The system’s primary function is raiseexhaust gas temperatures on start-up, thusreducing the amount of time taken for thecatalytic converter to reach operatingtemperature. Until this happens, the systemreduces emissions of unburned hydrocarbonparticles (HC) and carbon monoxide (CO) byensuring that a considerable proportion ofthese substances remaining in the exhaustgases after combustion are burned up, eitherin the manifold itself or in the catalyticconverter.To ensure that the system does not upsetthe smooth running of the engine undernormal driving conditions, it is linked by thepulse-air solenoid valve to the EEC IV module,so that it only functions during engine warmup,when the oxygen sensor is not influencingthe fuel/air mixture ratio.Catalytic converterCatalytic converters have been introducedprogressively on all models in the range, tomeet the various emissions regulations.The catalytic converter is located in theexhaust system, and operates in conjunctionwith an exhaust gas oxygen sensor to reduceexhaust gas emissions. The catalyticconverter uses precious metals (platinum andpalladium or rhodium) as catalysts to speedup the reaction between the pollutants andthe oxygen in the vehicle’s exhaust gases, COand HC being oxidised to form H 2 O and CO 2and (in the three-way type of catalyticconverter) NO x being reduced to N 2 . Note:The catalytic converter is not a filter in thephysical sense; its function is to promote achemical reaction, but it is not itself affectedby that reaction.The converter consists of an element (or“substrate”) of ceramic honeycomb, coatedwith a combination of precious metals in sucha way as to produce a vast surface area overwhich the exhaust gases must flow; the wholebeing mounted in a stainless-steel box. Asimple “oxidation” (or “two-way”) catalyticconverter can deal with CO and HC only,while a “reduction” (or “three-way”) catalyticconverter can deal with CO, HC and NO x .Three-way catalytic converters are furthersub-divided into “open-loop” (or“unregulated”) converters, which can remove50 to 70% of pollutants and “closed-loop”(also known as “controlled” or “regulated”)converters, which can remove over 90% ofpollutants.In order for a closed-loop catalyticconverter to operate effectively, the air/fuelmixture must be very accurately controlled,and this is achieved by measuring the oxygencontent of the exhaust gas. The oxygensensor transmits information on the exhaustgas oxygen content to the EEC IV enginemanagement module, which adjusts theair/fuel mixture strength accordingly.The sensor has a built-in heating elementwhich is controlled by the EEC IV module, inorder to bring the sensor’s tip to an efficientoperating temperature as rapidly as possible.The sensor’s tip is sensitive to oxygen, andsends the module a varying voltagedepending on the amount of oxygen in theexhaust gases; if the inlet air/fuel mixture istoo rich, the sensor sends a high-voltagesignal. The voltage falls as the mixtureweakens. Peak conversion efficiency of allmajor pollutants occurs if the inlet air/fuelmixture is maintained at the chemicallycorrectratio for the complete combustion ofpetrol - 14.7 parts (by weight) of air to 1 partof fuel (the “stoichiometric” ratio). The sensoroutput voltage alters in a large step at thispoint, the module using the signal change asa reference point, and correcting the inletair/fuel mixture accordingly by altering the fuelinjector pulse width (injector opening time).Removal and refitting procedures forthe oxygen sensor are given in Parts B, Cand D of this Chapter according to fuelsystem type.2 Exhaust system - renewal2Warning: Inspection and repairof exhaust system componentsshould be done only afterenough time has elapsed afterdriving the vehicle to allow the systemcomponents to cool completely. Thisapplies particularly to the catalyticconverter, which runs at very hightemperatures. Also, when working underthe vehicle, make sure it is securelysupported on axle stands.If the exhaust system components areextremely corroded or rusted together, theywill probably have to be cut from the exhaustsystem. The most convenient way ofaccomplishing this is to have a quick-fitexhaust repair specialist remove the corrodedsections. Alternatively, you can simply cut offthe old components with a hacksaw. If you dodecide to tackle the job at home, be sure towear eye protection, to protect your eyes frommetal chips, and work gloves, to protect yourhands. If the production-fit system is stillfitted, it must be cut for the servicereplacementsystem sections to fit. The bestway of determining the correct cutting point isto obtain the new centre or rear section firstthen, with the old system removed, lay thetwo side by side on the ground. It should nowbe relatively easy to determine where the oldsystem needs to be cut, and it can be markedaccordingly. Remember to allow for theoverlap where the two sections will plugtogether.