Chapter 1 Routine maintenance and servicing

Ignition system 5B•3flux can pass between the magnet and thesensor. When a trigger vane segment is in linewith the sensor, the magnetic flux is divertedthrough the trigger vane, away from thesensor. The sensor detects the change inmagnetic flux and sends an impulse to theEEC IV module. Additional data is receivedfrom the engine coolant temperature sensor,manifold absolute pressure sensor, inlet airtemperature sensor, throttle position sensorand vehicle speed sensor. Using thisinformation the EEC IV module calculates theoptimum ignition advance setting andswitches off the low tension circuit via theignition module. This results in the collapse ofthe magnetic field in the coil which generatesthe high tension voltage. The high tensionvoltage is then fed, via the coil HT lead andthe carbon brush in the centre of thedistributor cap, to the rotor arm. The voltagepasses across to the appropriate metalsegment in the cap and via the spark plug HTlead to the spark plug where it finally jumpsthe spark plug gap to earth. It can be seenthat the ignition module functions basically asa high current switch by controlling the lowtension supply to the ignition coil primarywindings.In the event of failure of a sensor, theEEC IV module will substitute a preset valuefor that input to allow the system to continueto function. In the event of failure of theEEC IV module, a “limited operation strategy”(LOS) function allows the vehicle to be driven,albeit at reduced power and efficiency. TheEEC IV module also has a “keep alivememory” (KAM) function which stores idle anddrive values and codes which can be used toindicate any system fault which may occur.Distributorless ignition systemsThe main ignition system componentsinclude the ignition switch, the battery, thecrankshaft speed/position sensor, the ignitionmodule, the coil, the primary (low tension/LT)and secondary (high tension/HT) wiringcircuits, and the spark plugs.The system used on carburettor models istermed DIS (Distributorless Ignition System),and on fuel injection models E-DIS, (ElectronicDistributorless Ignition System). The primarydifference between the two is that the DISsystem is an independent ignition controlsystem while the E-DIS system operates inconjunction with the EEC IV enginemanagement module which also controls thefuel injection and emission control systems.With both systems, the main functions ofthe distributor are replaced by a computerisedignition module and a coil unit. The coil unitcombines a double-ended pair of coils - eachtime a coil receives an ignition signal, twosparks are produced, at each end of thesecondary windings. One spark goes to acylinder on compression stroke and the othergoes to the corresponding cylinder on itsexhaust stroke. The first will give the correctpower stroke, but the second spark will haveno effect (a “wasted spark”), occurring as itdoes during exhaust conditions.The ignition signal is generated by acrankshaft position sensor which scans aseries of 36 protrusions on the periphery ofthe engine flywheel. The inductive head of thecrankshaft position sensor runs just above theflywheel periphery and as the crankshaftrotates, the sensor transmits a pulse to theignition module every time a protrusionpasses it. There is one missing protrusion inthe flywheel periphery at a pointcorresponding to 90° BTDC. The ignitionmodule recognises the absence of a pulsefrom the crankshaft position sensor at thispoint to establish a reference mark forcrankshaft position. Similarly, the time intervalbetween absent pulses is used to determineengine speed.On carburettor engines, the ignition modulereceives signals provided by informationsensors which monitor various enginefunctions (such as crankshaft position,coolant temperature, inlet air temperature,inlet manifold vacuum etc). This informationallows the ignition module to generate theoptimum ignition timing setting under alloperating conditions.On fuel injection engines, the ignitionmodule operates in conjunction with theEEC IV engine management module, andtogether with the various additionalinformation sensors and emission controlcomponents, provides total control of the fueland ignition systems to form a completeengine management package.The information contained in this Chapterconcentrates on the ignition-relatedcomponents of the engine managementsystem. Information covering the fuel, exhaustand emission control components can befound in the applicable Parts of Chapter 4.PrecautionsWhen working on the ignition system, takethe following precautions:a) Do not keep the ignition switch on formore than 10 seconds if the engine willnot start.b) If a separate tachometer is ever requiredfor servicing work, consult a dealerservice department before buying atachometer for use with this vehicle -some tachometers may be incompatiblewith these types of ignition systems - andalways connect it in accordance with theequipment manufacturer’s instructions.c) Never connect the ignition coil terminalsto earth. This could result in damage tothe coil and/or the ignition module.d) Do not disconnect the battery when theengine is running.e) Make sure that the ignition module isproperly earthed.f) Refer to the warning at the beginning ofthe next Section concerning HT voltage.2 Ignition system - testing2Warning: Voltages produced byan electronic ignition system areconsiderably higher than thoseproduced by conventionalignition systems. Extreme care must betaken when working on the system withthe ignition switched on. Persons withsurgically-implanted cardiac pacemakerdevices should keep well clear of theignition circuits, components and testequipment.Note: Refer to the precautions given inSection 1 of Part A of this Chapter beforestarting work. Always switch off the ignitionbefore disconnecting or connecting anycomponent and when using a multi-meter tocheck resistances.1 If the engine turns over but won’t start,disconnect the (HT) lead from any spark plug,and attach it to a calibrated tester (available atmost automotive accessory shops). Connectthe clip on the tester to a good earth - a boltor metal bracket on the engine. If you’reunable to obtain a calibrated ignition tester,have the check carried out by a Ford dealerservice department or similar. Any other formof testing (such as jumping a spark from theend of an HT lead to earth) is notrecommended, because of the risk ofpersonal injury, or of damage to the ignitionmodule.2 Crank the engine, and watch the end of thetester to see if bright blue, well-defined sparksoccur.3 If sparks occur, sufficient voltage isreaching the plug to fire it. Repeat thecheck at the remaining plugs, to ensurethat all leads are sound and that thecoil is serviceable. However, the plugsthemselves may be fouled or faulty, soremove and check them as described inChapter 1.4 If no sparks or intermittent sparks occur,the spark plug lead(s) may be defective. Also,on distributor systems, there may beproblems with the rotor arm or distributor cap- check all these components as described inChapter 1.5 If there’s still no spark, check the coil’selectrical connector (where applicable), tomake sure it’s clean and tight. Check for fullbattery voltage to the coil at the connector’scentre terminal. Check the coil itself (seeSection 3). Make any necessary repairs, thenrepeat the check again.6 The remainder of the system checks shouldbe left to a dealer service departmentor other qualified repair facility, as there is achance that the ignition module maybe damaged if tests are not performedproperly.5B1595Ford Fiesta Remake