LR3/Disco 3
The V8 EMS has two knock sensors located in the V of the engine, one per cylinder bank. The sensors are connected to
the ECM via a twisted pair.
The knock sensors produce a voltage signal in proportion to the amount of mechanical vibration generated at each
ignition point. Each sensor monitors the related cylinder bank.
The knock sensors incorporate a piezo-ceramic crystal. This crystal produces a voltage whenever an outside force tries to
deflect it, (i.e. exerts a mechanical load on it). When the engine is running, the compression waves in the material of the
cylinder block, caused by the combustion of the fuel/air mixture within the cylinders, deflect the crystal and produce an
output voltage signal. The signals are supplied to the ECM, which compares them with `mapped' signals stored in
memory. From this, the ECM can determine when detonation occurs on individual cylinders. When detonation is detected,
the ECM retards the ignition timing on that cylinder for a number of engine cycles, then gradually returns it to the original
setting.
Care must be taken at all times to avoid damaging the knock sensors, but particularly during removal and fitting
procedures. The recommendations regarding torque and surface preparation must be adhered to. The torque applied to
the sensor and the quality of the surface preparation both have an influence over the transfer of mechanical noise from
the cylinder block to the crystal.
The ECM uses the signals supplied by the knock sensors, in conjunction with the signal it receives from the camshaft
sensor, to determine the optimum ignition point for each cylinder. The ignition point is set according to preprogrammed
ignition maps stored within the ECM. The ECM is programmed to use ignition maps for 98 RON premium specification
fuel. It will also function on 91 RON regular specification fuel and learn new adaptions. If the only fuel available is of poor
quality, or the customer switches to a lower grade of fuel after using a high grade for a period of time, the engine may
suffer slight pre-ignition for a short period. This amount of pre-ignition will not damage the engine. This situation will be
evident while the ECM learns and then modifies its internal mapping to compensate for the variation in fuel quality. This
feature is called adaption. The ECM has the capability of adapting its fuel and ignition control outputs in response to
several sensor inputs.
The ECM will cancel closed loop control of the ignition system if the signal received from either knock sensor becomes
implausible. In these circumstances the ECM will default to a safe ignition map. This measure ensures the engine will not
become damaged if low quality fuel is used. The MIL lamp will not illuminate, although the driver may notice that the
engine 'pinks' in some driving conditions and displays a drop in performance and smoothness.
When a knock sensor fault is stored, the ECM will also store details of the engine speed, engine load and the coolant
temperature.
ELECTRONIC THROTTLE
The V8 EMS incorporates an electric throttle control system. The electronic throttle body is located on the air intake
