A highly advanced 3rd generation full engine management system the MEMS system was developed by Rover in partnership with Motorola. While it is based on the general principals and experience gained with the Motorola single point system fitted to the early single point injection 820 models it is both more advanced and robust and is generally regarded as highly reliable system. Unlike the earlier single point system no fuel or ignition settings are held in volatile memory.
Most of the sensors employed (coolant temperature, crankshaft angle, knock sensor) are generic types and have electrical characteristics similar to those detailed for the Lucas equipped models. As with the Lucas system the Manifold Absolute Pressure sensor (MAP) is integral with the ECU. The normal mode of operation for the MEMs system is closed loop using a Lambda O2 sensor in the exhaust downpipe to provide feed back. The system also uses an ambient air temperature sensor to determine the correct mode of operation.
In many ways this is a simpler system
to maintain than the Lucas Hotwire, the throttle by-pass stepper motor
is much less prone to problems and the idle speed stop rarely needs altered,
however without a suitable serial communications tool it is less DIY friendly
than the Lucas system and maintenance is limited to checking the various
sensors are operating correctly and have sound electrical connections.
Simple Checks
Before carrying out any of these test check the engine is in generally good condition, the plugs and plug gaps are in good order, the plug leads are good, the airfilter is clean, the inlet manifold is tight and not drawing air and the engine is reaching full correct working temperature.
- (1) Check the alternator is charging, all connections are tight and the battery has a good state of charge.
- (1) Check the small bore pipe between the inlet manifold and the ECU is clear, this pipe is long (particularly on the 200/400 series). Disconnect at BOTH ends before blowing through to avoid damaging the MAP sensor. Take care not to break the connection which protrudes from the ECU. Check the rubber connecting hoses are in good order.
- (2) Remove and examine the distributor cap and leads, replace the rotor arm if it is a early type with steel insert, the later type arms have an all plastic body may also have a red paint mark.
- (3) Clean the coil, it appears to be in a position (particularly on 200/400 models) where it collects much dirt and debris.
- (4) With engine full warm and at idle speed unplug the coolant temperature sensor (CTS); if the engine speeds up it generally indicates that the sensor is good however the resistance can be checked properly against the tables values given for the CTS for the Lucas Hotwire system using a suitable low cost Digital Multi-Meter. This is an negative temperature coefficient thermistor sensor resistance decreases with temperature
- (5) Check the voltages at the throttle position sensor (TPS); Supply 5 volts, earth return 0 volts, Output; 0.5 volts throttle closed to 4.5 volts fully open, varying smoothly over full range of throttle positions. Unlike the earlier Lucas Hotwire system this is not user adjustable.
- (6) Ambient Air Temperature Sensor (ATS); resistance-temperature characteristics are similar to the NTC thermistor sensor used for the CTS.
- (7) Lambda Probe output, the voltage should pulse rapidly between about 0.2 and 0.8 volts, and good sensor in a system which is operating in closed loop mode should show a signal which "switches" (sic) between high a low values at least once per second. New sensors generally respond at around 3 Hz as they age they slow to around 1 Hz - slower than 1 Hz and the sensor should be replaced as it may cause high exhaust emissions and MOT test failure. WARNING Do not under any circumstances connect an ordinary moving coil multimeter to the Lambda sensor output only a high impedance device such as a Digital Multimeter is suitable. As these area available for less than 10 UK Pounds from Maplin and other electronic suppliers I strongly recommend anyone working on car electrical system to buy one.