Manual - Chapter 6 - Ignition system

11. Ignition system: fault-finding

  1. Although electronic ignition systems are by now familiar equipment to most motorcyclists, the lack of test data on the system fitted to these machines, and its interconnection with the fuel injection system, means that there is very little the ordinary owner can do to test or repair it if a fault should arise.
  2. As with the fuel injection system, the emphasis must be more on preventing faults from arising in the first place than on actual remedial repair work. The simplest approach can be summed up as follows:
    1. If the system is working properly, leave it alone.
    2. Prevention (in the form of preventive maintenance) is better than cure.
    3. In the event of a fault. take the machine to an expert.
  3. The first of these is obvious, but worth stressing. Do not attempt to 'tune', modify or 'improve' the system in any way. The only maintenance necessary is set out below and in the Routine Maintenance section of this manual; at all other times the system should not be disturbed.
  4. The second is by no means as contradictory as it might first appear; the electronic components themselves are generally very reliable and any faults are usually caused by disruption of the current flow between the various components or by external factors such as excessive heat, vibration or attack by foreign matter or corrosive chemicals. Therefore anything that can be done to ensure that all components receive a stable supply of the correct amount of electrical current, that they are kept clean and properly secured to protect them from excessive heat and/ or vibration, and that they are kept free of dirt, corrosion and substances such as water, coolant, brake fluid, battery acid or engine oil which might cause damage, must help to minimise the risk of ignition failure.
  5. These preventive measures can be summed up as follows:
    1. Ensure that the battery electrolyte levels are correct and that the terminal connections are clean and securely fastened at all times. If the machine is not used for any length of time, ensure that the battery is given refresher charges to keep it in good condition
    2. Working through the relevant wiring diagram to ensure that all components (including individual connectors) are treated, carefully clean back to bare metal all connections and terminals (finishing off with proprietary contact cleaner to remove any grease or oil) then pack them with silicone grease to exclude water and dirt and to prevent corrosion. On reassembly ensure that, where applicable, the waterproof cover is correctly refitted over each connector plug and that the retaining clip is secured. The ignition and kill switches should be packed with silicone grease or regularly lubricated with WD40 or similar to protect their terminals.
    3. Ensure that all frame earths and earth connections are completely clean and securely fastened. Where wires are connected to the frame earth point, or at the bellhousing/ frame mounting joint. ensure that the frame paint is scraped away to provide a clean metal-to-metal joint and that silicone grease or similar is applied to prevent corrosion.
    4. Ensure that all components are correctly positioned and securely fastened at all times, also that all are as clean and dry as possible.
    5. All wiring must be correctly routed so that it runs in smooth loops but avoids all possible contact with sharp edges, control cables or other moving components and components which became hot in operation. The wiring must be secured out of harm's way, using plastic cable clips or insulating tape. Remember that wires which are too tight or sharply kinked may fail due to the effects of vibration, but wires which are too slack may foul other components. The HT leads must be routed with particular care to prolong as much as possible their service life, and the spark plug cover should be fitted at all times to protect the plugs, caps and leads from dirt, water and other debris.
    6. Be careful never to knock, drop or otherwise mishandle any of the components; all are extremely sensitive and easily damaged.
    7. If any component is found to be damaged or faulty at any time, repair or renew it immediately, before the damage has a chance to affect any other component. Note that if the HT coils, suppressors, HT leads or spark plug caps are renewed at any time, only genuine BMW parts must be used to ensure that the replacements are compatible with each other and with the control unit. If non-standard components have to be fitted in emergency, ensure that their resistance values are the same as the genuine items; if incompatible items are fitted the different resistance values may well damage the HT coils or the ignition control unit. Only the specified type and grade of spark plug should be fitted; seek the advice of an authorised BMW dealer or similar expert before making any changes from standard specification. Ensure also that the spark plugs are regularly serviced and/or removed as described in Maintenance - Minor Service - Check and adjust the spark plugs; wrongly-gapped or worn-out plugs may overload the control unit.
  6. If a fault does arise, first read Section 2 concerning the precautions to be taken to prevent personal injury or damage to the machine when carrying out test procedures. To isolate the fault, check through the system in a logical sequence; while different faults may require varying methods, the following sequence of tests should permit the tracing of most faults (as far as the ordinary owner is likely to be able to follow them):
  7. Check that the battery is in good condition and fully charged - while it is possible, as a quick check, merely to ensure that all the other systems are working normally, it should be remembered that the battery may well be only just able to turn the engine over on the starter motor without having the reserves necessary to power the ignition and fuel injection systems. Therefore in certain circumstances it may be preferable to use a meter to check the battery rather than more rough and ready methods.
  8. Check that the ignition and engine kill switches are properly switched on and that both are functioning correctly, also that the load-shedding relay is correctly cutting off the other circuits.
  9. If the starter motor will not turn over, check that the fault is not in one of the ignition system-related safety interlock components (refer to the relevant wiring diagram tor details).
  10. If the starter motor is functioning correctly but the engine will not start, remove the spark plugs, connect each to its cap and lay it on the cylinder head or cylinder head cover. Be careful to place the electrodes as far away as possible from the spark plug apertures and to cover each aperture with a wad of rag or similar to prevent the risk of fire from sparks igniting any fuel/air mixture that may be ejected. Also ensure that the metal body of each spark plug is firmly in contact with the metal of the cylinder head or cover so that the risk of damage to the ignition system is avoided, which might result if one or more of the spark plugs is not correctly earthed during the performance of this test. When the engine is turned over on the starter motor (taking great care to prevent the risk of personal injury, as warned in Section 2), a strong blue spark should appear at regular intervals across the electrodes of each plug.
  11. If no spark appears, or if the spark appears thin or yellow, further investigation will be required. First of all, substitute brand new spark plugs of the correct type and grade, then repeat the test to check whether any improvement is obtained. If the fault occurs on one cylinder only. swap the complete HT lead assembly (right angled suppressor/connector, lead, spark plug cap and spark plug) with that of another cylinder to check whether this cures the fault. Note however (on 100 models only) that if cylinders 1 and 4, or 2 and 3, are faulty at the same time the problem is most likely to be in the appropriate HT coil or its connections; this can be checked easily by swapping over the coil connections and repeating the test.
  12. All of the HT lead components can be tested as described in Section 6 of this Chapter, but for the purposes of a quick check the various components can be tested by disconnecting them and swapping between cylinders until the faulty item is isolated; it is extremely unlikely that the same fault would cause failure in all three or four of any of these components.
  13. If the fault is thought not to be in the HT lead assemblies, check the coils themselves. If all their connections and mountings are secure and there is no visible sign of damage, the power supply can be checked, as described in Section 5; a 12 volt bulb can be substituted if a meter is not available. The only full test for the HT coils that can be carried out by the ordinary owner is described in the same Section, but requires the use of a meter.
  14. If the power supply to the coils is not correct, check the ignition and engine kill switches for faults, also the battery and earth connections (see the relevant wiring diagram for details).
  15. If the coils are receiving the correct power supply and if there is no apparent fault in the coils themselves or in the HT lead components, the fault must lie in the ignition trigger assembly or in the control unit, or in the wires between them. It is worth checking that the trigger assembly is securely fastened and in the correct position, also that the connections are secure and the wires in good condition. It is permissible for the private owner to use an ordinary multimeter to check the wiring for faults, provided that all ignition system or fuel injection system components have been first disconnected. Refer to Section 2.
  16. If none of the checks outlined above reveal the cause of the fault, the machine should be taken to an authorised BMW dealer who has the tester/diagnostic unit developed for BMW by Bosch. This equipment is connected to the machine by a set of adaptor leads and should be capable of checking the function of the entire ignition and fuel injection systems; in skilled hands it should be able to trace faults very quickly and easily.
  17. Unfortunately there is no real alternative to the use of this equipment; while this manual contains all the relevant test data, nothing additional is available which will allow the checking of the system's components using ordinary equipment. Since all other available data is related specifically to the Bosch diagnostic unit it is of no use to anyone who does not have access to one of these units. The only other possibility is to test by substitution; since the ignition system has only two major components it is feasible for an ordinary owner to swap first the trigger assembly, and then, if necessary, the control unit, in an attempt to isolate a fault. This is a very inconclusive and unsatisfactory test procedure which of course presupposes that sound components of exactly the correct type are available, either from a friendly BMW dealer or from a friend's machine.
  18. Taking all the above into account, many owners may well feel that the simplest course of action is to take the machine to an authorised BMW dealer if a fault of any sort is encountered in the ignition system. Compared with the time-consuming nature of the various tests and the dangers both to the machine and its owner inherent in some of them, the idea must be attractive of having a skilled operator quickly and safely run through a test sequence on the diagnostic unit to check the entire system and locate any faults, even if this does mean having to pay the labour charge necessary.