Manual - Chapter 5 - Fuel & Oil

4. Fuel system: Fault finding

1. As will be clear from the general description, the fuel injection system is not, to use modern jargon, user-serviceable. While the fuel injection and ignition system are not of the fully-integrated engine management type that is being fitted to some cars and, in prototype form, to one or two motorcycles, they are interconnected to an extent previously unknown in the motorcycling world; this makes accurate fault diagnosis very difficult. Also their components cannot be repaired and due to the lack of any useful information or test data, they cannot easily be tested by the ordinary private owner. 
2. This means that 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 minimize the risk of a fault in the fuel injection system.
5. Preventative 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.
   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 components which move or become hot, and 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, whilst wires which are too slack may foul other components.
   6. Be careful never to knock, drop, or otherwise mishandle any of the components; all are extremely sensitive and easily damaged. Note that this particularly applies to the injection control unit; always ensure that it is properly secured and that any tools etc carried in the storage compartment above it are well wrapped in rag and secured so that they cannot cause vibration by rattling around. BMW specify that tools are to be carried only in the tail compartment; the underseat compartment is for lightweight items only, such as the first-aid box.
   7. If any component is found to be worn or damaged at any time, repair or renew it immediately, before the damage has a chance to affect any other component.
   8. Whenever any part of the induction system (ie air filter, airflow meter, throttle valve assembly, as opposed to the purely electronic components) is disturbed, always ensure that all joints are sealed airtight on reassembly so that there are no air leaks to upset the mixture balance. All soh rubber seals or hoses should be refitted with great care and retaining clips or hose clamps should be correctly positioned and securely fastened; do not overtighten any clamp or there is a grave risk of distorting the components being secured.
   9. Whenever any part of the fuel system (ie fuel feed and return pipes, fuel rail or injectors) is disturbed, always ensure that all joints are securely fastened on reassembly to prevent the possibility of fuel leaks and of the resulting drop in pressure.
   10. Always clean or renew (as applicable) the fuel filters exactly at the intervals specified in Routine Maintenance or earlier, if necessary; the system is extremely vulnerable to the presence of dirt or water and the engine may stop completely if one or more fuel passages become obstructed by particles of foreign matter. Keeping the filters clean is the only way of preventing this, although great care should always be taken not to allow dirt or water into the fuel tank whenever the cap is opened.
6. If a fault does arise, some clue to the reason may be given by its symptoms; if not consider the problem in a logical manner is an attempt to isolate the fault. In the first place check that there is a good quantity of clean fuel in the tank and that the battery is in good condition and fully charged (check that all other electrical systems are working normally as a quick test of battery condition). It should be possible to hear the fuel pump working, if not check the pump circuit fuse. If the pump is working, check that fuel is present under pressure in the fuel rail and that the surplus is returning via the pressure regulator to the tank. Check also that none of the fuel tank vent hoses are blocked by kinks or foreign matter.
7. If the fault occurs only while the engine is running, there is not a great deal that the ordinary owner can do to isolate it. Checking the appearance of the spark plug electrodes will reveal whether the mixture is excessively rich or lean, but the possible causes of either of these conditions are far too many and varied to be checked without the correct test equipment. Check the components of the fuel and induction system (see above) for air or fuel leaks, check the exhaust system for holes or other damage and check the valve clearances and engine compression to ensure that the engine is mechanically sound. As far as is possible, check that the ignition system is in good order. 
8. When all other possibilities have been eliminated (as far as the ordinary owner can check them) the fault must be assumed to be in the electronic components of the fuel injection system. At this stage the machine should be taken to a good authorized BMW dealer who has the BMW/Bosch diagnostic unit. This equipment is connected to the machine by a set of adapter 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. 
9. Unfortunately there is no alternative to the use of this equipment; while this manual contains all the test data that can be gleaned from BMW's service literature, nothing 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. Do not attempt to test any components using equipment which has its own power source (eg multi meters, ohmmeters, meggers or battery and bulb test circuits) or the applied voltage may destroy one or more of their sensitive circuits.
10. The only permissible use for an ordinary tester is to check the wiring loom for damage. Note, however, that all the components of a particular circuit must be disconnected before the wires of that circuit are checked, to avoid any risk of the sort of damage mentioned above. Particular attention should be paid to the various connectors and any earth connections.
11. Taking all the above into account, many owners may well feel that the simplest course of action is to take the machine to an authorized BMW dealer if a fault of any sort is encountered in the fuel injection 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, a skilled operator will 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.

Next Section: 5: Fuel tank: removal and refitting