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'92 R100GS power failure


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I'm really inexperienced at this stuff, particularly in regard to electrical/ignition issues. I'm desperate for help.


Initially I was riding my 92 R100GS about 10 miles, when the bike just died as I was riding it. When I tried to re-start it, the engine turned over, but it wouldn't fire up. It turned out that the there was no spark at the plugs.


In trying to troubleshoot why the plugs were not sparking, I made a very stupid and rash decision. The plugs in the bike are Bosch Super RO 668's. This morning, suspecting that something might have been wrong with it, I removed the right cylinder plug and replaced it with an older one, a Bosch RO 948. I left the 668 in the left cylinder, and fired the bike up. It turned, and then ... I lost all power a second later, and still don't have any.


Now when the key is turned on and the kill switch is also on, I get an intermittent electric buzzing sound from one of the relays. But if the kill switch is off, no buzzing.




I replaced the one of the two black relays that was making the buzzing sound.


Still no power.



And, after fu..ing up by turning the bike over with two different plugs which preceded the power failure, I put in two brand new plugs (matching, of course).


No power.



And, the battery voltage is 13 volts, but there is NO voltage at the coils (some actually, but in millivolts).



By the way, the ignition coil is brand spanking new. Also, when I initially only had the problem of no spark at the plugs, I WAS getting voltage to the coils. Now, after fu..ing up by using two different plugs, there is NO voltage to the coils.



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First, using two different spark plugs will not have caused any problem.


For the lack of ignition, there are a few possibilities. The following is just preliminaries to get a sense of where to go next -- with additional information we can help with a logical diagnostic progression.


Your vintage of R100 has electronic ignition -- a small electronic box under the tank that fires the coils/spark plugs, and a "can"-shaped ignition sensor on the front end of the camkshaft (the same place the older airheads had a set of mechanical ignition points). The electronic ignition module is mounted on the right side of the main frame backbone, on a bracket sticking out perpendicular to the backbone.


Before you assume either is bad, first trace the wires between the two to verify this is not something as simple as a wire break or a loose connection.


WARNING: DO NOT REMOVE THE FRONT ENGINE COVER BEFORE DISCONNECTING THE BATTERY! Doing so can result in the front cover contacting the diode board at the front top of the engine and creating a dead short that sends a massive wallop of battery current through the diode board, burning it out. :(


While you have the tank off, and before you remove the front cover, turn on the key and the kill switch to see whether you can narrow down the source of the buzzing.


Also while you are in there, check the heat transfer compound under the ignition module -- it dries out over the years and needs to be renewed. If the ignition module overheats, it shuts down. (Given that your engine doesn't start after the module has cooled, this is not likely the problem, but it is mentioned as an oft-neglected maintenance item that should be addressed anyway, independent of the present problem.)


Do you have a manual, such as a Haynes? You should -- really invaluable for pictures of the components and more importantly, a comprehensive color-coded wiring diagram.


Let us know what you find with the visual inspection, and we can proceed from there -- other airhead-knowledgeable folks will also chime in.

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