I have a 2001 Harley Davidson Road King with a good amount of kilometers. The engine light goes on and it does when slowing down.
Sveral trips to the Harley-Davidson dealer resulted in replacement of the fuel filter, uel line and checking the valves, fuel pump relay, intake manifold gaskets, spark plugs and plug wires, crank position sensor, camshaft timing sensor, engine temperature sensor.
The engine light still lit and the motorcycle seemed sluggish, but at least it didn’t die anymore.
The last time I picked it up, the speedometer wasn’t working and turn signals didn’t cancel. After starting, the engine light stayed lit, then it died again. Tried to restart and all I got was a backfire and black spark-plugs.
After three trips to the dealer, they can’t find a solution. Of course, it runs well in the shop and they can’t duplicate an intermittent problem; but it’s still these. A replacement CPU is apparently no longer available…
Obvious I’m not very happy, the motorcycle purchase price was well over 2 million Thai baht, while the repair cost trying to fix the problem are now as high as I could buy a simple big bike cruiser from Honda or Kawasaki with money to spare.
Gremlins are extremely frustrating for customers and technicians alike. I’ve spent hours troubleshooting only to find an obscure part causing intermittent problems. One of my biggest challenges was on a ‘80s iron-head Sportster that was backfiring on one cylinder.
After replacing many parts and thinking I fixed the problem, I had the same backfire. I heard tachometers could cause spark issues on this mode. I was puzzled how they related, until I looked at the wire diagram. The tachometer received a signal from the coil to indicate rpm.
Over time, vibration would break the contacts in the tachometer, and the coil would ground through the tachometer instead of the spark-plug, but only at certain levels of vibration. I saw spark when cranking it over, but hadn’t accurately identified the problem. A new tachometer fixed the problem. I would not have figured out the root cause and prevented a recurrence without the experience of others.
I’m not sure about Thai Harley-Davidson mechanics, but I doubt they very active on the world wide web outside Thailand, and therefore some of the knowledge can be missing.
Fortunately, your Harley-Davidson model doesn’t us the same circuit as the ‘80s Sportster and with current ignition systems, the carbon would have to thick before it misfire, so that is unlikely. Black plugs indicate a park plug issue or a rich mixture causing fouling.
Misfiring is commonly caused by air leaks, bad fuel or lean running conditions. It could be a restricted injector or low pressure from the fuel pump; however, it sounds ike the dealership relaced all the components.
The issues you mentioned with the signals and speedometer indicate an electrical problem, but if the running problems existed before the last service, they are probably separate issues. The signal and speedo may be due to the technician leaving a coupler disconnected or the contact my have oxidized. It may not have been the technician’s fault for the break in contact but they should have caught it during a test ride and vehicle inspection…..