1 Another poor soul with the intermittent stalling issue Sat Feb 28, 2015 1:31 am
kringb
Silver member
The bike is a 1985 k100.
Here are the basic symptoms:
When driving at a speed of anywhere between 45 and 75 (more often than not. Sometimes, although rarely, at slower speed) it would loose all power. The battery and oil light do not initially come on but the speedometer still showed electrical power. In the beginning, it would just momentarily cut out and then, after a heartbeat, surge back to life. Lately it has been stalling and it will take a little longer to restart.
It felt exactly as if the fuel was being momentarily cut off. Because of this I originally thought it was a fuel pump or filter problem but I have since ruled those out.
Because the problem only shows itself while driving, I can only troubleshoot it while driving. So, I connected a fuel pressure gauge to the line before the fuel rail and taped the gauge to the top of the tank. When it stalls there is no loss in fuel pressure. It remains correct.
So my next step was to hook up an led test light to one of the fuel injectors. It showed that when it stalls there is no power being sent to the injector. I then hooked up the test light to the injector pin #12 on the EFI computer. It also showed no power when the bike cuts out.
My thinking at this point was that either the efi computer is faulty, or something that informs the computer (like the airflow meter) might be faulty, or a wiring short between the two. If it was a wiring short then wouldn't the problem occur more randomly at any speed?
I opened up the air box and tested the continuity of the wires from the air flow sensor to the efi computer connector. I wiggled the wires around a lot but they each measured ok. I flipped the air sensor vane back and forth and it appeared ok to me. So I changed the air filter and put everything back together. It could be coincidence but after messing with the air box the problem did not appear for about two weeks. This is true to the intermittent nature of this problem so I really can't say that it is related to anything I did with the air box, as much as I would like to.
I have also cleaned the electrical connections at the electronic ignition controller under the tank and the ground near to it, the connection to the efi computer, and the connections to the air sensor, and the water temp sensor connection. I also ruled out the idle switch. The problem occurs i when plugged in or not.
So that is where I am at. I'm not sure what to do next. I'd like to test the air sensor or the efi computer but I am not sure how to test either while I am riding. Can anyone suggest a way to do so? I don't think the problem would appear on a bench test. Swapping parts would be great but I don't have a spare k100.
I still have a lot to learn about electronics and this bikes fuel control system. That is why I am turning to this forum. I'd appreciate any help I can get.