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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: Romonobyl on December 26, 2024, 05:02:42 PM
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EDIT: This was a longer read than I intended, I have a habit of over-explaining things so I appreciate the patience.
I have a thread (https://www.motobrick.com/index.php?topic=15888.0 (https://www.motobrick.com/index.php?topic=15888.0)) running on the Project Classic forum immortalizing my epic struggle bringing back a well-aged brick from deep hibernation. Most of the problems were to be as expected and I've made headway there, but I've hit my first wall so I thought I'd make a post here. I already replaced the fuel pump and filter with all new hoses as the old one was long gone. The fuel "level" sending unit was intact but had a lot of surface corrosion which I scoured with contact cleaner and a brush. All the wires ohmed out OK but if it wasn't so $$$ I'd likely get a new one. Regardless I reassembled everything inside the very clean tank and set it on the frame and poured in a gallon of fresh gas.
Here's where Problem #1 popped up. While the tank was off I did I quick survey of the condition of the wiring underneath and found the 5-pin connector from the HES was falling apart; it literally crumbled in my fingers. I color-matched the wires of each pin to the harness and plugged them in individually then protected each with some electrical tape until I decide on a permanent solution. I took the frame ground apart and cleaned that up as well.
Here's the actual issue (finally). I installed a new battery and disconnected the wire to the starter so I could check the pump. Nothing. I was getting power to the fuse but the pump was silent. I pulled it back out for a quick bench test and it was fine so back in it went. This time I reattached the wire to the starter and motored the engine (it spins freely) but it was too loud to hear the pump. I tried again with the starter disconnected and this time the pump worked! I spliced in a pressure gauge and was getting 42 PSI at the injectors. Here's where the tricky part is...sometimes it works, sometimes it doesn't. Today I couldn't get the pump to come on at all so I broke out the multimeter. If I'm reading the diagram correctly the pump relay is controlled by the ignition control unit through the ground wire. This would explain why I would be getting power at the fuse but the pump still not working. I checked for continuity at the negative terminal of the fuel pump (disconnected) to ground with the start button pushed and it was good. I reconnected the wire to the pump and it started working again! I tried a few more start cycles and the pump worked a few times then stopped again.
I pulled the #3 plug to check for spark and never got one, which leads me to the HES and possibly the janky connection that could also contribute to my touchy fuel pump. I did a forum search first thing and got some great info, the next thing I'm going to do is make a new heavier battery ground cable then remove the fuel sending unit again for a closer examination and replace the fuel pump wires as well as reflow the solder connections. I also cleaned the connectors at the fuel injection and ignition control units.
I think the next step will be a deep-dive into the finer details of the hall effect sensor, something tells me that here there be gremlins. If anyone has any advice or can point me in the right direction I would greatly appreciate it, thanks as always.
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Not unheard for the four pin fuel tank connector to get flaky/intermittent.
Here's one possible fix:
https://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/fls.connector/fls.connector.htm
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You have two problems.
You have intermittent power to the pump, likely the plug as duck mentions, check it out.
You have no spark at cylinder three. Check for spark at the other cylinders. If that checks out, hopefully it's just a bad spark plug lead. Then swap it with one of the others as a check.
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You have two problems.
You have intermittent power to the pump, likely the plug as duck mentions, check it out.
You have no spark at cylinder three. Check for spark at the other cylinders. If that checks out, hopefully it's just a bad spark plug lead. Then swap it with one of the others as a check.
If that fuel level sender (along with a new 4-pin connector) wasn't so damned pricey I'd probably replace it as I do believe that could be the problem. I'm going to take it back out and replace the fuel pump wiring and reflow the solder, then I'll look into upgrading that connector.
I will check the other cylinders for spark, clearly I'm still at the baby-step stage.
Thanks for the input.
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I'm thinking, if you haven't got power and earth on both sides of the plug, you might save yourself some time by fixing that before going into the tank.
I'd look at the low tension side of the coils before looking at the hall sensors, but from your photos I can see why you have low confidence in them. Here's a link to some photos of a quick simple way to test the hall sensors.
https://www.k100-forum.com/t15758-starter-issues-k100rs#189161