Author Topic: 87 K100RS START PROBLEM (Read 34034 times)

Inge K. · « **Reply #25 on:** February 04, 2014, 01:48:50 PM »

Quote from: grant71 on February 04, 2014, 12:55:27 PM

please tell me where is the next connection point is, so to speak, so that i can test continuity. would it be from the fuses?

Correct, fuse #6.............next is one of the two terminal 87 at the FI relay socket.

grant71 · « **Reply #26 on:** February 06, 2014, 01:00:46 PM »

thank you Inge. i ll do that next. question: does the battery have to be connected and does ignition have to be on ? ( btw. i see from internet that Norways unleaded petrol costs 2.1 euros per litre )

Inge K. · « **Reply #27 on:** February 06, 2014, 02:37:47 PM »

When testing at the fuse it would be easiest (and best result) to do a voltage check
Battery connected, ignition on and starter button pushed...........you should read ~12V.
If OK, you don't need to check next step...
--------------------------------------------------------------------------------------------------
When checking one of the terminal 87 at the relay socket, relay removed, ignition off,
continuity check between socket and fuel tank connector.
If not OK, check between socket and fuse.....and fuse and Connector.

grant71 · « **Reply #28 on:** February 09, 2014, 12:14:53 PM »

thank you Inge for your advice. i followed your instructions . from tank conn the fuel pump worked. from 87 relay ign on the starter pushed fuel pump worked. from no 6 fuse to relay 87 NO continuity. replaced fuse NO cont. i messed about a bit then got cont after about an hour. i then tried to start motor and fuel pump worked as it should when starting the bike. tomorrow ill put petrol in tank and see if she starts like normal. i cannot pin point the problem. some little electric gremlin. thanks for your interest

Scott_ · « **Reply #29 on:** February 09, 2014, 06:10:17 PM »

almost sounds like the wire connection at the backside of the fuse connection is going bad. Not impossible to happen.

Inge K. · « **Reply #30 on:** February 09, 2014, 08:05:15 PM »

Or the same connectors have become a bit wide and don't grip the male connectors at the fuse
that firmly anymore.

Connect the test probes to the correct 87 terminal at the relay socket and the other end to the
green wire on the fuel tank connector (harness side)........and try to wiggle the fuse a bit.

octobot · « **Reply #31 on:** February 09, 2014, 11:54:54 PM »

Hi
I'm new to the forum, and new to debugging this type of problem, so thanks for your patience in advance.

Interestingly enough, I have a very similar problem to grant71. I too ride a 1987 K100RS, and am having fuel pump problems. When starting the bike, the fuel pump does not "whir". Because of this, and the poor physical condition of the part, I assumed the pump was bad, and replaced it with an aftermarket part. After installing it, I still do not hear pump startup "whir" upon start. When testing for power at the pump I get zero volts. However, testing at the Green/brown wires that connect to the tank under the seat I get 12 volts on startup. This tells me it's something electrical inside the tank (am I correct?). I also get 12 volts when reading at the fuse.
Some additional info. The battery is brand new and fully charged. The tank is nearly empty, with less than a gallon in it. The fuel level warning light is NOT lit, even though the tank is nearly empty. The horn does not work even though the battery is fully charged. When looking at the fuel sender unit through the filler hole, it looks filthy, but I can't tell if it's corroded.
A few questions:
1. Does the fuel sender control the power to the fuel pump? I can infer the answer is yes from some of grant71's statements, but would like confirmation.
2. Will I need to fill the tank to have the fuel pump run? I haven't filled the tank yet, because I don't want to have to drain it again if there's a problem.
3. My tank is nearly empty, why isn't my low fuel light on?
4. Is the fact that my horn isn't working related to my fuel pump problem?
5. Any other suggestions on what to do to have the pump run?

Thanks in advance. Let me know if I should be starting a new thread instead.

Inge K. · « **Reply #32 on:** February 10, 2014, 01:06:21 AM »

Welcome Octobot!

1. The fuel level sender does not control the fuel pump, it just that all the wiring goes through at this common
spot, rather than one wire in each corner of the tank.
2. You don't need to fill the tank before further testing/measuring.
3. This could be related to the problem with your fuel pump.
4. The problem with your horn isn't related to this.
5. As it's a problem with both the low level switch and the fuel pump I would suspect the common ground
connection (fuel level indicator, fuel low level switch and fuel pump is all using the same ground connection) ......measure if you got continuity between the brown wire outside of the tank and the black
wire at the fuel pump.

grant71 · « **Reply #33 on:** February 10, 2014, 08:20:38 AM »

well !! i dont understand the idiosyncracies of electronics. i did nothing specific really and everything came right. thanks for all your input. octo might have hit the nail on the head with the fuse suggestion. problem is now i dont know whether the fault has been rectified permanently. i just hope it wont reappear one cold and wet night on a lonely road. i took the bike for aspin a few minutes ago and she is running superbly.go well and be careful. Grant

octobot · « **Reply #34 on:** February 10, 2014, 09:27:28 AM »

Grant, it was actually Inge that gave the fuse suggestion. :) I hope your problem stays fixed!

Inge, I tested the continuity at the black/brown wire, and there is some resistance. I then tried testing resistance between the pump's positive terminal and external green wire, and there was no resitance (no continuity). Does this mean a bad wire? Any suggestions? Thanks in advance.

grant71 · « **Reply #35 on:** February 10, 2014, 11:38:34 AM »

sorry about fuse credit. i get confused sometimes as to who sends the messages. saw octobot on top somade wrong choice. octobot, my sender was also filthy so i got a good used one which was shiny and clean. i dont know where you are living. i got from JAMES SHERLOCK in UK. solved my fuel pump not working. good luck

octobot · « **Reply #36 on:** February 10, 2014, 12:13:49 PM »

Grant, how did you know that you needed to replace the fuel level sender unit? I did a test as described earlier, and it does seem like the positive lead is having a problem. The negative/ground reads at 0.5 Ohms, the positive reads as 0.L (no reading). Is there anything else you would check? I want to be sure it's truly broken before I order the part.

grant71 · « **Reply #37 on:** February 10, 2014, 02:08:37 PM »

hi octo. i removed the fuel pump from the tank( quite a job for a 1st timer ) connected green to pos battery and brown to neg batt. the fuel pump worked. as i stated previously the sender was rusted but with no apparent wire breaks. fuel sender from James sherlock cost 40 pounds sterling. as i also stated i dont know where you live. in US there must be dozens of used parts dealers. grant

octobot · « **Reply #38 on:** February 10, 2014, 03:37:59 PM »

Grant, as you suggested, I removed my aftermarket pump from the tank and tested with 12V source, and the pump does work. I also tried the same the original Bosch pump, and it did not spin, so at least I know I didn't waste my money in buying a new pump!
I took the aftermarket spade connector off of the positive lead, and tested for continuity again, just to be sure it wasn't a bad spade connection, and still no continuity. I think I'm ready to say that it's the fuel level sender unit wiring. I can't seem to find any of these used online, but I should be able to get the part new from my local dealership.
Thanks for the help!!

rbm · « **Reply #39 on:** February 10, 2014, 03:54:40 PM »

Quote from: octobot on February 10, 2014, 12:13:49 PM

Grant, how did you know that you needed to replace the fuel level sender unit? I did a test as described earlier, and it does seem like the positive lead is having a problem. The negative/ground reads at 0.5 Ohms, the positive reads as 0.L (no reading). Is there anything else you would check? I want to be sure it's truly broken before I order the part.

Octobot,

The fuel level sending unit is electrically independant of the fuel pump, although they share a common ground connection. The sender is a variable resistor whos wiper is attached to an arm with a float. Inside the sender is a fuel level switch. The sender assembly is welded to a metal plate that bolts to the tank. On that plate, you will see that the wire lead enters through a gas tight plastic terminal block. If you were to remove and examine the sender, you'd find that the terminal block has three isolated solder terminals. One is attached to the Green/white wire in the cable and goes to the fuel pump positive (yellow wire inside the tank). Another has a green wire that attaches to the fuel level switch (white wire in the cable). The third terminal attaches to another green wire and goes to one side of the variable resistor (yellow wire inside the cable). The fourth wire in the cable, brown, is electrically attached to the plate, which grounds the tank, the fuel sender wiper and the negative terminal of the fuel pump. You will notice a small solder terminal welded to the plate to which the black in-tank wire is attached.

The only failure points in your problem are (1) loose or broken terminal pin in the connector at the end of the cable, (2) broken brown wire or green/white wire within the cable or at the plate, or (3) broken wire to the pump. (3) is possible since the wires are old and gasoline could have caused hardening and damage to the wires inside the tank. Are the pump wire soft and flexible? (1) is also possible and very likely. The connectors are old and get used often so it is possible that the pins have been pushed up into the connector body and don't make contact. Are the ends of the pins in the connector visible upon inspection?

See if you can take a pin, puncture the insulation on the green/white just beyond the tank connector and test for power from the pin to ground. If you see 12V, error (3) is most likely. If you see no voltage, error (1) is most likely.

It is probably a good idea to remove the float assembly from the tank to allow for inspection and cleaning. I made a write up on how to recondition the fuel sender ( http://www.k100-forum.com/t3349-testing-in-tank-fuel-sender-unit#76423 ). After follwoing my instructions, you still can't refurbish the fuel sender, then it should be replaced.

If you have a broken connector, clip it off and replace it with a AMP Superseal or a standard trailer connector.

octobot · « **Reply #40 on:** February 10, 2014, 05:13:38 PM »

Thanks RBM! What great info...
The casing for the wire is very brittle, in face, a piece broke off, exposing green-corroded wire beneath as I was inspecting it (on the positive lead).
The pins are visible in the connector, and appear shiny.
I re-connected the connector, and pushed my sharp probe of the multimeter under the casing of the green wire (tank side of connector) about 2 inches from the connector, and found ~5 mV with ignition on, and 12 V when starter engaged. I tested again at the pump wire side, and found only a few mV while the starter was running.

So, this leads me to believe that case 3 is the problem... I assume your reconditioning method won't help me since the wire is so corroded, and I'll need to replace the whole fuel level sender part. True?

rbm · « **Reply #41 on:** February 10, 2014, 07:45:59 PM »

False.

I don't think all is lost. Take the sender out and solder on new wires for the fuel pump. Fuel resistant wires are obviously best so maybe ask a local auto parts dealer for advice. An alternative might be to go to a local auto wreckers and snap up some wires from a wreck or to a marine supply shop. You'll want 18GA wires with silicone insulation, not PVC. This fix will be much cheaper than buying a new unit from the dealer. While the unit is on the bench, refurbish it according to my instructions.

The sender I photographed for my instructions had brittle broken wires as well. There were bare spots with exposed wire dangerously close to the strain relief on the body of the sensor. This would have caused a short circuit inside the tank if the wire touched the case. So, I planned on refurbishing my unit but came across a brand new unit for a really good price at exactly the same time, so I replaced my unit. I kept the old one for a spare.

octobot · « **Reply #42 on:** February 10, 2014, 11:52:52 PM »

Excellent! I like this answer better, since it means I don't have to wait 5 days for the part before I can work on this... I'll go on a hunt for the wires tomorrow. Do I need to buy a new o-ring or gasket? In reading some of the related threads here, this seems to be a related gasket: 62161459608,
Thanks again.

octobot · « **Reply #43 on:** February 12, 2014, 02:09:06 AM »

I pulled the fuel level sender unit out of the tank this evening. Boy, was it gunked up with gasoline buildup. Upon inspecting the wires, I found that that positive wire was broken off at the terminal pin. In fact, the entire terminal pin was gone. After carefully cleaning the area, I was able to get a positive continuity test from the nub that was left, but I was unsuccessful at soldering a wire to the nub. There just wasn't enough left to solder to. I was able to get continuity to the wire a couple of times, but when moving the unit, and trying to connect the unit to the pump and wire harness connector, it would inevitably separate. After three tries I gave up. I decided that even if I did get it to work for a few minutes, the bikes vibrations would eventually work it loose.

Alas, I will need to order the part after all. On the bright side, after the failed soldering, I spliced directly into the green wire, and was able to positively test that the pump does run when the starter is running. Hopefully when I put a new sender unit in, that will be the last of my troubles....
Thanks again for the excellent advice, rbm. Not only do I have a confirmed diagnosis, it was fun trying!!!

grant71 · « **Reply #44 on:** February 12, 2014, 01:46:04 PM »

today i put everything together. washed and polished the bike. it gleams like a new penny now. she starts at once and everytime i tried to start which was about 20 times. going beautifully. one query though. my fuel light has stayed on. how many litres of fuel are left on average once the fuel light comes on?

Kyle10 · « **Reply #45 on:** February 12, 2014, 01:54:05 PM »

how many litres of fuel are left on average once the fuel light comes on?

This proportional to your distance from a convenient filling station.

rbm · « **Reply #46 on:** February 12, 2014, 02:22:51 PM »

The light should come on with 4 litres in the tank (approximately). Sounds like you might have a short to ground somewhere in the cable leading from the fuel sender to the instrument cluster. To sanity check, disconnect the tank plug from the harness and measure resistance between the white wire and ground. If you have a low amount of fuel (< 4 litres), there should be continuity to ground; infinity if the fuel level is over the minimum level. If you measure infinity with the fuel you have in the tank, then you need to troubleshoot wiring. The short might be in the instrument cluster or might be within the harness.

johnny · « **Reply #47 on:** February 12, 2014, 02:39:41 PM »

they are all different... my old 94k1100rs would go 35 miles after the light came on... my current 94k1100rs will only go 20 miles and my current 96k1100rs will only go 25 miles... i wanna fill up before the light comes on cause i thinks the lower you run the tank the more likely you will experience a fuel pump failure on down the road...

j o

octobot · « **Reply #48 on:** February 19, 2014, 11:23:34 PM »

She lives!! I got my fuel level sender unit in the mail today, and installed it. I needed to coax it to start a bit by spraying starter fluid into the air intake (air cleaner taken out), but after that it screamed back to life immediately! I forgot what a great sound that is....
Now to figure out what's wrong with my horn.
Thanks to all for your advice and help!

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Author Topic: 87 K100RS START PROBLEM (Read 34034 times)