1986 K75C Cranking but Not Starting - Suspect Fuel Pump

[Heezea]

Hey guys, the brick (1986 K75C) stopped working. I think it may be the fuel pump. I'd been having trouble with her running; she totally died on me three times on the interstate but fired right up when I hit the start button so I was able to ride home. A few days later after doing some research I tried to start her with no luck. Couple more days later, she finally fired up and I let her idle for about 2 minutes when she just died. Now it doesn't sound like she's even trying to fire. I do have very solid crank. I tested the battery at 12V but I wanted make sure it was strong even when starting, so to eliminate the battery being the problem, I hooked up the car charger and charged at 2 amp over night then set it to 10 amp trying to start.

I don't think I hear the fuel pump run when I turn it on or when I try to start. I hear some humming when I try to start but I think that's the starter. I do hear a relay click off a few seconds after letting off the start button. I tried a jumper wire from the battery + to fuse #6 as detailed in this thread: http://www.k100-forum.com/t1686-fuel-pump-not-powering-up. Still didn't hear the fuel pump though? I unplugged and tested the left 4-pin under-tank connector (which I cleaned a few months back with contact cleaner and a brass brush) at the green and white wire and had a solid 12V. I also plugged it back in and backprobed the green/white wire, getting 12V.

I should mention that I've stripped her down and traded the instrument cluster for a more simple speedo with RBM's help and his control board. Also, the previous owner removed the ignition key and installed a toggle switch. I haven't had any electrical problems other than the 4-pin fuel connector I cleaned a few months ago, which immediately worked perfectly after cleaning. I put about 1500 miles since I got her from the previous owner and she's been running really nicely.

Can I be pretty certain it's the fuel pump at this point? I read some things about the fuel sender unit but not sure. If anyone can help me figure out what to do next, I'd appreciate it.

[Laitch]

I don't think I hear the fuel pump run when I turn it on or when I try to start. I hear some humming when I try to start but I think that's the starter. I do hear a relay click off a few seconds after letting off the start button.

The pump will not run when you turn the ignition switch to On. It starts operating when the starter button is pushed and will keep operating if the engine starts running.

You should hear the pump emit a high-pitched sound for a couple of seconds when you let off the starter button if the engine doesn't start. If you don't hear that sound, the pump isn't operating correctly. If you have ascertained that the pump is getting current from the wire at the fuel level sender then you'll need to remove the pump and bench test it. Is the tank clean?

[Heezea]

Thanks Laitch for your response. What you are saying about the starter button is in line with what I had read and was listening for. I had my ear pressed to the tank and couldn't hear anything there. I was afraid bench testing the pump was the next step but if the pump needs to be replaced then I'll have to remove it anyhow so may as well get on with it. The tank is very clean and I've been regularly refueling with fresh gas. Though while I have the pump out I'll go through everything else. All the fuel hoses look good too, I'm pretty sure the PO changed all of them.

[Heezea]

Well, I've made some progress by process of elimination, but still not running.

1. I pulled the fuel tank and bench tested the fuel pump. The fuel tank is seriously almost spotless and everything looks great in there. I tested first by connecting directly to the fuel pump and the pump worked. Then I tried by connecting - to brown and + to green/white at the male end of the connector attached to the tank; pump worked. Then I reinstalled the tank and tried again, bike cranked good but wouldn't start, same problem. I guess the pump is running though I still swear it doesn't sound like it. I disconnected the connector again and tested the voltage at the female end (brown and white/green); got a little less than 12V, same as before.

2. I tested two of the fuel injectors with an LED connecting to - at the battery and the probe in one of the connector sockets. Got a nice solid light.

3. I tried removing the FI connector and giving it a good cleaning with electrical cleaner and toothbrush.

4. While the tank was removed, I noticed that the S-hose was looking pretty rough so I went ahead and removed the air box and put in a new hose. I was happy to do this but I must've rerouted the throttle cable while doing this because now I have a ton of slop on the throttle. Guess I'll get the throttle readjusted next.

5. I was planning on testing to see if I have spark next by removing a spark plug and checking if I see a spark.

6. I also plan on cleaning the start button assembly.

7. If I have spark, then I suppose I should check fuel pressure next.

Will report back when I've exhausted the options. If anyone has any thoughts, please let me know.

[Laitch]

1. I pulled the fuel tank and bench tested the fuel pump. The fuel tank is seriously almost spotless and everything looks great in there. I tested first by connecting directly to the fuel pump and the pump worked. Then I tried by connecting - to brown and + to green/white at the male end of the connector attached to the tank; pump worked1. Then I reinstalled the tank and tried again, bike cranked good but wouldn't start, same problem. I guess the pump is running though I still swear it doesn't sound like it.

If it doesn't sound like the pump is working, what does it sound like? Does it have any sound at all? If the fuel cap assembly has been removed, you should be able to see fuel returning and probably hear the pump, too when there is 12V at the pump.

Do you have 12V at the wiring indicated by the arrow in the diagram when the starter button is pushed?

[Martin]

The four pin connector is a known source of intermittent problems. Mine was fine for 24 years, then it started to play up so I went out and bought the new 2 part DeoxIT. It worked fine for about a week and then played up again fiddling with it bought it back to life. However now I didn't trust it and as it had broken down next to the local electrical supply place I took this as a sign from Asgard and bought a new waterproof one. Another mate has constant problems with his connector but insists on trying to fix it by flattening pins and cleaning it with phosphoric acid. This works for a while but eventually it fails. He keeps at it though. When I first got my Brick I was working with an ex BMW Harley tech. His advice was when I picked it up was to go over all the electrical connectors and clean and grease them with dielectric or silicone grease. The only electrical connection problems I've ever had, were twice on the one connector I didn't clean (now cleaned) it was hard to get to. One battery isolator connector due to not fitting a spring washer and the four pin connector and that's in 26 years.

Regards Martin.

[The Mighty Gryphon]

While making assumptions is an easy way to get in trouble, I assume that you are assuming the four pin tank connector is working properly...

As alluded to in Martin's post, that damn connector is one of the most prolific sources of trouble on Motobricks.

[rbm]

If you have a voltmeter, do a quick test.  Set the voltmeter to read 12V DC.  Put Black lead of the VM on the harness-side Brown wire of the pump connector, the Red lead on the Green/grey wire of the same connector.  Turn on the ignition. The VM should read 0V DC.  Press the start button and the voltage should jump close to 12V DC.  Release the button and observe the VM.  It should continue to read about 12V DC for 1.5 seconds after releasing the start button and then drop to 0V DC.

If it does this, you've validated the starting circuit as operating correctly.  The problem is further up the line -- pump connector, fuel sender gas tight connector, wiring or pump are the culprits.

[Heezea]

Wow guys thank you so much for all the great feedback you guys rock.

Ok so I really have no idea what is going on. First Laitch, super good call on taking the cap off to listen to the pump (not sure why I didn't think of this the first time I took it off). So I wasn't crazy, the pump was definitely not running when I press the start button. To double check the pump works, I connected the male end (tank side) of the 4-pin connector brown wire to -battery and green/white to +battery; pump ran fine. I take this to mean the sender and pump are good.

I messed around with a bunch of stuff that didn't really tell me anything as I tried to wrap my head around what is going on.

The last thing I did was what rbm detailed. Test 1: testing the female end of the connector (harness side, not tank side) with the volt meter, VM Black to brown and Red to green/white. The VM continued to read 0 volts while I pressed the start button. I guess when I tested the female side two days ago, Test 2: I had VM Black on -battery and VM Red on green/white of the connector. I just ran out to the garage to recheck Test 2 and I get a very brief (1 second or less) reading of 12 V then nothing. Does the fact I read something in Test 2 but nothing in Test 1 mean I have a bad ground?

[rbm]

Is fuse 6 blown, or making poor contact?

[The Mighty Gryphon]

Regarding your result on Test #1, I suggest you go back and repeat the test.  I suspect that you may not have made contact with your test probe on the brown wire socket on the connector.  On female connectors I sometimes insert a slightly bent piece of wire into the connector and read from it.  The reason for this is that sometimes the conducting part of the connector is recessed a bit and the tip of the probe can't touch it.

Another possibility is that the wire has pulled loose from the contact in the connector.  In the process of unplugging the tank connector I know I have caught myself pulling on the wires instead of the connector body.  I wouldn't be surprised if a previous owner pulled on those wires hard enough to break a joint in the connector. 

That connector sucks.  When I look at how many they used on the ABS system, I am amazed that my brakes still work.

[The Mighty Gryphon]

Another thing to try on that brown wire at the tank connector would be to carefully stick a pin into the wire just ahead of the connector and do test #1 again.  That will tell you if the wire is good and the problem is in the connector.

[Martin]

For the amount of problems caused by the 4 pin connector. And the stuffing around I and others have gone through trying to get it to work consistently. And I came to the conclusion pretty quickly I would replace it as a matter of course. For the $20.00 and hour it took I now have peace of mind. Any electronic store should be able to supply one.
Regards Martin.

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[Laitch]

To double check the pump works, I connected the male end (tank side) of the 4-pin connector brown wire to -battery and green/white to +battery; pump ran fine. I take this to mean the sender and pump are good.

Is fuse 6 blown, or making poor contact?

By testing, Heeza has established that the connector to the fuel level sensor and the pump is ok. Now Heeza should determine if the harness side of the connector is ok by first replacing fuse #6 and cleaning its socket. If that doesn't restore reliable function then the harness side connector should be disassembled and the multimeter used on the bare wires. If that test shows continuity then the connector should be replaced with a reliable unit as both Martin and Gryph have been recommending.

[johnny]

greetings...

if i gotts 1 $ usd everytime somebody replaced their fuel pump when it was something else... my crypto account would be tremendously enormous...

hold on... it already is..

paypal to crypto... you can do it... we gotts this... ping me...

j o

[Heezea]

rbm was correct, the fuse was blown. This must've happened when I was connecting random shit to random shit trying to figure out what the hell is going on with those little dudes running around in the wires making shit work. I've ordered some 7.5 amp fuses but have a 5 amp one in there temporarily. I really don't understand how you guys knew it was the fuse from the basic testing I did. It'd be cool if somebody could explain in really basic terms but suffice to say, you guys are wizards.

Having replaced the fuse I repeated Test #1 and got good voltage around 12 V. So I guess that eliminates everything from the female (harness side) plug back. Since wiring direct to the male end of the plug engaged the pump, that eliminates everything from the male end forward. Leaving....just the god damn male to female connection. A big thank you to everyone who pointed this out, sorry I'm dense but I though by back-probing the male end I could test it, but that probably just pushes stuff around and gives false readings.

I had ordered a set of connectors from Amazon for redoing some of the connectors on parts I've swapped out. I think I read that rbm switch a lot of them out during his build so I figured I'd likely have to do the same.

Installation in progress! Will report back when done. Do you guys recommend putting just a touch of solder on these type of connectors once the wire is crimped on?

[rbm]

Good you found the blown fuse.

It is bad practice to solder a crimped connection.  The solder will wick up the wire leads under the insulation and make the connection brittle.  Best is to use proper crimping tools and proper crimping technique; I know that this is not always possible though.

[The Mighty Gryphon]

The connectors are designed to NOT use solder.  Solder creates a stiff point in the wire where vibration and flexing can weaken the strands and make them break.

[Heezea]

Sweet, glad I asked actually cause I was leaning toward soldering but now I know better. I did buy one of those IWISS crimpers, so the crimps are coming in good and I'm giving them a little pull to make sure they're sturdy.

[Heezea]

She lives! Thanks to everyone that helped, couldn't have done it without you! All in all a pretty simple thing but I put in like three evenings of work to get this troubleshot and fixed. I did learn a ton about the bike so overall, a good experience.

greetings...
if i gotts 1 $ usd everytime somebody replaced their fuel pump when it was something else... my crypto account would be tremendously enormous...

Lol johnny, no joke man, I almost did it but Motobrick.com and it's fine members saved me.

[Heezea]

Dammit son I just sent you mop cabbage in April. But you are right, I probably saved like $500 from the help I just got via this forum where all the best brickers are. Glad to kick in some more, on the way!