Hey all, I could use some help diagnosing why I am unable to get my K100 started.

I've rebuilt my 87 K100 RS fully. I am at the point that I am trying to get it started again. The bike ran before the rebuild.
Here's where I am at.

It appears that the bike won't get the fuel pump to push fuel to the injectors, maybe not enough power is getting to the fuel pump?

Bike cranks but no sign of firing.
Verified there is spark.
Air meter is connected.
Bench tested FI Relay, clicks when 12V is applied.
Fuse #6 is in good shape.
All grounds have been cleaned and I believe are grounding properly.
Bench tested fuel pump, found it is gunked up so I bought a new one and bench tested it, it works.
Fuel sending unit has proper resistance, tank level meter is a bit beaten up but works. 
Checked the plug from the harness to the fuel sending unit, it receives power when cranking. I cleaned the pins and the female end of the plug as best as I could.
Battery is charged fully.
Power is received to the brown and black wires for the fuel pump, about 8V when cranking. Tested with a multimeter outside of the fuel tank.


Anything I should check again or you think I am missing? Thanks!

Longshot... fuel line reversed on tank connections.

Also, if you squeeze the fuel line between your fingers one should be able to feel a pulse of the pressure in the line.

The fuel pump isn't pushing any fuel to the line or fuel rail when I crank the bike. I've looked through multiple posts to verify that I have the lines correct.

Check to see if there's power at the fuel pump when cranking. The smaller diameter terminal on the fuel pump is 12V and larger diameter is ground.

Sometimes the power connection in the base of the fuel level sender fails.

The front pipe goes to the fuel pressure regulator.
The rear pipe goes to the fuel rail.

You can remove the fuel pump to test it or you can jump power to it in the tank to see if it whirs.

Thank you for the suggestion but I have tried that. I get about 8V to the black wire for the fuel pump black wire from the fuel sending unit when I crank, verified on a multimeter. The fuel pump isn't whirring on when I crank. I know the pump works because i have bench tested it. Maybe that isn't enough power to run the pump enough? its about 10*F right now so the battery is getting low. I put it back on a trickle charger to try again later. There's a chance my battery is due to be replaced and isn't providing enough power to the pump to get it going. Anyone know how much power is required to get the pump running? I thought i saw somewhere 9.6V was required but i can't verify.

I'd need someone more knowledgeable to verify if they believe the fuel sending unit is at fault here. I followed this video to test the unit. https://www.youtube.com/watch?v=olvmd95Pd0k and i was getting comparable resistance readings.

'87... does the fuel tank have a single bolt to secure it or does it have a pair of horrible C-clips to hold it down? It makes a difference because with the early fitting you could have the loose plug syndrome (forward-left under the tank).

diceweiss wrote:Bench tested FI Relay, clicks when 12V is applied.
Power is received to the brown and black wires for the fuel pump, about 8V when cranking.

A bench-tested relay may click but when installed, inputs could be weak, some of its outputs might not function, or wires running from those outputs could be compromised.

Although you bench-tested your fuel pump and it worked, and presumably have verified correct connections to the pump itself when in the tank, it's fair to say a 12V fuel pump trying to pump fuel may not work well or at all on 8V, and one that does function may not deliver fuel through clogged tank hoses or a clogged fuel filter if those items were not part of your rebuild.

It won't be the first time a pump bench tested fine but caused issues in the tank....eventually finding a wiring defect at the square connector plate under the tank [assuming its the later 2 clip tank].

Other thoughts...blocked or wrong way filter?

Two thoughts here:

First, you didn't mention changing the fuel filter.

Second, and more likely from my experience, you may have a bad connection in the tank connector(been there a couple times).  Make sure the contacts in both the male and female parts are clean.  It may help if you distort the contacts to help them make a good connection.

Dai wrote:'87... does the fuel tank have a single bolt to secure it or does it have a pair of horrible C-clips to hold it down? It makes a difference because with the early fitting you could have the loose plug syndrome (forward-left under the tank).

Only 85 and earlier K100s have the tank that bolts down at the rear and early fuel sender in the front left corner. All 86+ K100s and all K75s have the fuel sender with the ping pong ball float.

Ah! Old man's memory

Dai wrote:Ah! Old man's memory

I am there, too.  Can't for the life of me remember the last time my memory worked.

Point-Seven-five wrote:Two thoughts here:

First, you didn't mention changing the fuel filter.

Second, and more likely from my experience, you may have a bad connection in the tank connector(been there a couple times).  Make sure the contacts in both the male and female parts are clean.  It may help if you distort the contacts to help them make a good connection.

My bad, i didn't think to list it but the fuel filter is brand new and in the correct orientation. I've tried cleaning both sides of the plug for the fuel sending unit with a clean pipe cleaner that's used for paint guns. The prongs on the female part of the connector look consistent. ( 3 metal tabs pointed toward the center) I'll take another stab at cleaning them further.

Laitch wrote:

Diceweiss wrote:Bench tested FI Relay, clicks when 12V is applied.
Power is received to the brown and black wires for the fuel pump, about 8V when cranking.

A bench-tested relay may click but when installed, inputs could be weak, some of its outputs might not function, or wires running from those outputs could be compromised.

Although you bench-tested your fuel pump and it worked, and presumably have verified correct connections to the pump itself when in the tank, it's fair to say a 12V fuel pump trying to pump fuel may not work well or at all on 8V, and one that does function may not deliver fuel through clogged tank hoses or a clogged fuel filter if those items were not part of your rebuild.

It sounds like I should be getting 12V to the fuel pump and am down on power to it. I'll test to see if I am getting the amount of voltage needed at the FI relay and check the hoses for any blockage.

If you suspect a weak battery you can hook up jumper cables to a car. I've done that to get a K started before.

The only hitch is that you have to be very careful not to cause any shorts with that 12V+ jumper cable.  If memory serves when I did it I removed the battery hold down plate on top of the battery.

It's a long story but one night I jumped started a K1100 from a car at a rest stop in middle of nowhere Kansas at around midnight.

Quick update.

I ran 12V of power through the connector of the sending unit with the fuel pump attached, it'll whir on.

I verified my battery is charged and checked the voltage to the male plug of the connector ( the connector on the wiring harness) Its reading 11V when I turn the key on. When pressing the starter, that voltage dips to 9V. Going off of Laitch's previous comment, that leads me to believe I need to work backwards to the FI relay and check that it is getting 12V to the female plug for the relay

Can someone confirm if that is the logical next step? I'm trying to follow the EFI troubleshooting guide but with my lack of electrical knowledge, looking at the flow chart doesn't explain how to test pin 87 on the relay so I'm struggling.

Thanks.

87 is power out to the fuel injectors and to Fuse 6. Fuse 6 then goes to the fuel pump and thermo relay.

When the fuel relay is triggered those should get power.

When the key is turned on, the fuel relay is triggered by the YEL/BRN wire being grounded from Pin 7 of the ICU (ignition control unit) when the engine turns. The ICU knows the engine is turning when it gets pulses from the Hall Effect Sensor.

9V is definetely not enough to run the pump.
Besides the new pump and filter, change also the inner fuel hoses. They may leak and into the fuel, you can't easily see it. Do not use basic hoses, they have to be specific hoses to be in immersion, with inner and outer protective layers.

Fuel line for internal use in the fuel tank must be SAE J30 R10 rated for immersion.  Also, make sure to use the proper fuel injection hose clamps.  The fuel line usually has a 13mm.  Get the clamps at the same time you get the line and you will have the right size.

JBT and Point-Seven-Five, thanks for the advice. I'll replace the hoses once I get it started, the OEM clamps in the tank look new so I'll reuse those. 

I may have ruled out the connector too early. I think the male end of the plug isn't making a solid connection as I have 11.58V on the one end, and can apply 12V to the fuel sending unit to get the pump to fire but, when the connector is together, nothing. I ordered a 4pin Deutsch connector to replace it.

I'll probably get some deoxit and go through all of the electrical connections after this and clean them up further.

I'm looking for a fuel sending unit for a 93 k1100 LT if anybody knows where I can get one would be a big help a project has been dead in the water.
The one I had was nonfixable I took it out of the tank and looked at it it was so corotted it was brittle and falling apart

One of the BMW breakers (junkers??) is going to be your only bet, unless you happen to come across one on ebay. They're rare and expensive which is why various members spend so much time trying to figure out how to fix them; expect to pay around $100 s/h and $220 for a new one from Motorworks

https://www.motorworks.co.uk/fuel-level-sensor-fua59565-3.html

Yes, im aware of theimited availability for them.
Even pache charging ove $300 are lut ofstock.
Can you recommend the name of a few boneyards i could try?
Thank you for your response

Darrell Clark wrote:I'm looking for a fuel sending unit for a 93 k1100 LT if anybody knows where I can get one would be a big help a project has been dead in the water.
The one I had was nonfixable I took it out of the tank and looked at it it was so corotted it was brittle and falling apart

Try Thom at https://kpartsholland.com/ .  Shipping to contenetal USA wasn't as high as I expected and he has come through for me sevral times!

Will do, thanks for the heads up

Update:

Found this gem of a thread in case anyone needs it in the future or needs a good explanation on how to diagnose some of the things I was struggling with  : https://www.k100-forum.com/t1686-fuel-pump-not-powering-up
(Thank you Crazy Frog for the writeup in this post for novices like me)


Replaced the under-tank connector with a new Deutsch connector
Pin 86 of FI relay receives 12V with ignition on
Pin 85 of FI relay receives -12V with ignition on
Pin 30 of FI relay receives 12V regardless of ignition on or off, and when starter is going
Power to Fuse #6 receives 12V on each side of the fuse
Boosted the battery and tested Fuse 6 again, increase in voltage reading but no difference
Unplugging idle switch / throttle position sensor does not change anything
Haven't tested injectors recently but they were cleaned prior to disassembling the bike - not concerned about those until verifying the pump whirs
Checked resistance of water temperature sensor, 9.8K Ohms at ~ 0 Celsius  - have an extra one i can test if that appears abnormal
No light on the cluster for the water temp sensor
It appears on the electrical side of things I'm in good shape

I did find that one of the pins on the female side of the FI relay was dislodged from the housing, allowing it to push down when the FI relay was pushed in, likely causing an incomplete connection.

Currently under the impression this may have been the culprit all along. Will test tomorrow when my kid isn't sleeping and report back. - If this is my issue, I have K Put to thank from that link above for putting that in the thread!

Pin 85 is not -12V. It is 0V which is ground.

How relays work:

When you ground pin 85 and pin 86 is 12V it connects the 12V power in, Pin 30, to 12V out to what you're powering via Pin 87.

Duck, you're right. I was copying how things were written on the previous post.

I tested everything and the issue remains the same. However, I did realize that the TGPI connector and the under tank connector are identical. It is possible i mislabeled them when I tore everything down, as i used painters tape to label each connector and i did have a few fall off at one point. Thus I may have had them hooked up to the wrong connector this entire time...

Can someone confirm on the harness side, what colors are in the 4 pin connector to the fuel sending unit? Is it green/white, brown, yellow, and white? OR green/yellow, black/yellow, brown, and yellow/white?

If it is green/white, I'm an idiot who just learned a whole lot about diagnosing problems  haha

Thanks for the help from everyone so far!

The wire colors are the same on both sides of the connector:

Tank:
GRN/WHT - fuel pump power (to GRN for some fuel level senders)
BRN - ground
WHT - Cluster idiot light
YEL - Fuel gauge (if equipped)

Gear indicator switch:
YEL/BLU
YEL/BLK
YEL/WHT
BRN

diceweiss wrote:If it is green/white, I'm an idiot who just learned a whole lot about diagnosing problems  haha

I'd disagree with that. Only an idiot doesn't learn from making mistakes.

Dai wrote: Only an idiot doesn't learn from making mistakes.

I disagree with that. Narcissists can be intelligent and accomplished but don't learn from their mistakes either because they don't make any. Mistakes are caused by faults in everyone around them.

Dai wrote:

Only an idiot doesn't learn from making mistakes.

Experience teaches us things that we never wanted to know in the first place.

Duck, Dai, and Laitch, thanks for the support. I certainly FEEL like an idiot for this one. Great news, that was the culprit! Mislabeled harness connector had me for a loop. This would be a good note to add into the EFI troubleshooting guide so others don't make such a silly mistake.

Time to put everything back together and get this old brick started for the first time in almost two years!