My K75S up and died on me ...

[breyfogle]

Riding home from work yesterday afternoon, I stopped at a gas station near home. Filled the tank, paid for the gas, and started (or tried to) the bike to leave for home. Hitting the starter button produced lots of starter noise but absolutely no indication of any hint of ignition what-so-ever. DARN !! K-bikes are supposed to almost unbreakable and mine had been running great right up until I shut it off for gas.

Anyway, it did not take to long to determine that the fuel pump was not running. If the fuel pump failed, the bike had to towed home. If there was an electrical fault maybe I could jury-rig something to get home. After studying the wiring diagram, I figured that I could easily hot wire the fuel pump directly off the battery. (For anyone in a similar situation, a short legnth, 12 inches or so, of wire from the battery + terminal on the left to either side to fuse number 6 will bypass the fuel pump relay and apply 12 volts directly to the fuel pump).

Tried it and the pump spun fine and the bike started as easily as K75's are supposed to start ! Got home OK but I have not yet tried to determine why the fuel pump stopped receiving volts. Could be a simple wire or plug related fault. Could be the HES but I doubt it since the bike ran fine before and after. Could be the ignition module or the computer, hope not ($$$$+ hard to diagnose).

Anyone want to suggest where I might begin tracing this problem down?

[jdiaz]

I'd start with the plug connection under the right side panel. Make sure the female receptacles are gripping tightly.

[Burnszilla]

I'd start with the plug connection under the right side panel. Make sure the female receptacles are gripping tightly.

I second that emotion. That connector always came loose on my old S.

[breyfogle]

I second that emotion. That connector always came loose on my old S.

The plug was recently replaced. Besides, the way I hot-wired the pump routed power thru the plug. It has to be OK.

[BuddingGeezer]

Check Fuel Pump Relay under the tank.

Ralph Sims

[Burnszilla]

Fuse?

[Gilly]

Check Fuel Pump Relay under the tank.

Ralph Sims

What Ralph said.
I would also consider the ignition switch as a common failure, but not like this (usually no-crank). Get that diagram out again and check out the signal to the relay, if that's good check the output side. Could also bench-test the relay, not a hard thing to do.

Gilly

[breyfogle]

Check Fuel Pump Relay under the tank.
Ralph Sims

Had a chance to do a little troubleshooting this afternoon. FIrst, the FP relay works on the workbench. A spare FP relay also works on the bench. It appears that (if I follow the circuit diagram correctly, I'm no electronics wiz) the relay's control input should get switched battery voltage. I does. The control output is an open-to-ground circuit going to the ignition module. Presumably, the IM grounds this connection when it wants the fuel pump to run, thereby closing the relay control circuit which in turn closes the relay's primary power circuit, connecting the fuel pump to battery voltage. From what I can tell, the IM is not grounding its connection to the relay.

I think the next step is to determine if there is a break in the IM to relay control wiring or if the IM has failed. Sound rational ?

[116318]

I had a 93 K75 and the problem was a dirty kill switch . sprayed some wd40 and it cured it.

[Burnszilla]

Sounds like you know what you're doing. I had a 87 K75S that I had spent a lot of time fixing. I fixed the problem by purchasing an R1200GS.

[OfficerImpersonator]

Sounds like you know what you're doing. I had a 87 K75S that I had spent a lot of time fixing. I fixed the problem by purchasing an R1200GS.

Now that's just plain cruel:brow

Not that I don't enjoy spending less time laying on the garage floor ever since I swapped the '92 K75S for a R1150RT-P... :bolt

[Gilly]

Had a chance to do a little troubleshooting this afternoon. FIrst, the FP relay works on the workbench. A spare FP relay also works on the bench. It appears that (if I follow the circuit diagram correctly, I'm no electronics wiz) the relay's control input should get switched battery voltage. I does. The control output is an open-to-ground circuit going to the ignition module. Presumably, the IM grounds this connection when it wants the fuel pump to run, thereby closing the relay control circuit which in turn closes the relay's primary power circuit, connecting the fuel pump to battery voltage. From what I can tell, the IM is not grounding its connection to the relay.

I think the next step is to determine if there is a break in the IM to relay control wiring or if the IM has failed. Sound rational ?

Yes, I'd say you're on the right track, check wire from fp relay to the ignition control module.
Gilly

[breyfogle]

Sounds like you know what you're doing. I had a 87 K75S that I had spent a lot of time fixing. I fixed the problem by purchasing an R1200GS.

I'm almost at that point also. Been futzing with one thing after another for 18 months or so. A new F800S sure looks better and better every day.

Anybody interested in trading the down payment on a F800S for one 18 year old, not currently running, K-bike that also needs a transmission transplant ?

[Burnszilla]

I'm almost at that point also. Been futzing with one thing after another for 18 months or so. A new F800S sure looks better and better every day.

Anybody interested in trading the down payment on a F800S for one 18 year old, not currently running, K-bike that also needs a transmission transplant ?

I have a K75 tranny for sale. PM me if you want it.

[breyfogle]

Update:

I spent most of today swapping out the Ignition module with a known good spare (Thank you BeemerBoneyard !). With the spare IM installed, the fuel pump relay control lead from the IM shorts to ground as soon as the engine cranks over on the starter. Voltage appears at the fuel tank pigtail connector (green with white). Basically eveything works as it should.

As a double check, I uninstalled the good IM and reinstalled the original. Now hitting the starter does not result in the relay control shorting to ground and no voltage appears at the pigtail connector. Problem has to be the IM. Put the BBY IM back in and reassembled everything and the bike starts and runs like a K-bike should.

FWIW, the failed IM is ALSO a used module that replaced the factory original 6-7 years ago. I'm now on my third Ignition Module !! K-bikes don't seem to have much of a history of faulty IM's that i am aware of, I'd be interested in hearing from other high mileage K75 owners about any Ignition module related problems.

Also, what makes a new OEM Ignition Module worth $900 list !!. I can but a whole PC for that. Without a source of used parts at reasonable prices, this failure would not have been worth fixing. The bike would most likely been written off as unrepairable. What a waste.

[BuddingGeezer]

Also, what makes a new OEM Ignition Module worth $900 list !!. I can but a whole PC for that. Without a source of used parts at reasonable prices, this failure would not have been worth fixing. The bike would most likely been written off as unrepairable. What a waste.

A little joke is that HD in Harley Davidson means 'hundred dollars'. I have learned that BMW stands for 'Bring More With'ya' or Break My Wallet'.

Ralph Sims

[kennyD]

The exact same thing happened to me the other day. Stopped the bike and no start no crank on fuel pump.
I will attempt all suggestions below and keep you posted.
Thanks to all for the ideas.

[Kayseventyfive]

Why does the fuel pump need an ignition module to tell it to go round and round? How about rewiring things so the fuel pump runs off the ignition switch?

You know, like a car.

[deilenberger]

Why does the fuel pump need an ignition module to tell it to go round and round? How about rewiring things so the fuel pump runs off the ignition switch?

You know, like a car.Likely for safety reasons. If the bike crashes, and the FI hoses are pulled loose - the engine stops and the fuel pump keeps pumping gasoline, it could get interesting. And I don't know of any cars currently made that have the fuel pump running off the ignition switch. ALL modern BMW cars - the fuel pump is controlled by the engine control unit.

[Kayseventyfive]

Likely for safety reasons. If the bike crashes, and the FI hoses are pulled loose - the engine stops and the fuel pump keeps pumping gasoline, it could get interesting. And I don't know of any cars currently made that have the fuel pump running off the ignition switch. ALL modern BMW cars - the fuel pump is controlled by the engine control unit.

Still thinking workaround, here.......an oil pressure switch would shut off the fuel pump when the engine stopped. I think the Vega had a combination idiot light and safety switch.

Would Germany's finest choke on a part from America's worst? :)

[deilenberger]

Still thinking workaround, here.......an oil pressure switch would shut off the fuel pump when the engine stopped. I think the Vega had a combination idiot light and safety switch.

Would Germany's finest choke on a part from America's worst? :)The same switch would have to power it on for starting.. which is where the ECU does it easily - and not so easily on an oil pressure switch.

BTW - did a Vega have FI?

[cayuse60]

The same switch would have to power it on for starting.. which is where the ECU does it easily - and not so easily on an oil pressure switch.

BTW - did a Vega have FI?

No...electric fuel pump:thumb

[jdiaz]

Does this ignition module have thermal grease underneath that needs to be renewed periodically? I've never touched mine in 18 years.....wondering if I should take it apart.

[Kayseventyfive]

The same switch would have to power it on for starting.. which is where the ECU does it easily - and not so easily on an oil pressure switch.



The starter circuit could energize the pump so the pump ran during cranking. Or you could use either a bypass switch or a time delay LC or 555 circuit. I have seen both on industrial engines which must shut down with low oil pressure. They use a Hobbes switch. I just thought throwing Vega into the mix would be interesting. Boats use this, too. I think Mercury sells the switch. A bypass push button switch would make a nifty anti-theft measure. :)

[breyfogle]

Does this ignition module have thermal grease underneath that needs to be renewed periodically? I've never touched mine in 18 years.....wondering if I should take it apart.

Nope, it just bolts to two rubber isolators (sort of like the battery tray isolators) with no heatsink other than its own surface area.

I did take the failed IM apart just to look inside a $900 piece of electronic wizardry. It is not a monolythic solidstate device and it is not potted in anyway. Inside, it is just a rather conventional circuit board with one microprocessor chip and a lot of good old fashioned discrete resistors, coils and capacitors. I suspect that the relatively high heat load in the area underneath the fuel tank might eventually do bad things to the electrolytic capacitors.

[deilenberger]

Nope, it just bolts to two rubber isolators (sort of like the battery tray isolators) with no heatsink other than its own surface area.

I did take the failed IM apart just to look inside a $900 piece of electronic wizardry. It is not a monolythic solidstate device and it is not potted in anyway. Inside, it is just a rather conventional circuit board with one microprocessor chip and a lot of good old fashioned discrete resistors, coils and capacitors. I suspect that the relatively high heat load in the area underneath the fuel tank might eventually do bad things to the electrolytic capacitors.Actually - the failure rate on these is so low that I doubt if the used price is much at all.. and I'd certainly never pay $900 for one (last one I bought for my "spare parts" collection for a K bike cost me $30 used..)

The early ones on K100's in '83-84 in Europe did have a bad habit of failing. It turned out they had trapped moisture in them causing them to go bad. BMW ended up replacing all of those - and getting a better quality one from the vendor. Yours is the very first I've heard of failing - and that's with about 12 years of helping people with their K bikes.

I guess there always has to be a first..

[breyfogle]

Actually - the failure rate on these is so low ...I guess there always has to be a first..

A first time I can understand, but what are the odds for having two fail on the same bike ? BTW, at $30 a copy, I'd buy a couple of spares. Even BBY wants $170+

I fairness, the original IM lasted about 12 years/90000 miles. When it failed, it was replaced by a used IM which was likely a similar age but unknown mileage. It lasted an additional 6 years/30000 miles. The latest IM is probably close to 20 years old and most likely will not last as long as either of the first two.

What concerns me is the "single point of failure" nature of the IM. I've been lucky in that both failures were related to the fuel pump control. There is a work-around for this that allowed me to get home. However, the primary purpose of the IM is to amplify and digitize the HES signal. (I'm guessing that it also applies the ignition advance as well.) If any part of that function fails, there is no "limp-home" mode.

[jdiaz]

Is this the part you replaced? EuroMotoElectrics has this thing listed as an ignition control module for $79. I recognize the connector but not where it goes.

http://63.135.101.225/database/mcinventory/Images/111_Pic.jpg

[breyfogle]

That part is way to modern for a K75.

A classic K-bike IM looks like this....

9455

[kennyD]

okay me and a buddy worked on my '95 K 75 for about three hours.
Here is where we are at and need some advice.

Fuel pump spins when power applied. So from pigtail to tank appears to be operating fine.

Bike turns over fine.

We do not have power on the green wire at the pigtail connection under the tank. We believe we should. Swapping out the two blue relays it appears that these are working properly.

Guessing that it is the large black fuel relay???

Any suggestions on where to go next?

Ken

[cjack]

okay me and a buddy worked on my '95 K 75 for about three hours.
Here is where we are at and need some advice.

Fuel pump spins when power applied. So from pigtail to tank appears to be operating fine.

Bike turns over fine.

We do not have power on the green wire at the pigtail connection under the tank. We believe we should. Swapping out the two blue relays it appears that these are working properly.

Guessing that it is the large black fuel relay???

Any suggestions on where to go next?

Ken

Could you be more specific about the green wire? Solid green wires are switched ignition power. They should be hot all the time from the ignition switch being on.

[breyfogle]

What I did when I got to the point you are now, was to remove the fuel pump relay and connect one test lead from an Ohm meter to the female side of the control input connector from the Ignition Module and the other test lead to a frame ground. You should have infinite resistance. With the ignition ON, spin the starter and the resistance should drop to zero as long as the starter is spinning the crank. If the resistance stays infinite, repeat the same test at the OM, pin #7.

[deilenberger]

We do not have power on the green wire at the pigtail connection under the tank. We believe we should. Swapping out the two blue relays it appears that these are working properly.

Guessing that it is the large black fuel relay???

Any suggestions on where to go next?

KenJust a note for future reference - the two BLUE relays are ABS relays and have nothing whatsoever to do with the bike starting. ALL blue connectors and components on the K bikes are ABS related. BMW was sorta clever that way.

And the green wire under the tank goes to (not having a diagram handy)?

[kennyD]

My bike does not have ABS so I guess BMW was not that smart if mine are blue.
Replacement relays are orange so perhaps they changed colors to be smart that way.

[deilenberger]

My bike does not have ABS so I guess BMW was not that smart if mine are blue.
Replacement relays are orange so perhaps they changed colors to be smart that way.Could it be the blue ones aren't originals?

[BCHAN]

(For anyone in a similar situation, a short legnth, 12 inches or so, of wire from the battery + terminal on the left to either side to fuse number 6 will bypass the fuel pump relay and apply 12 volts directly to the fuel pump).



Could some one clarify for me just which of the seven (7) vertically aligned fuses is the "number 6" fuse?

Is it number six from the top?

Or is it number six from the bottom?

Many thanks!

BC

[breyfogle]

Fuse number one is the upper most fuse -> seven, the bottom.

Typical wiring diagrams, such as in the owners manual, *draw* the fuses out of order to make the diagram easier to read but number each fuse position 1 - 7.

[BuddingGeezer]

Fuse number 6 receives it's power from the fuel injection relay. If you turn the igniton on this fuse is not hot until the starter button is pushed, then the fuel injection relay is energized, thus sending power to the fuse number 6 (second from the bottom).

Then the #6 fuse sends power to the fuel level sensor in the tank that powers the fuel pump.

Only when the starter buton is pushed will the green or green/white wire be hot.

This ran me crazy thinking the fuse is hot with the ignition on. Finally after tracing wires and restudying the wiring diagram I learned my error.

Germans do it different.

Ralph Sims

[breyfogle]

....Fuse number 6 receives it's power from the fuel injection relay. If you turn the igniton on this fuse is not hot until the starter button is pushed, then the fuel injection relay is energized, thus sending power to the fuse number 6 ....Ralph Sims

True enough but as I mentioned in my original post, if you every need to test the fuel pump or bypass the fuel pump relay, applying battery voltage to fuse 6 is easy and will bypass most of the electrical harness and route battery voltage to the fuel tank pigtail connector. If that's OK, the fuel pump should spin.

[BCHAN]

Fuse number one is the upper most fuse -> seven, the bottom.

Typical wiring diagrams, such as in the owners manual, *draw* the fuses out of order to make the diagram easier to read but number each fuse position 1 - 7.

Thanks a bunch for confirming fuse 6 location. I really appreciate your posting this thread and everyone elses comments/input here.

I did the direct power to the fuel pump via fuse 6--- fuel pump was heard whizzing in the tank. The starter then can be turned over just fine but bike still does not fire up. Is it possible that the fuel pump is pumping but just not enough to make things work?

Or is it more likely that I am just not getting any fire from the plugs. Does this still sound an ignition module problem?

I know this is not great detail...but appreciate any thoughts anyone might have.

Many thanks!

BC

[BuddingGeezer]

I recently bought a 1987 K75, that the PO said he rode, killed the bike and it never started again. I pulled my hair out and wore my fingers out typing on this forum diagnoising the problem.

John Diaz had the solution. Check the mass air flow sensor. Mine was not in the boot. I opened the flap with my finger, hit the starter, ran great.

This may not be your problem, but?????????????????

Ralph Sims

[cjack]

I recently bought a 1987 K75, that the PO said he rode, killed the bike and it never started again. I pulled my hair out and wore my fingers out typing on this forum diagnoising the problem.

John Diaz had the solution. Check the mass air flow sensor. Mine was not in the boot. I opened the flap with my finger, hit the starter, ran great.

This may not be your problem, but?????????????????

Ralph Sims

If that happens, the bike will start and idle. When you twist the grip, it dies.

[BuddingGeezer]

True, t5he bike would start and idle, die when throttle was opened. Allthough, the bike would not start untill I installed a new set of Bosh sparkplugs. It would not run on the new set of NGKs the PO had installed.

I do not know how to use the quote feature.

Ralph Sims

[reimerdavid]

Riding home from work yesterday afternoon, I stopped at a gas station near home. Filled the tank, paid for the gas, and started (or tried to) the bike to leave for home. Hitting the starter button produced lots of starter noise but absolutely no indication of any hint of ignition what-so-ever. DARN !! K-bikes are supposed to almost unbreakable and mine had been running great right up until I shut it off for gas.

Anyway, it did not take to long to determine that the fuel pump was not running. If the fuel pump failed, the bike had to towed home. If there was an electrical fault maybe I could jury-rig something to get home. After studying the wiring diagram, I figured that I could easily hot wire the fuel pump directly off the battery. (For anyone in a similar situation, a short legnth, 12 inches or so, of wire from the battery + terminal on the left to either side to fuse number 6 will bypass the fuel pump relay and apply 12 volts directly to the fuel pump).

Tried it and the pump spun fine and the bike started as easily as K75's are supposed to start ! Got home OK but I have not yet tried to determine why the fuel pump stopped receiving volts. Could be a simple wire or plug related fault. Could be the HES but I doubt it since the bike ran fine before and after. Could be the ignition module or the computer, hope not ($$$$+ hard to diagnose).

Anyone want to suggest where I might begin tracing this problem down?

Same thing happened to my bike years ago. It was the Relay that controls the Fuel pump, can't remember which one however. Good Luck, Dave

[ziegelreiter]

Now that's just plain cruel:brow

Not that I don't enjoy spending less time laying on the garage floor ever since I swapped the '92 K75S for a R1150RT-P... :bolt

How do you like the RT-P? Is a state bike or city?

[barryg]

I went thru a period with my 87 K100 when I would be riding along and it would just die,then later start running, just drive me crazy. Every test would show good when running, obviously. I was running the bike checking out different things, I just happen to jiggle the wires from the sending unit coming out from under the tank. I could kill the engine moving those wires around, problem solved. New unit installed no more problem. Could be your problem.