'85 K100RS Bad fuel pump or fuel pump relay?

[117336]

Hi Lee,

So the pump is in with the new strainer, tank cleaned and just to be sure I did the key on and starter pushed quick test to hear her running. AOK. Put in some fuel crossed my fingers and ... same **** errrr. Starter oak, fuel check, clean air filter check, Got to check plugs next and maybe if there's a relay to check I will do that as well. Going to read my Haynes by the window and dream of cruising in the countryside. Could that have been the sound I heard when it quit? Maybe a relay popped or I need new plugs and wires?

[98lee]

Hi Lee,

So the pump is in with the new strainer, tank cleaned and just to be sure I did the key on and starter pushed quick test to hear her running. AOK. Put in some fuel crossed my fingers and ... same **** errrr. Starter oak, fuel check, clean air filter check, Got to check plugs next and maybe if there's a relay to check I will do that as well. Going to read my Haynes by the window and dream of cruising in the countryside. Could that have been the sound I heard when it quit? Maybe a relay popped or I need new plugs and wires?

I'm not really clear what you symptoms are.

Does the bike crank?

Does the pump run?

Do you have spark? You can get a cheap in-line spark tester at HarborFreight or many car parts stores.

What is the fuel pressure? (tee in a gauge at the fuel rail).

[117336]

Hi Lee,

I need to get some tools and wonder if this will do the trick>
http://www.harborfreight.com/automot...ter-92699.html
It says that it doesn't fit a bosch fuel injector but if I attach it to the hose before the injector it will test the fuel pump pressure and that's what I need I think.
and this:
http://www.harborfreight.com/automot...ker-69023.html
Will it fit?
Thanks in advance for your patience and help.
S

[98lee]

Hi Lee,

I need to get some tools and wonder if this will do the trick>
http://www.harborfreight.com/automot...ter-92699.html
It says that it doesn't fit a bosch fuel injector but if I attach it to the hose before the injector it will test the fuel pump pressure and that's what I need I think.
and this:
http://www.harborfreight.com/automot...ker-69023.html
Will it fit?
Thanks in advance for your patience and help.
S

Both those SHOULD work just fine.

When taking fuel pressure measurements, it's easier to tee into the hose at the REAR of the fuel rail. That's the hose that goes to the fuel pressure regulator.


If your bike is cranking and the fuel pump is running, it's possible that the spark plugs are fouled. Clean, Dry, and regap.

[117336]

Hi Lee,

Lapse in time due to necessary work schedule... Anyway got the tools and tested the spark to find 1 of the 4 not firing. Could be the wire or the coil, yes? Would that be enough to make it not start? Should I change the wires and test #1 again to rule out the Coils or is there a way to gap test the coils or try and check the wire? (I know your thinking... rookie)
Have not checked the pump pressure yet but know when I was testing it in the bucket it was pumping. Will test it this week.

[98lee]

Unless I'm mistaken, on a K100, each coil fires TWO plugs. Since at least one plug is firing on each coil, both coils are working.

I would pull the plug that is not firing and one of the plugs from the coil that is firing both. Check the gap and clean and dry them. Now put them in the opposite cylinders. If the non fire moves with the plug and both plugs fire with the coil that previously only fired one, you have a bad plug. Or they are so fouled that they won't fire (my guess).

If the same cylinder does not fire, MIGHT be a bad wire. Try swaping wires (move both ends of a wire that is working to the coil terminal and plug that is not working and take the wire that is not working to a position that is working). Does the problem move with the wire? Make sure the plugs are connected to the correct coil terminals.

Basically, does the problem move with the plug or the wire or does it stay with the coil/cylinder?

As far as the rookie comment, every expert/pro started as a rookie!

[117336]

Hi Lee,

Sorry for the lapse. Went riding on the gs and had no time lately between work and chores.

So I did what you suggested and tested the wires and plugs by swapping a good one for the problem child. I was able to isolate the #1 wire as the culprit and found a replacement for the #1 plug wire and swapped it out. Started right up. So plugs are fine, wires too and the fuel pump is doing its thing. Cracked the throttle in neutral and it revved up and back to idle. Stopped it. Started it and all seemed ok. Put all the covers back on and took a ride around the block. Then stopped and restarted. Went for a longer ride and stopped to find the same problem happening. Cranking, pumping but not starting. Did an inspection on the bike and the only thing wrong was the rear brake light switch was not firing the rear brake light. Front brake switch works fine so the bulb is good. Could this be related?
S

[98lee]

Brake light switch should not be related.


Use your spark tester. Are all 4 plugs firing? Are the plugs gapped correctly?

Use your fuel pressure tester. What is the fuel pressure when TEE'd into the line at the rear of the fuel rail?

[117336]

Hi Lee,

I am back like an addiction. Pressure tested the fuel pump and all seems good. changed the fuel filter just in case it was clogged... it wasn't. Plugs and wires tested and cleaned and gapped. Changed the brake light switch to a known working one and still not working. Will worry about that one later. Attached is a pic and video. May have to truck it to the dealer soon as I am running out of options. In speaking to the parts guy at BMW Manhattan, he said it may be the mototronic? After the bike reaches warm up temp it dies. Will attach a video with sound. What a puzzle.
here is a link to a video of the problem:
schedivypictures.com/k100/k100.mov

[98lee]

The two things that I noted on the video was that you are very low on fuel in the tank and the the bike is idling very low.

Check the crankcase vent hose for ANY cracks. Check the throttle body vacuum caps for any cracks. Make sure the vacuum hose on #4 throttle body is in place. The way it stalled, combined with the low idle, I'm thinking large vacuum leak. That also goes along with your test ride that went well until you stopped.

The fuel pressure is low. Should be 36-38, but that MIGHT be gauge variation.

[Zagando]

117336; Nice looking bike you have there; hope you can get it sorted easily. I am partial to stripped/polished tanks as that's what I did with mine (much to Lee's chagrin as he loves Dakar Yellow for some strange reason).

Have you considered replacing the roundels on the sides of the tank? They're $30 a pop at the dealer's but really put a nice finishing touch on your K.

Now back to the thread at hand...

Aloha from Albuquerque where we just had our first freeze last night (took out my zucchini crop) Jeff

[Roc-Roc]

Hey 117336

I had an 85 K100RS, it had over 100k miles when its fuel pump die. Before it died it would do the same thing like yours intermittent for over 2200 miles(between miles 150 and 1900 it ran great no porblems). I change the fuel filter twice, the strainer, check connections to the computer, and check spark plugs/wires. I had the pressure check by a dealer he said it was ok and then it died 300 miles from that dealer. When it dies it will blow the fuel pump fuse until then it will keep being intermittent. I think its the fuel pump.

By the way the fuel pump was replace at 110k miles, that bike was sold with that replacement fuel pump with 230k miles.

[Beemer01]

And as an old 85 KRS owner - I have to ask....have you checked that under tank connector? Known problem design and by 2012 this part is often loosened up enough that the male pin, female sleeve connections are just loose. When the bike next stops, reach under the tank, jiggle this connector and try and restart.

If this is the problem - simply reseating the connector will not permanently fix the problem. Search the forum to see what others have done to replace this plug.

[117336]

Hey Zagando: You and Berlina were the inspiration for stripping the tank. I followed your thread and decided to do it. Came out a bit rougher than yours but not bad for a first. I have the roundels but have not put them on yet.

Roc-Roc: I hope its not the pump. I am pretty sure it was replaced after sitting for years in a garage before I bought her. I heard it may be the fuel injector computer? May have to bring the bike in and have the pros check it out.

Beemer01: If you mean the round power plug under the front left, I jiggled the crap out of it and cleaned the contacts and prayed to it but no go so far.

98Lee: I'll check for vacuum leaks and cracked hoses next... after the N'or Easter.

Thanks for all your input btw! I am thinking of calling on someone in the area with the same bike to allow me to swap computers and see if that fixes it.

[Zagando]

Hey Zagando: You and Berlina were the inspiration for stripping the tank. I followed your thread and decided to do it. Came out a bit rougher than yours but not bad for a first. I have the roundels but have not put them on yet.

Cool! Glad to know that my long and drawn-out thread was of help and inspiration to you. Getting a good polish is much harder than it would seem.
The best advice I can give is to sand with 1000 grit, then clean throughly and sand with 1500, clean, 2000, clean and go all the way to 2500 grit before getting out the Blackfire or Mother's or whatever polishing compound you use.

It's a ton of work but once you get a really fine polish you'll be proud.

Upkeep is also another chore that needs to be done somewhat regularly and I fell down in that dept. before we left Hawaii. Corrosion was beginning to be really noticeable on the fork brace and rear rack but the tank was only beginning to get hazy earlier this year.

Now that we're in such a dry climate I'm really motivated to renew the polish as well as the runnings of Berlina---I may have to revitalize my DIY renovation thread at the rate I'm going, too! (new battery, fuel lines, filter, pressure regulator, vacuum hoses, fork seals, boots, valve adjustment, fan motor, etc.)

I bet you'll get loads of compliments on your K once you get her going around the Big Apple and I wish you the best of luck on fixing the fuel problem. Although the squealing noise that I thought was something to do with the pump or regulator it turned out to be something entirely different. I don't regret my actions, though as now I have that much more practical knowledge in regards to the fuel system ( and I learned the trick in getting that snug airbox in and out from underneath the frame, too).

Hope the coming storm doesn't do you any more harm and that your K will be running like it should soon.

Regards,

Jeff