Author Topic: 1992 BMW K75S ABS Running Rough & Rich  (Read 947 times)

Offline ExpatAussieBrick

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1992 BMW K75S ABS Running Rough & Rich
« on: June 27, 2019, 05:29:47 PM »
Hey guys,

So i'm a bit bloody stumped on what is happening with my bike. It's a 92 K75S and it's been running poorly the past few weeks after I had it serviced at BMW of Manhattan. It was running great after the service until about 30min after I left the dealership it suddenly refused to rev above 3000rpm and the engine slowly bogged down and died, almost causing me to be squashed like a bug by heavy traffic on the Queensborough bridge.

After I managed to coast down the bridge and get it started again it ran fine for a little while then back to stalling again. I decided it might be water in the tank or a bad fuel filter I drained the tank and replaced the fuel filter still nothing changed. I checked the plugs and they looked a little rich.

So I took it back to the dealership and they diagnosed it as running rich under load with a vacuum leak at the air intake manifold and the injectors. They replaced the rubber hoses under there and the Injector O rings but was still running roughly. They then installed a used Mass Air Flow Sensor thinking that would fix the problem it didn't. Frustrated I took it back from them not wanting to burn anymore cash.

They suggested that I try installing a new Hall Effects Sensor.

Does anyone have any other ideas about what it could be? I'm thinking of pulling the injectors myself and having a look at the spray pattern and also try a new HES. But I don't really wanna just keep throwing parts at it and hoping for the best without a clear diagnosis.

It's a shame it's my first BMW and it was a fantastic bike when it was running well only had it for 6 months. I'm from Australia but living in NYC and the bike is my only set of wheels to get me out of town this summer so I really wanna try getting it running again.

 :beatdeadhorse:






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  • New York
  • 1992 BMW K75S ABS

Offline natalena

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #1 on: June 27, 2019, 06:12:25 PM »
Sorry to hear your brick is turning into a wonkasaurus. Pics of the plugs will help. Has the fuel lines been replaced, the fuel pressure regulator? Sometimes the fuel lines get crimped under the tank and cause intermittent starvation, then the bike runs fine again, then acts up again. Have patience, and others will chime in that know waaaaay more then I.
  • East of Joshua Tree
  • 1987 K75s #0919
On Holy Quest seeking Techron equivalent for splines.

Offline johnny

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #2 on: June 27, 2019, 06:54:30 PM »
greetings...

poast up some photos... wanna see if its been bastardized...

im calling fore pin...  do all this and ping back here...

http://www.motobrick.com/index.php/topic,11033.0.html

j o
  • :johnny i parks my 96 eleven hundert rs motobrick in dodge county cheezconsin  :johnny

Offline Laitch

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #3 on: June 27, 2019, 07:32:55 PM »
BMW service centers have all the diagnostic tools that anyone could want. The elements of efficient and predictable operation are the same in these motos as any other—fuel, air and spark. Staff trained in electronic diagnosis should be able to identify the problem, not guess at it. Throwing parts into a malfunctioning moto is what greenhorns do. You did right by getting away from them and not continuing to throw parts at it yourself.

What is the service they performed on the moto exactly? It seems as though it was running alright before you went there. Is that correct? If it is, I don't believe it's coincidental that the moto started running unpredictably after they handled it.
  • Along the Ridley in Vermont.
  • 1995 K75T 72,000 miles
I wept because I had no radials until I met a man who had no splines.
http://www.motobrick.com/index.php/topic,296.msg53303.html#msg53303

Offline Scott_

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #4 on: June 27, 2019, 10:17:25 PM »
Sounds like another example of current shop staff not having any training or experience with 25+ year old bike.  If a computer can't tell them what's wrong, they don't know how to figure it out. Unfortunately most everything is going this direction.

They may be able to say that there are 'parts available for all bikes new and old'..... to bad they can't fix old bikes.

I'll get down off my soap box now... rant off.
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Offline Martin

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #5 on: June 27, 2019, 11:05:12 PM »
As per Nat the fuel return line between the FPR and the tank can crimp over, this will cause the bike to run rich and rough. The OEM return line has the bends molded in whereas a replacement straight piece of fuel line doesn't . If fitted with a straight piece of line crimping can occur especially on some of the cheaper hose that is around. The crimp can be hard to detect as when you slide the tank back it will sometimes uncrimp, feel and bend the last couple of inches of the line to see if it has delaminated or gone soft. High temperature days make the line more prone to crimping. If it has crimped either replace the line with an OEM line or fit a Unicoil over the last piece of line. Fitting an extra hose clamp below the Unicoil will prevent it from sliding down.
Regards Martin.
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  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline riots100

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #6 on: June 27, 2019, 11:54:22 PM »
You mentioned that you drained the tank and replaced the fuel filter, did you pull the fuel pump and look for accumulated sediment and crud clogging up the fuel strainer on the fuel pump?  This would starve the fuel pump and thus the engine.  After letting it sit a while, the sediment will drop off the strainer and then it would seem to work just fine until the sediment would get stirred up and clog the system again.  This cycle runs in a tighter loop with less fuel in the tank.

I had a similar experience to yours on two motobricks.  Removing and throughly cleaning the tank solved the issue completely.  On one machine I had to replace the fuel strainer.

I agree with the others in that dealerships and other generalists aren't going to know much about these bikes.  The bikes are too old and they have other fish to fry.  They will just through new parts at the machine until the problem is solved.
  • Los Angeles, CA
  • 1992 K75, 2007 K1200GT, 1991 K100RS
----
BDJ

Offline The Mighty Gryphon

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #7 on: June 28, 2019, 12:36:09 PM »
Welcome, and condolences on your situation.  You definitely made the right decision to get away from the dealer.  Any mechanic who equates an intake air leak with rich running should be avoided. 

As was mentioned above, a picture of the spark plugs would be very handy.  That will tell conclusively whether the bike is running rich or lean.   There are several things I would have you check, but won't make any suggestions until I see what the plugs look like because the troubleshooting paths are different.
  • In my garage in Marilla, NY
  • '94 K75RT Mystic Red, '91K100RS White/Blue
Current:
'94 K75RT "Ilsa, She Wolf of the SS"
'91 K100RS "Moby Brick Too

Offline Scott

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #8 on: June 28, 2019, 12:57:06 PM »
Given it ran good until it warmed up and appears to be running rich, perhaps there is a sensor that thinks the bike is cold, calling for a rich, cold condition mixture that is unnecessary. Just thinking out loud, but seems like a logical area to explore.  Hard to believe a BMW service facility can't figure it out.   Good hunting. 
  • SoCal
  • bmw R100r, bmw k75, hondapotamus G/W, XT 500 enduro

Offline ExpatAussieBrick

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #9 on: June 28, 2019, 02:05:25 PM »
Thanks for all the suggestions guys! Great community never had this support on the previous two bikes I owned.

 I am going to go through those basic 4 pin connectors and clean them up this sunday and post back.

In regards to the tank I've given it a good wipe down its very clean in there no sediment I can see all the rubber hoses in the tank are in good condition as far as I can tell. But no harm pulling the pump out to check I guess. Will check hoses to the FPR as well I am getting decent flow return to the tank when the engine is on but not sure if that means anything. The pump does have quite a loud hiss but that could be normal. The dealer told me the pump was fine they said it either fails and leaves you stranded or doesn't it's not intermittent they said they checked fuel pressure and it was in spec.

Now in terms of what had been has been done to the bike at the dealer they replaced the front and rear break pads they blead and refilled the break fluid they mounted two new lasertec tyres. They changed the engine oil and replaced the filter and they changed the oil in the final drive and transmission. As part of an all inclusive deal they were doing on annual service.

After all that the bike started running rough shortly after I took it back.

I bought this bike for very little $1500 on Craigslist its not been taken the best care of by the PO but it was at least garaged and came with a new battery. It didn't come with a service history so I took a risk but I thought it was still a lot of bike for that money even if I did have to replace a bunch of things.

Anyway will have a go working on it on Sunday and report back with photos.
Cheers




  • New York
  • 1992 BMW K75S ABS

Offline The Mighty Gryphon

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #10 on: June 28, 2019, 04:47:14 PM »
Please take the bike out and run it until it starts to misbehave, bring it home and take photos of the spark plugs.  The mixture is off, but without a plug reading there is no way to tell for sure whether it's rich or lean.  Depending on which way it's off, it will guide the troubleshooting sequence.  My money is on the engine temperature sensor, but without a plug reading I'm holding off on saying what I think it is.

It's good to learn how to do your own work on the bike.  Except for the tires you could have done the rest of the work the dealer did with a few dollars in tools and maybe $100 for parts and supplies.   The really good news is that the inmates here can talk you through almost any job on your bike.
  • In my garage in Marilla, NY
  • '94 K75RT Mystic Red, '91K100RS White/Blue
Current:
'94 K75RT "Ilsa, She Wolf of the SS"
'91 K100RS "Moby Brick Too

Offline ExpatAussieBrick

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #11 on: July 01, 2019, 09:22:34 PM »
Hi Guys,

Update on the bike. So this afternoon I cleaned up the battery contacts and the 4 pin connector underneath the tank with deoxit and an old toothbrush. Also noticed that the big hose containing the wiring for the ECU fuel injection computer was pretty kinked around so straightened it out as best I could.

Here are some pics of the 4 pin.

4 pin male
https://www.dropbox.com/home/Bike%204%20PIN?preview=IMG_4051.JPG

4 pin female
https://www.dropbox.com/home/Bike%204%20PIN?preview=IMG_4052.JPG

I then took it for a 45min ride expecting it to act up at any time. On the contrary, it ran really well as good as it was before the incident maybe better. No bogging no stalling just smooth and powerful linear power with very little flat spots except maybe a little choppy in first when on an off the throttle which I believe is normal for the bike. It being NYC I didn't manage to get it flat out but I did take it to a few empty stretches of road in Brooklyn to really wring its neck and it responded well.

Really is night and day when I drove it back from the mechanic a few days ago it died 3-4 times on the short 30min ride home.

Is it really possible that it could be fixed from something as simple as cleaning the battery contacts and 4 pin connector?

If so I'm pretty over the moon!

I am planning to take it on a long ride out to Rockaway beach tomorrow so will keep you posted on how it goes.

After I got home I pulled the plugs to take a look. Here are some pics.

Plug 1
https://www.dropbox.com/home/Plugs?preview=IMG_4058.JPG

Plug 3
https://www.dropbox.com/home/Plugs?preview=IMG_4061.JPG

Plug 2
https://www.dropbox.com/home/Plugs?preview=IMG_4065.JPG

Here are some pics of my old blue bimmer and my not so ideal work-space on the streets of Brooklyn.

https://www.dropbox.com/home/Bike%20Pics%20Outside?preview=IMG_4054.JPG

https://www.dropbox.com/home/Bike%20Pics%20Outside?preview=IMG_4053.JPG





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  • New York
  • 1992 BMW K75S ABS

Offline The Mighty Gryphon

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #12 on: July 01, 2019, 10:01:33 PM »
Congratulations on the fix!

I was hoping to see the plugs, but I need a drop box account.  I'd rather not.
  • In my garage in Marilla, NY
  • '94 K75RT Mystic Red, '91K100RS White/Blue
Current:
'94 K75RT "Ilsa, She Wolf of the SS"
'91 K100RS "Moby Brick Too

Offline ExpatAussieBrick

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #13 on: July 01, 2019, 10:06:18 PM »
Here we go.

Will upload these spark plug pictures directly as an attachment.

  • New York
  • 1992 BMW K75S ABS

Offline The Mighty Gryphon

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #14 on: July 01, 2019, 10:16:35 PM »
Your engine is not running rich.  The plugs look good if not on the very slightly lean side.  I would say your mixture is pretty good.
  • In my garage in Marilla, NY
  • '94 K75RT Mystic Red, '91K100RS White/Blue
Current:
'94 K75RT "Ilsa, She Wolf of the SS"
'91 K100RS "Moby Brick Too

Offline ExpatAussieBrick

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #15 on: July 01, 2019, 10:22:17 PM »
Excellent that's what I thought looking at them as well.

Weird that it was diagnosed at the mechanic as running rich makes no sense.

Hopefully this means that the fault was electrical which does seem to make sense as it's intermittent and that going through and methodically cleaning the grounds and connectors will ward off future issues.

Will post back after a good ride tomorrow to confirm if the issue is resolved.



  • New York
  • 1992 BMW K75S ABS

Offline Laitch

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #16 on: July 01, 2019, 11:24:30 PM »
If your moto's rear brake cylinder reservoir hangs on the frame behind the battery cover, it's possible the tech doing the brake work decoupled the four-pin connector to have easier access to filling the reservoir; afterwards, it wasn't reconnected firmly or debris infiltrated the connection and interfered with it.

How about posting some photos of your machine?
  • Along the Ridley in Vermont.
  • 1995 K75T 72,000 miles
I wept because I had no radials until I met a man who had no splines.
http://www.motobrick.com/index.php/topic,296.msg53303.html#msg53303

Offline ExpatAussieBrick

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #17 on: July 03, 2019, 01:58:58 PM »
Hey guys,

Good news! took the bike for half day ride yesterday all over town. Took it up to speed on the BQE & Belt Parkway it's running great back to it's old self.

Can't believe the amount of time I wasted should have come here straight away. At least I know where to go in the future.

So as was stated previously what probably happened is the tech who refilled the brake fluid reservoir when the brakes were flushed did not install the 4 pin connector properly back together or got lint stuck in the connection which the deoxit fixed. The deoxit also fixed my flaky speedo that stuff is magic!

Couldn't be happier i'm planning on doing a long ride down south with my mate and his triumph. So will make sure to post a ride report and some pics we are doing the outer banks and then over the great smoky mountains to West Virginia and back to NYC is the plan.

Next thing to do is replace the grips 'one has a hole where the PO dropped the bike' and to do a spline lube as it's got 35000 miles and god knows when it was last done.

Thanks so much for all the help and here are some pics of the bike.


  • New York
  • 1992 BMW K75S ABS

Offline ExpatAussieBrick

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #18 on: July 03, 2019, 02:01:45 PM »
Pics
  • New York
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Offline ExpatAussieBrick

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #19 on: July 03, 2019, 02:03:18 PM »
Pics
  • New York
  • 1992 BMW K75S ABS

Offline SDCR john

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #20 on: July 03, 2019, 02:07:13 PM »
Very nice! Looks good in that blue shade.

If your coming through southeast Pa, the area around Philly, drop me a pm. I can show you some nice local roads, and good places to eat.
1994 BMW K75S Dakar Yellow #0154446
1983 Moto Guzzi 850 Le Mans
2000 BMW R1100 RS
Bucks County Pa.

Offline natalena

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #21 on: July 03, 2019, 02:18:27 PM »
Is it really possible that it could be fixed from something as simple as cleaning the battery contacts and 4 pin connector?
Yes, and now you have your own "4-pin" story to relate at gatherings :)
It's still worth some maintenance time for the fuel delivery system, and don't forget that pesky "Z" tube behind the throttle body sensor.

Glad to hear the world is back in balance for you. FWIW, Mid-Atlantic Meet-up II is coming up on July 20th (Waldorf, MD) if your in the area.
  • East of Joshua Tree
  • 1987 K75s #0919
On Holy Quest seeking Techron equivalent for splines.

Offline The Mighty Gryphon

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #22 on: July 03, 2019, 03:39:47 PM »
Very nice looking bike.  That's a nice shade of blue.  There are many who think the K75S is the nicest model in the classic K bike lineage.  Judging from the photos, yours certainly is one of the better examples.
  • In my garage in Marilla, NY
  • '94 K75RT Mystic Red, '91K100RS White/Blue
Current:
'94 K75RT "Ilsa, She Wolf of the SS"
'91 K100RS "Moby Brick Too

Offline caveman

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #23 on: July 04, 2019, 08:12:09 AM »
Very nice looking bike.  That's a nice shade of blue.  There are many who think the K75S is the nicest model in the classic K bike lineage.  Judging from the photos, yours certainly is one of the better examples.

you can guess where I stand on that statement!

 ExpatAussieBrick,
Have fun on the trip and please post a report. The Smokies and Appalachian mountains are so far my favorite place to ride. Some of the popular roads (129 Tenn. the dragon, 209 N.C. the rattler, 16 Va. the back of the dragon, and so on) can be real zoo on weekends so you may want to plan to hit them mid week or early or late in the day. Also I see you have Metzler Lazer Tec tires on your bike IMO, I do not like them and have had poor performance from them. On my 75s they had very poor grip on wet roads and have worn out rear tires in less than 2,000 miles. FWIW I've had good luck with Avon M28s.

Sorry, Just my 2 cents that you didn't ask for.

  • Kennerdell, PA.
  • 87 K100RT, 88 K100LT

Offline natalena

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Re: 1992 BMW K75S ABS Running Rough & Rich
« Reply #24 on: July 04, 2019, 03:29:00 PM »
we are doing the outer banks and then over the great smoky mountains to West Virginia and back to NYC is the plan.

I grew up in Afton, VA. and the section of the Blue Ridge Parkway (BRP) between Humpback Rocks and Ferrum (Roanoke) is pure Nirvana (expect 3-3.5 hrs) on a motorcycle. If you're riding the southern Smokey's it's worth the ride time to go up the BRP, and cut west at Waynesboro/Staunton to get to WV. *my first moving violation for leaning, dragging peg, and speeding over the double yellow was on the BRP in the 70's ... on an awesome RD400. :)
  • East of Joshua Tree
  • 1987 K75s #0919
On Holy Quest seeking Techron equivalent for splines.

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