92 K75 o2 sensor

[tricyclerob]

Help, I think I must be losing it. Bought a K75Rt, w/37,000. The prev. owner mush have been an electrical engineer. It appears he had a device on the bike for adjusting the fuel delivery. He took the device off , but left numerous wires and connections behind. I have just about everything figured out but the wire for the O2 sensor. I have searched my Clymer manuel .,as well as the wiring diag's but cannot find any mention of the sensor or the wire. Where does the stock o2 sensor wire attach??? I just sold my 92 K75s [sm yr., sm.color]to my neigh. and looked at that but did not see a sensor on that. Help!! :banghead

[soldemall]

Don't know what wires you are looking at that the PO added, but the bike has no oxygen sensor. It is fuel injected to be sure, but is an open loop circuit, just as cars had in the late '70s.

[tricyclerob]

maybe I'm not identifying the part correctly. It's what appears to be a sensor, screwed into the exhaust pipe at the collector, just in front of the muffler. Has one blue wire. It faces inward ,b ut I looked to det if it was something the po added, but it has a factory looking welded boss w/threads for it to screw into. Anyone Know what I'm looking at?????

[cjack]

maybe I'm not identifying the part correctly. It's what appears to be a sensor, screwed into the exhaust pipe at the collector, just in front of the muffler. Has one blue wire. It faces inward ,b ut I looked to det if it was something the po added, but it has a factory looking welded boss w/threads for it to screw into. Anyone Know what I'm looking at?????

That's not stock. There was nothing screwed into the exhaust on the K75.

[tricyclerob]

Well, I just looked at it again, and it's a very neat looking install. Sure looked factory. On my K75s, the worst "lean" condition I had was an occasional, popping out the exhaust on deceleration. Were some K75's that much worse than others? It did not seen worth all the effort the po went to. Am I correct in that I can just remove the sensor and screw a plug in? Would a brass plug present any problem? thx,rj

[Kayseventyfive]

Well, I just looked at it again, and it's a very neat looking install. Sure looked factory. On my K75s, the worst "lean" condition I had was an occasional, popping out the exhaust on deceleration. Were some K75's that much worse than others? It did not seen worth all the effort the po went to. Am I correct in that I can just remove the sensor and screw a plug in? Would a brass plug present any problem? thx,rj

Some people use an O2 sensor to read fuel mixture, either with a dedicated meter of a DVM. Go ahead and put in a brass plug. The popping on deceleration is perhaps indicative of a failed throttle position sensor that is supposed to shut off fuel delivery on closed throttle. It is part of the K75 experience.

[breyfogle]

....The popping on deceleration is perhaps indicative of a failed throttle position sensor that is supposed to shut off fuel delivery on closed throttle. It is part of the K75 experience....

The most common cause for "popping on deceleration" is a TPS that is not adjusted properly. Failure is unlikely. The TPS should be positioned (i.e. rotated) so that a distinct click can be heard just before the throttle is fully closed or just after the throttle begins to open after being fully closed.

[tricyclerob]

Thanks for everyones help. rj

[nh7robmw]

I have some popping and burbling upon deceleration with my '94 K75S. Where is the Throttle Position Sensor located and how do I go about adjusting it, please?

I'm guessing it is on the handlebars and is easy to do but I want to make sure before I jump in.

Thanks in advance (and hope you see this reply to an old thread).:clap

[Gilly]

YEAH we see it. IIRC it is at the very end of the throttle linkage, you'll see a wire going to it. Probably can find good instructions at the IBMWR site. I'll look and report back.
Gilly

[Gilly]

Hopefully Paul or Don will arrive soon so I don't lead you totally astray! But here is a link I found for ya:
http://www.ibmwr.org/ktech/backfire.shtml

Gilly

[PGlaves]

Hopefully Paul or Don will arrive soon so I don't lead you totally astray! But here is a link I found for ya:
http://www.ibmwr.org/ktech/backfire.shtml

Gilly

That link is old but still correct. Look for the square black box on the back end of the throttle body shaft. It is a 3 position switch. Normally off - on in one position at full throttle which signals wide open throttle and causing the mixture to be enrichened. And, closed throttle causing the ECU to shut off the injectors if the engine is over 2,000 rpm. You can test it with an ohm meter, or listen for the audible click as the switch closes at closed throttle. To adjust loosen the two little bolts and rotate the switch.

Other than the switch the two main causes of backfire are rider habits and exhaust leaks. By rider habits I mean rolling off the throttle almost but not quite all the way - thus not closing the switch, so it keeps pumping in fuel, some of which goes unburned into the exhaust, and then lights off with a bang when you get back on the throttle.

Exhaust leaks can draw in fresh air (oxygen) which can also cause unburned ruel rmnents to light off with a bang in the exhaust system.

[Gilly]

Paul, doesn't that "fuel over run" ie the act of shutting off the fuel with closed throttle yet rpm over 2000, have something to do with the popping/backfiring? That's what the dealer told me many years ago.
Thanks for the personal reply on my FD question, BTW.

Gilly

[nh7robmw]

Thanks Gilly and Paul; It's raining cats and dogs around here lately so I will check for the click next dry day we get. I'll try checking the switch with my multimeter, too.

I may also try to check for any header/exhaust leaking---maybe with some soapy water on the joint upon startup? The exhaust looks fine but the headers are discolored and mostly dark brown---perhaps the connection between them and the muffler will be suspect.

[Gilly]

You'd be looking for a black sooty stain. The pipes are stainless and yeah get this brownish or brassy tarnish to them from the heat, they typically don't turn the blue color that chrome does, not on the collector anyways.
If in doubt I have used soap before too, might want to spray that on first, then start it and so on.
If no luck, but you can still HEAR a leak, a couple foot section of heater hose placed to the ear can help locate/isolate noises.

Gilly

[deilenberger]

Other than the switch the two main causes of backfire are rider habits and exhaust leaks. By rider habits I mean rolling off the throttle almost but not quite all the way - thus not closing the switch, so it keeps pumping in fuel, some of which goes unburned into the exhaust, and then lights off with a bang when you get back on the throttle.

Exhaust leaks can draw in fresh air (oxygen) which can also cause unburned ruel rmnents to light off with a bang in the exhaust system.

This is particularly true at higher altitudes going downhill with partial throttle. My S loved to bang away horrendously riding in the upper mountains in WV.. people learned not to follow me too close on downhill sections. The extra rich mixture (due to altitude) along with partially open throttle (using it for engine braking) results in some very loud BANG!s - loud enough they startled me on occassion.

It's just part of the charm of a K75..

[nh7robmw]

Good tip on the heater hose, Gilly; I'll try it sometime.

[nh7robmw]

Maybe I'm noticing the burbling and popping more now as we're at 3800-4000 feet asl here. One road goes up to 6700 feet before coming to a deadend. Perhaps this is a contributing factor.

The main thing though is apparently this is not usually a problem; just the nature of the beast.

[Gilly]

I was always a little concerned I might burn an exhaust valve, but I sold it at 95000 and didn't seem any the worse for wear.

[tricyclerob]

Jeff,
There is, I believe a "high altitude" plug for the K's. It's like a little "jumper wire". Not sure where it goes, maybe someone else can jump in here, but I believe it came with all the K bikes. Every once in a while there's one on e-bite. I'm also not sure what they considered "high altitude".
Also, since that orig.post, I did adjust the TPS, and that did help some, but fully closing the throttle helps more. rj

[nh7robmw]

Thanks, Rob; I was wondering about using the altitude plug--kinda iffy though in my situation---once I leave our immediate vicinity the highway out of town is all downhill (back to sea level in 25 to 40 miles depending on direction).

A nearby side road goes up to 6700' and another road across the middle of the island hits 6000' but I only will be on those roads occasionally. Most of the highway that rings the island runs between 1000' and 2500' asl.

Yet since the exhaust deposit around the tail end of the muffler is dark and sooty I suspect it's running a bit rich regardless of the altitude.

Perhaps my best bet is to try to rig up one of those altitude plug switches that I can use whenever I'm above 2 or 3000 feet. I'll search the forum or IBMWR on how to do this as I plan to try this out at some point in the near future---thanks for your helpful suggestion; I'll let you know if it makes a difference.

In the meantime, I checked the TPS and I only hear one click, almost immediately upon twisting the throttle open. Then I hear something different once the throttle is stopped (like it hits a set screw or something) when opening it all the way. Not sure where the little box is located but I checked it only briefly to see if I could hear those clicks everyone has told me about.

I'm working longer and later shifts at work this week and next so I won't have the proper time (and energy) to really pursue this properly right now.:burnout I will see what I can find out about the altitude plug in the meantime, though, and that might just be the easy fix at hand.:idea

[deilenberger]

Thanks, Rob; I was wondering about using the altitude plug--kinda iffy though in my situation---once I leave our immediate vicinity the highway out of town is all downhill (back to sea level in 25 to 40 miles depending on direction).

A nearby side road goes up to 6700' and another road across the middle of the island hits 6000' but I only will be on those roads occasionally. Most of the highway that rings the island runs between 1000' and 2500' asl.

Yet since the exhaust deposit around the tail end of the muffler is dark and sooty I suspect it's running a bit rich regardless of the altitude.
Anything over about 1,500 feet and it's running rich.

Perhaps my best bet is to try to rig up one of those altitude plug switches that I can use whenever I'm above 2 or 3000 feet. I'll search the forum or IBMWR on how to do this as I plan to try this out at some point in the near future---thanks for your helpful suggestion; I'll let you know if it makes a difference.
That's the best solution. You'll find the wire/connector for the altitude plug (which is simply a jumper) on the left side of the bike, normally tie-wrapped to the downtube right in front of the ECU. Look for a wire with a black lump on the end about 3/8"D x 1" long. Pull on the end of it - and it will come out - there is a cap sealing off the actual connector. Most people who add a switch just cut the connector off and splice in wiring going to an easily reachable switch.
In the meantime, I checked the TPS and I only hear one click, almost immediately upon twisting the throttle open. Then I hear something different once the throttle is stopped (like it hits a set screw or something) when opening it all the way. Not sure where the little box is located but I checked it only briefly to see if I could hear those clicks everyone has told me about.
The TPS is the black box on the back end of the throttle body assembly. One click just off idle is normal, and you may be able to hear a click going to idle IF you close it very slowly. The click at WOT is to tell the ECU to richen things up for max power - something I don't think you actually need at the moment.
I'm working longer and later shifts at work this week and next so I won't have the proper time (and energy) to really pursue this properly right now.:burnout I will see what I can find out about the altitude plug in the meantime, though, and that might just be the easy fix at hand.:idea
I suspect the altitude plug may solve most of your problems - the bikes are down a lot on power and economy when at altitude..

[nh7robmw]

You answered all of my questions; all I need to do is connect that altitude plug and round up a switch that I can mount on my handlebar dashboard (suppose A&S will have the BMW switch that fits in the accessory slot there) and I should be good to go up and down the mountain.

Cheers!:german

[roncooper]

I put the switch on a bracket that I fastened to the left battery hold down bolt.
The switch handle points down, and I can reach it easily while riding. I did it that way to prevent having to "snake " wires up to the handle bars.

[nh7robmw]

Just went out and looked all over the left hand side of the bike and found the altitude plug well tucked away behind the frame. Short lead.

Pulled the plastic cap off and saw the tiny pins inside---which quickly gave me an idea---balling up a small piece of aluminum foil to stick inside the cap which would short out the pins and therefore "activate" the high-altitude lean-out. Nifty quick-fix, eh?

I'll probably do this as a temporary measure until I decide whether to go ahead and get the proper jumper plug or cut the lead and solder in a switch instead. I'll carry some tweezers with me so I can remove the foil whenever I go below 1000 feet.

I'll be in town tomorrow so will stop by Radio Shack and get a rocker switch and some hookup wire since that is probably the way I'll want to proceed...

I won't try adjusting the TPS until I've done this mod and ridden a while with the plug in effect since I may not need to do anything else.:bikes

[nh7robmw]

Just went out and looked all over the left hand side of the bike and found the altitude plug well tucked away behind the frame. Short lead.

Pulled the plastic cap off and saw the tiny pins inside---which quickly gave me an idea---balling up a small piece of aluminum foil to stick inside the cap which would short out the pins and therefore "activate" the high-altitude lean-out. Nifty quick-fix, eh?

I'll probably do this as a temporary measure until I decide whether to go ahead and get the proper jumper plug or cut the lead and solder in a switch instead. I'll carry some tweezers with me so I can remove the foil whenever I go below 1000 feet.

I'll be in town tomorrow so will stop by Radio Shack and get a rocker switch and some hookup wire since this is probably the way I'll want to eventually proceed...

I won't try adjusting the TPS until I've done this mod and ridden a while with the plug in effect since I just might not need to do anything else.:bikes

[nh7robmw]

:doh

[nh7robmw]

Your switch mounting idea also sounds like another good idea, Ron. That would also leave me that dash slot open for an auxilliary lighting switch, too.

[Gilly]

"Reynolds Wrap Switch Co"

[98lee]

High Altitude Adjustment

"If the bike is going to be ridden for any sustained period of time at high elevations (1,200m/4000ft.) the fuel system must be modified electronically to improve performance and decrease exhaust emissions. A small wire loop, available at BMW dealers, is added to the electronic circuit to compensate for altitude change."

(Clymer K-Series 1985-1995)



:dance :dance :dance

[nh7robmw]

Had some time today to get to the bike and try out my "Reynolds Wrap Altitude Plug."

Plugged up the cap with a small piece of foil and stuck it into the AP. Proceeded on a fast (around here fast=60 to 80+mph) 35-mile ride around the highway and along some side roads---abruptly cutting the throttle produced no more burble or popping whatsoever---very smooth, indeed.:whistle Don, you were right about this 100%

Also did a modification to the windscreen that was an equally noticeable improvement; much more of a calm airspace behind it that seems free of the turbulence I was plagued with previously.

So this turned out to be a very satisfying and productive day for me and my K. Don't think I need to mess with the TPS at all now---whoopee.:german

[JHGilbert]

I ride daily and our elevation is 3800 feet. My tail pipe always has a black, sooty deposit. I tried the high-altitude plug, but my header pipes began turning blue, which to me indicates too lean and high exhaust temps, increasing the possibility of burning a valve. Any thoughts or solutions to getting the mixture a little closer to correct?