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Discussion Starter #1
Ok here goes. Chicago finally warmed up a bit to go out for more than a 15 minute ride. Over winter I replaced the input shaft and replaced the clutch in my 87 K75s. I have ridden for several 15 minute short trips and tranny seems all good. I decided to give a tune up to de-winterize the ol girl thus checking valve clearances and throttle body sync. This is where I ran into problem beginnings. I had read about the TPS "click" and was getting none. I repositioned the switch and now I get the "click" but it also seemed to put my idle high and not allow throttle to completely close. Re-adjusted the TPS to click and not hold idle positioner open.
I only have some dial type vacuum gauges to try and sync the bodies and all were pretty damn close to one another.
Today the bike performed fine until about 20minutes into the ride and then I am getting pretty dynamic power surges and terrible throttle response sputtery exaust (more than normal) Pops when rolling on the throttle. Last year I replaced the common dried rubber hoses and such so I am feeling like it isn't air leak. Also upon coming back to my toyshop I saw this little cap sitting loose near the fuel rail. Please Please! any help and advice would be greatly appreciated.
 

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Quick and dirty test for air leaks: Start the mc and remove the oil filler cap. You now have a self-created vacuum leak. The mc should get lumpier/rougher. If not, you probably already had one. You didnt mention how the mc is idling. If the problem is only while running: put the mc on the centerstand. I usually put a board under the centerstand to get a little more distance between the ground and the wheel. Put the mc in gear and run until the problem reappears. Then remove the cap and see if there is a difference. Please do not run the mc into your garage wall.

My K75 had similar issues in freezing temps and high altitudes toward the end of its life. Fine in warm weather. Mildly irritating in cold temps at lower elevations. Never figured it out. Best guess was vacuum leak due to worn rubber which only manifes:)ted under extreme conditions. This was before I knew about the oil cap test and the crank case breather hose.

Re: the TPS. Bosch manual for LE-Jetronic is available for DLing as a pdf at many sites. The TPS has two contacts inside. One indicates throttle off and the other WFO. That is it. Minimum gas and maximum gas. Two switches. The controller gets no info from the TPS when the throttle grip is in intermediate positions. The air flow sensor handles that job. At WFO, fuel economy and emission control are not the controlling factors. The control unit is designed to deliver a fuel mixture for maximum power. One reason for the throttle closed switch is so the control unit can shut down the injectors at the proper time when you go from throttle on to throttle off. Without this, in situations such as from WFO to closed, the fuel injectors would not decrease the amount of fuel in sync with the decreased amount of air. You would get a rich mixture of some sort. This results in the popping exhaust sound. You also get this if you fail to completely close the throttle when rolling off the gas. I did this regularly when I first got my K75. It was duck and cover eveywhere I went.

The point of this is the manual says failure to properly set the TPS can result in the popping noise even if you close the throttle completely when rolling off. In this case, you have set the TPS so the switch which indicates throttle off is not activating. So, the control is not shutting down the injectors in the way designed to prevent overrun. You do get decreased fuel as the air flow sensor sends its signal to the controller. But the specially designed shut off at throttle off does not occur. BUT THIS IS AT ROLL OFF, NOT ROLL 0N. As far as I can tell, TPS does nothing on roll on until you hit WFO. Unless you have misset the TPS so badly the WFO switch activates very early, missetting the TPS should have no effect on moderate roll on. I do not know what the effect of early activation of the WFO switch would be.

The click you are hearing with the throttle grip forward must be the contact closing. That means the controller should be shutting down the injectors to prevent overrun. Presumably there is a click at WFO to indicate that switch is working, but I havent tried that. If I remember I will try that tomorrow to see if I can figure out when the WFO switch closes.

I am not an expert in LE-Jetronic. I have studied the manual to get a basic understanding of the system. A guru may correct me here.

Is the cap rubber\vinyl? I havent run a K75 for 5 years, but I have a vague recollection of two small black rubber\vinyl caps that cover open-ended tube spars that came out of the main frame under the tank somewhere. One on each side? Mostly decorative I thought. Maybe kept water and dirt out of there.

Good luck. I would triple check for a vacuum leak. That is an easier fix.
 

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I think your little cap is the protector for the end of the throttle shaft at the very front of the throttle bodies.

Some of the later bikes had such a cap and some have found it laying there. I say some....not even in the parts fiche and no such thing on my later bike but yeah may have disappeared somewhere on the road back then.

Shouldn't affect the vacuum unless dirt got in there and wore out the throttle shaft, doesn't seem to be your case if vacuum readings hold steady. Vacuum leaks would certainly show as fluctuations on the gauge or "no vacuum" if a big leak. That may not show at idle the small leaks, you may have to use the throttle a little and see what the gauges are doing.

But popping/sputtering.....how good is the gas? Just asking because my little XR did just that with relatively fresh gas, took a while to clear what I think was water getting sucked in.Also fuel filter? Just had to replace mine at way less than the recommended interval, was plugged almost solid and moisture/water will also swell the filtering media and plug it.Yep been through that with the K100RS, only took a batch of bad gas and sure did not want to run well, with symptoms very similar to yours.
 

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Discussion Starter #4
Thanks 97 for the in depth response! Brilliant idea for the quick vacuum test I will certainly be doing that today along with another close inspection of potential leak zones.
To mention the bike at idle, I definitely have a stutter or stumble at idle. also the day was mild about 57 degrees. The surging problem is most noticeable at lower speeds and off the line I have really rough throttle response. Highway speeds its much less noticeable but the bike is much less punchy than it used to be.
I'm pretty certain I haven't grossly mis-set the TPS. I get a click just as freeplay of throttle takes up and another when I close throttle.
Back to the toy shop today. Thanks again
 

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Discussion Starter #5
H96669 said:
But popping/sputtering.....how good is the gas? Just asking because my little XR did just that with relatively fresh gas, took a while to clear what I think was water getting sucked in.Also fuel filter? Just had to replace mine at way less than the recommended interval, was plugged almost solid and moisture/water will also swell the filtering media and plug it.Yep been through that with the K100RS, only took a batch of bad gas and sure did not want to run well, with symptoms very similar to yours.
H9, Thanks for the tips. I was looking at the throttle shaft end as well thinking that was probably the home for that little cap. It must have very recently come off so I don't imagine wear yet.
As for the gas, who knows about quality with these city gas stations. Could be half water these days. I filled the tank with Mid the day this problem arrived. I also threw in some HEET to try and wrangle any winter moisture.
I replaced the fuel filter last season but did get a good amount of water into the tank from water sitting under cap when I opened it. But that was several tanks ago. I will try swapping the filter out if I can get my hands on one quickly. Thanks again.
 

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When you synched the throttle bodies, you removed three rubber caps. Did you closely examine them before you put them back on? They can get brittle, crack, and leak. New ones are available at local parts stores, usually in a variety pack but very inexpensive.

Larry Johnson
El Paso Tx
 

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Discussion Starter #7
ljjohns said:
When you synched the throttle bodies, you removed three rubber caps. Did you closely examine them before you put them back on? They can get brittle, crack, and leak. New ones are available at local parts stores, usually in a variety pack but very inexpensive.

Larry Johnson
El Paso Tx
Thanks Larry, Caps are brand new from auto parts store. at least I can check that one off the list.
 

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Discussion Starter #8
Update to missing smooth

spending the day in the toy shop I have just discovered that when the bike is idling and I wiggle the rubber boot on the third injector the idles bogs dramatically. The 2 other injectors toward the front do not have the same effect when manipulated. Any thoughts on this? Thanks again for all the advice.
 

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Discussion Starter #9
New update

So I pulled the connector at the top of the third injector that seemed to be shorting out and low and behold it looks like it has gotten a little cooked. Any thoughts on if this could be part of my problem and why it would happen. Thanks tons
 

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I found enough greenish/whitish connectors on my much later bike to know about the why.Mostly road salts eventually seeping in there but could be salty sea air or even just normal moisture. You should follow the BMW bulletin that recommends cleaning and protecting all the connectors on their bikes once a year. Old bulletin but still valid.

Pretty small wires also, it may be broken inside the sheating and you can't see the break.May need to find the other end and put the Ohmeter to it and wiggle to look for continuity.

Better stuff and availability nowadays as to dielectric greases and electrical cleaners. Did my bike 2-3 years back, re-inspected this year and still all good.No need to follow the "once a year" bulletin as long as it gets done with some regularity.
 

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San Jose Injector cover

Glad you found the problem.

I have seen one K75 with an injector cover. The owner put it on to keep the injector area clean. That was an angled sheet of aluminum. San Jose BMW advertised one which it touted as making the injectors tamper proof. Here is a photo.




Never seen one of these. Dont know if still available.
 

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Discussion Starter #13
97tiger885 said:
Glad you found the problem.

I have seen one K75 with an injector cover. The owner put it on to keep the injector area clean. That was an angled sheet of aluminum. San Jose BMW advertised one which it touted as making the injectors tamper proof. Here is a photo.




Never seen one of these. Dont know if still available.
Thanks! I'm going to sync TBs again since I may have been tuning to something off a bit. I like the cover idea. Need to take her on a long run and get her heated up and make sure all is well. now. Thanks again.
 

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Discussion Starter #14
FlyingDuck said:
You can also DIY one out of aluminum sheet and then have it powder coated.

Now you're speaking my language! I am a fabricator by profession after all. I see an evening with the tig in my near future. Thanks
 

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Discussion Starter #15
Smooth still gone

Well I thought the stumble was fixed with the cleaning of injector connector but it is still there. I checked fuel pump pressure over at Seymour Goldbergs shop here in Chicago. He was super busy so we couldn't chat more but the pressure was fine at idle so I know I am getting the fuel pressure I need. Although in hindsight I never gave throttle to see if the pressure changed. I notice that when I start the bike cold the battery light flickers with the same rhythm that the bike seems to stumble. Could this be a piece of the puzzle? I'm going to go through the bike and check connections and other potential rubber culprits again and see what more I can find. Any more suggestions to solve this surging problem would be greatly appreciated. Trying to get ready for my annual ride and camp through the Smokies.
 

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flyrigger said:
Well I thought the stumble was fixed with the cleaning of injector connector but it is still there. I checked fuel pump pressure over at Seymour Goldbergs shop here in Chicago. He was super busy so we couldn't chat more but the pressure was fine at idle so I know I am getting the fuel pressure I need. Although in hindsight I never gave throttle to see if the pressure changed. I notice that when I start the bike cold the battery light flickers with the same rhythm that the bike seems to stumble. Could this be a piece of the puzzle? I'm going to go through the bike and check connections and other potential rubber culprits again and see what more I can find. Any more suggestions to solve this surging problem would be greatly appreciated. Trying to get ready for my annual ride and camp through the Smokies.

I only have my usual list of suspects. First, stuff even I can do.

One possibility is all the spark plugs arent firing properly. Power surges are the result of running 3 and 4 cylinders at various times. And the popping is the result of one cylinder running rich as it fails to fire one cycle but fires the next with two cycle's worth of gas. There are two possibilities there. First is a spark plug wire issue. One might be loose or compromised. Second is a bad coil. Two cylinders would be firing irregularly. I am lucky. I have a friend with two K100s being rebuilt. I have access to lots of parts. If you could borrow someone's known good coils, then you could use those to see if the problem goes away.



How do you know cleaning the connector worked? Does wriggling the connector no longer have an effect?


You could do the same with the fuel filter. Weirdness happens with bad filters. Maybe you have/had a bad tank of fuel. Put in new fuel and a new filter. That is easy. If it is not the filter, put the old one back in and keep the new one for the next service.

Then there is the vacuum leak issue. I would double check the crank case breather hose. Recent replacement is no guarantee. I bought two from Bobs. The first had cracks after a year. I wrapped the second with electrical tape before installation. The o-rings on the injectors are a possibility too. There are two on each injector. Be warned. There is a good chance you will damage these if they have been on for a while. Have replacements ready. VW dealers have a kit for $16 which includes 3 o-rings, a nozzle cap and a support washer. The support washer is the wrong size.

Good luck. I feel your pain.
 

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Not good for the electronics disconnecting the wires with the engine running on electronic ignitions. Could turn expensive, and often....shocking. :teeth

There is a way to short them, shutting one cylinder at a time with a wire shunt to ground.That is commonly used to balance/tune the old airhead twins with electronic ignitions. Not sure if that would work in that tighter location on the Ks. I think so.

If the casing is damaged, could show as pinholes and sometimes hard to see. May be possible to run the bike in the dark and look for sparks to ground. You can even spray water there and possibly see more sparking.That's how I found the missing/hard to start problem of my little XR.

Carbon wires degrade internally also, hard to see. On those K75s you can't check them with the Ohmeter. That test on my later bike quickly showed me the defective wires.

I have a number of known good wires here, would be just a matter of finding one that fits both ends and switch it around the cylinders and look for an improvement.
 

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H96669 said:
Not good for the electronics disconnecting the wires with the engine running on electronic ignitions. Could turn expensive, and often....shocking. :teeth

There is a way to short them, shutting one cylinder at a time with a wire shunt to ground.That is commonly used to balance/tune the old airhead twins with electronic ignitions. Not sure if that would work in that tighter location on the Ks. I think so.

If the casing is damaged, could show as pinholes and sometimes hard to see. May be possible to run the bike in the dark and look for sparks to ground. You can even spray water there and possibly see more sparking.That's how I found the missing/hard to start problem of my little XR.

Carbon wires degrade internally also, hard to see. On those K75s you can't check them with the Ohmeter. That test on my later bike quickly showed me the defective wires.

I have a number of known good wires here, would be just a matter of finding one that fits both ends and switch it around the cylinders and look for an improvement.
I talked with a more experienced K100 rider. The spark plug idea IS DANGEROUS if not done properly as H69996 points out.. The plug must be grounded when the engine is running or damage to expensive electronics is a real possibility. That means engine off, spark plug out, plug grounded to engine block with clamp, engine on, plug check, engine off, plug back in.

Here are some other possibilities.

Spark plug failure. Not common but a potential problem. Pull the plugs and check.

Spark plug lead failure. As suggested, remove cover plate to plugs and mist area GENTLY with water. If done at night, arcing due to cracked insulation will be observable.

Loose lead. Remove plug cover. Take each lead and jiggle trying to change quality of connection.

Clogged injector. This is not direct injection. At least part of the time, the injectors spray onto the valves and the air flow from the throttle bodies delivers the fuel. But the pattern still has an effect on how the engine runs. The test is to remove the fuel rail with injectors attached. Take large glass container and half fill with water. Place injectors in container over but not in water. Have someone start mc. Observe spray pattern of each injector. Correct pattern is round. Water is there to keep gas from bouncing off glass onto mc. THERE IS FIRE DANGER HERE. TAKE CARE.

Bad coils. Idiot test. Borrow known good coils.

Bad pick up sensor. The pick up sensor is located on the front of the engine behind the small cover on the left side. Remove cover. Do not move sensor without carefully marking its position. Start engine. Test is to use heat gun on sensor. If heat exposure worsens the problem, sensor is probably failing. This is a very expensive part.

Bad signal to fuel injector. A very small current is used to open the injectors. A device call a NOID is used to verify current. This is a small ovoid device with a light which plugs into the injector harness in place of the injector. The current causes the light to come on. I am told it is available from VW for a reasonable price. Many VWs used L-Jetronic.

This is making me paranoid about my mc.

A lot of stuff can be found on the IBMWR site in the K tech pages.
 

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The Hall Sensor, pretty expensive that thing. :yeow: But there is a way to replace the sensors on the plate with inexpensive components.

There is also a way to check the timing with an adjustable timing light. That's in the IBMWR site and may be easier than the established BMW procedure,that one requires special tools I haven't felt the need for just yet.

Makes me wonder...there is a seal there and if it leaks engine oil will find its way on the pick-ups and may cause problems.That happened to someone after his new seal installation failed, newer version of the seal is Teflon and has to be preformed and that can be tricky. Even the cork gasket for the cover, my later bike was missing a bolt and water found its way in there, that could have affected things if I had let the corrosion build up.
 

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Discussion Starter #20
97tiger885 said:
I talked with a more experienced K100 rider. The spark plug idea IS DANGEROUS if not done properly as H69996 points out.. The plug must be grounded when the engine is running or damage to expensive electronics is a real possibility. That means engine off, spark plug out, plug grounded to engine block with clamp, engine on, plug check, engine off, plug back in.

Here are some other possibilities.

Spark plug failure. Not common but a potential problem. Pull the plugs and check.

Spark plug lead failure. As suggested, remove cover plate to plugs and mist area GENTLY with water. If done at night, arcing due to cracked insulation will be observable.

Loose lead. Remove plug cover. Take each lead and jiggle trying to change quality of connection.

Clogged injector. This is not direct injection. At least part of the time, the injectors spray onto the valves and the air flow from the throttle bodies delivers the fuel. But the pattern still has an effect on how the engine runs. The test is to remove the fuel rail with injectors attached. Take large glass container and half fill with water. Place injectors in container over but not in water. Have someone start mc. Observe spray pattern of each injector. Correct pattern is round. Water is there to keep gas from bouncing off glass onto mc. THERE IS FIRE DANGER HERE. TAKE CARE.

Bad coils. Idiot test. Borrow known good coils.

Bad pick up sensor. The pick up sensor is located on the front of the engine behind the small cover on the left side. Remove cover. Do not move sensor without carefully marking its position. Start engine. Test is to use heat gun on sensor. If heat exposure worsens the problem, sensor is probably failing. This is a very expensive part.

Bad signal to fuel injector. A very small current is used to open the injectors. A device call a NOID is used to verify current. This is a small ovoid device with a light which plugs into the injector harness in place of the injector. The current causes the light to come on. I am told it is available from VW for a reasonable price. Many VWs used L-Jetronic.

This is making me paranoid about my mc.

A lot of stuff can be found on the IBMWR site in the K tech pages.
Whew! Thanks for all the advice. I'm going to try and avoid any potential new problems by cooking something with the "spark plug idea"
As far as plugs go, all three have a nice toasty brown color as they should. I will tonight check with some water spray if they are leaking juice somewhere. I replaced the fuel line that goes to fuel pressure regulator as it had some surface cracks. The cracks didn't seem very deep but who knows. Could be the culprit. I found the cracks when I pulled the airbox out to check the Mass Airflow Sensor. The sensor door moves freely so this evening I was going to pop the black cover off and give the resistor strip a gentle cleaning with contact cleaner. I was going to put her back together and test run. I don't want to fidget with too many things or I won't know what fixed it.
Next on the list will be test resistance on temp sensor to see if is any good. Any one know what that resistance should be? I am going to go through with a fine tooth comb and clean and grease electrical connections and check and recheck grounds. I will also try the heat gun on the Hall sensor.
This is driving me nuts so I hope you "97" don't run into it as well. Maybe if I can figure it out first you won't have to be paranoid. Thanks again for the tips, don't give up on me.
 
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