Hi all,

I've been lurking the forums for a while trying to figure things out. Just want an opinion of what you think my issue may be. Picked up an 86 k100rs with 27,000 miles on it. It had been sitting for a long time and he no longer could get it started. I got the bike home, and she fired up with a little hesitation, backfired and smoked for a minute, then smoothed out. I rode the bike for about 5 miles with no apparent issues before she suddenly died. Wasn't able to get it started again and had her towed back to the house.

First thing was first, I couldn't hear the pump. I was surprised it actually worked for 5 miles after I pulled it out (it was rusted bad). Also, the previous owner had coated the inside of the tank with a sealant a long time ago, and that sealant paint was peeling inside the tank. So I spent a few days and removed all of the sealant from the tank, I replaced the fuel pump, I replaced the fuel filter. Again she wouldn't start. Pump was not working. I eventually poked and prodded with a multimeter and found that the fuel level sender unit and power leads had a short in them right at the junction of the wires into the tank. Since the fuel level sender unit was rusted, I simply removed it and re-soldered the power lead (ground was still good) to one of the sender unit leads.

The bike came back to life, somewhat. Got a block down the road and it started sputtering again and stopped.

Here are the symptoms:
Starts fine
Idles fine
bogs down when given a touch of the throttle but can get it to rev to about 3k rpm before it bogs down again and dies.
smells flooded


I've changed the spark plugs, old ones were wet and semi fouled.
I've checked the spray pattern of the injectors and they seem to be misting just fine.

Now I have the air box out and the FPR out. When I removed the FPR, there was positive pressure on the rail side of the FPR (it sprayed pretty good). I'm going to try the best I can to test the Air Meter according to the trouble shooting guide, but will need to go get an temp gauge first.

Any ideas as to the symptoms described?

Yep,
Similar to my experience and found a dirty connector from the tank, the one you disconnect when removing the tank.
If a bike is running OK before it was stored then it will be without doubt dirty connectors, or old petrol, go clean everything you see with regard to harness connectors. A pity you didn't do this thoroughly at first and it would have saved you a lot of money.
BTW, take a look at the download page, you will find it very helpful.
Ajays

Thanks for the reply Ajays. I did test the connections all around, and all seemed ok. I did not however use any contact cleaner, which I think I will do this evening. If DeOXit is not available locally, is there any other recommendations on contact cleaners?

Edit:
This is available locally, I will give it a try. CRC QD Electronic Cleaner

De-Oxit comes highly recommended and possibly its main advantage is its protective qualities but I would suspect any top end cleaner you can get will work well or at the very least be an improvement.

So I put it back together and fired it up, it still sputtered. I took it to my car and hooked up the jumper cables (battery light comes on when it sputters). I let it sit there idling for a while, and I could rev very easily with no hesitation while it was connected to the car battery. After letting it sit on the car battery for 15 minutes, I disconnected the car battery and tried to go, made it 30 meters before it sputtered and died.

The previous owner said the battery was almost new, but now I'm thinking I just need a new battery. Would this be the cause of my symptoms?

Also, how would one go about testing the alternator/generator?

Could still be as simple as a dud battery but we need to know what the voltage of the battery is and once it is running what voltage do you get across the battery terminals.

Does the charge light come on with the ignition and go off at about 1400 revs?

The alternator does not produce full charge until around 3000 revs and should be about 14V.

I won't have the opportunity to check until tomorrow (the old ladies in the neighborhood will get after me for revving it above 3000).

The charge light comes on if I try to throttle up and am not connected to the car battery. I am going to go purchase a trickle charger and charge it up over night. Tomorrow morning I should be able to test it out and see if it was simply a battery.

My roommate, a bmw car master tech, says its impossible that its the battery. He says if the battery was junk, it would have never started as many times as it did. :/ I will still get the trickle charger, but not sure this is the problem.

Chad,
Your "Car" master tech could be wrong you know, I still think it is electrical and the standing battery whilst in storage I would certainly suspect.
Invest in a new battery and get a gel type to save aukward maintenance.
A word of warning, Do Not attempt to start your bike on a low battery. You will cause problems with the starter relay points.
It will be solved here on this forum eventually have no fear. The big guns will come in after a while.
Ajays

Last year I had a similar problem on the K100.
Went out for a ride and stopped at a store. (The bike was running perfectly)
5 min. later, I restarted the bike but it would not idle anymore. I had to keep the engine at a minimum of 2,500rpm in order to go back home.
I parked the bike in the shed and decided to check it later.
The next day, the bike started perfectly and idled at 800rpm until it warmed up. then it started to run really crappy. Let it cool down and restarted, same as before: as soon as the engine was warm, it crapped out.
I checked the spark plugs, FI, ignition and then, the battery went dead.
The battery was fairly new and I couldn't understand. I got the battery of the K75 and the K100 re-started and it ran without any problems.
After charging the K100 battery for only 15 min, it was working again and I couldn't replicate the problem.
Why the bike was running crappy only when it was warm? this is a big mystery but since I permanently replaced the battery, the problem never re-appeared.

Bert

The battery I have installed is an xtreme AGM 30 Ma battery... I've never heard of it. It looks fairly new. Last night I permanently mounted a small 1.5a battery tender in the tool box under the seat, so I simply only need plug in an extension cord when it needs charged. I will test it after work today and see if this alleviates my problem. Thank you again for the help guys, lets keep our fingers crossed that this is the issue!

On a side note, I did pick up this nice headlight bucket off ebay to retrofit to the k100! BMW Headlight

The Chad wrote:Thanks for the reply Ajays. I did test the connections all around, and all seemed ok. I did not however use any contact cleaner, which I think I will do this evening. If DeOXit is not available locally...
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Try a decent music store, this product is used to clean sound/mixing board controls too. That's where I found mine. Expect to pay about $20 for a small can.

Go to Caig Labs website and look for a local dealer they have a list. Also get your multimeter and measure the voltage across the battery, that will tell you once and for all what the voltage is. With the alternator fitted the battery is not charging at idle only above around 1400 rpm
Regards,
K-BIKE

It wasn't the battery, still having the same issue. I noticed that the fan is not coming on at all, but neither does the temp light. The bike sounds good, revs fine, accelerates smoothly for about 3-4 minutes, then as soon as it gets warm, it just bogs down and i lose throttle response. It will idle though for a while. I am going to check the fan switch tonight. The fan does spin freely if i nudge it with my finger.

The fan should only come ON when the water temperature is over 103 Celsius.
The temperature light doesn't come ON when you turn the ignition key. It will only come ON if the engine overheat.

If you think that your engine overheats, You should check the water temperature sensor. The water temperature is one parameter used by the Fuel Injection computer.
See the fuel injection troubleshooting page to get the expecting reading of the sensor.

Bert

Chad,
I think you are wasting your time with the fan, as long as it spins OK that will not be your problem...you did say you fitted a new filter (in the tank) I believe,... is it the correct way round?
You could have this behavoiur if your tank cannot breath, there is a breath tube under the tank you may have trapped. When you open the cap do you get a bonk. Try it with the cap open ajar and do your run thing.
Ajays

New filter is in correctly and tank breathes.

I also forgot to mention that I do not have the front signals, horns, or headlight connected, but I dont think they mess with the FI at all... correct me if im wrong.

I am going to go for a spin with the tank open just to see, but I have a feeling this isnt it. Symptoms are like vapor lock but not coming from the tank, could the lines have air in them or something?

I strongly suggest that you follow the advice given by Bert above at 3.42, that is go to the fuel injection troubleshooting page he references above and work progressively through the items one by one starting at the beginning. You will need a quality digital meter but every owner of an old car or bike should have one (the lowest cost option) or be prepared to take the machine to a dealer that does and pay someone else to use one (the highest cost option). Bert has with assistance from others assembled a very effective diagnostic tool to enable one to define and isolate the problem.

The alternative (as used by many garages these days) is to make wild guesses and replace bits piecemeal until they stumble upon the result. Of course they don't put back all your old bits which changing out didn't make any difference but you will have a bike with a new fuel pump, filter, ignition module, temperature sensor, fuel injection brain, injectors, fuel hoses, airflow meter, spark plugs, leads, and oh a very much thinner wallet. If the problem was a bad ground in the first place and they don't by accident find it the problem won't be fixed and they will pronounce themselves stumped and cut you adrift. Sorry to be so pedantic but logically working through Bert's system is your best chance of a reasonable cost solution. All over the BMW internet groups people are extolling the virtues of his troubleshooting process it really does work.
Regards,
K-BIKE

I have been going through the FI troubleshooting guide for 2 weeks now and have done everything except replace the injectors (spray pattern is fine) and check the fuel pressure via a manometer. I've checked/cleaned everything electrical connection outside the temp sensor. The bike runs fine and purrs but ends up dieing and choking (rich) after a few minutes.

Here is something else:
First a quick explanation....
The 4 injectors are working together.
As long as the FI computer receives a signal that the crankshaft is rotating, it provides power to the injectors. What if one of the Hall sensor is defective? The FI computer still receives a signal that the engine is running from the good sensor. The bad sensor will provide an erratic or no signal to the ignition computer and basically your engine will run on 2 good cylinders and 2 bad ones.
Have you checked these sensors?
If not, start your bike cold to be sure that it runs well.
shut off the engine and warm up the Hall sensors (a hair dryer is working well for this). When the sensors are hot maybe 80 to 90 degrees (they are rated to operate to a temperature up to 160 degrees Celsius) try to start your engine to see if it's still running as smooth as when cold.
Let us know your finding.

I checked the Hall Sensor with a hair dryer. Idled fine before, revved fine. I heated up with the hairdryer, started just fine and idled. I kept the hair dryer on for 5 minutes and no change.

So I hopped on the bike and listened carefully.... I have another clue. The fuel pump (which I just replaced), whines pretty good idling (enough that you can hear it). But as soon as I give it gas, it slows down and stops whining. When I pull the clutch back in, it starts whining again. I tried with the TPS unplugged too and same results, stops whining when clutch is out and throttling (stops altogether it seems). Bike starts to sputter and die.

I am interested with your problem. This is a good challenge.
Give me a bit of time to think about it.
If it wasn't the fact of the bike acting only when hot, I could have some idea of where the problem could originate from, but please lets start with the basic. Could you put a voltmeter in parallel with the power to the fuel pump to monitor the voltage?

Bert

Thank you for all your help. Unfortunately i decided to go to the beach for the weekend so I will get back to you Sunday with the results. Cheers!

When you give it gas the vibration level increases are you getting intermittent connection on the power feed to the fuel pump? Possibly from the connector plug/socket which comes off the tank? Or at the big plug into the fuel injection brain these are known to not quite click home and then cause problems often rev/vibration related. A dodgy fuel injection relay or relay base could cause the problem if there was rev related vibration. Similarly a poor connection between the ignition module and the relay especially if warming it up caused expansion. It will be interesting to see what voltage you have on the fuel pump as Bert says.
I will think some more.
Regards,
K-BIKE

I still think it is a connection at the tank . As I said before.
I put a tie round the big plug to ensure it doesn't come loose. Been there.
Round holes I used a drill smaller than the hole and push it up and down to scrape the inside. I didn't use cleaning fluid ever, manual scraping I favour then Vaseline/Petrolium Jelly. This I have used in the distant past in the 50's.
I think K-Bike has a strong point with regard to vibration and poor contacts.
Ajays.
I am sure it is simple...don't throw a lot of money away as I am sure you have already done.

Ajays wrote:I still think it is a connection at the tank . As I said before.
I put a tie round the big plug to ensure it doesn't come loose. Been there.
Round holes I used a drill smaller than the hole and push it up and down to scrape the inside. I didn't use cleaning fluid ever, manual scraping I favour then Vaseline/Petrolium Jelly. This I have used in the distant past in the 50's.
I think K-Bike has a strong point with regard to vibration and poor contacts.

Well I already re-soldered the bottom tank connection (at the sender) and tested it... then I covered the connections inside and outside of the tank (again at the sender) with gas tank polypropylene plastic weld. Its not likely, but possible they vibrate loose. I also cut the tank connection right off and crimped the wires together. I am going to replace them with a solid aftermarket quick connect tonight as well as test for loose connections under vibration.

Thanks for all the help again! Hopefully I find the problem soon.

Ok so I hooked up the multimeter inside the tank to the pump... 12-14v at all times... So this is not the problem. I noticed that the fuel pump is actually pretty quiet and the whining I am hearing is coming from somewhere else. I'm beginning to think it may be a tiny air leak of some kind making a noise because of the pressure escaping... I also have yet to test the fuel pressure on the bike.

I also need to note that it does happen after the bike warms up a tad and worse when under load. If I put the bike on the center stand and put it into gear, I can "drive" it much longer than if I actually try to drive it under load on the road. On throttle it seems it missed (rpms drop to nothing) and then it catches itself up to only about 1500 rpm before it bogs down.

Is it the return valve in the return stub inside the tank?

ReneZ wrote:Is it the return valve in the return stub inside the tank?

I am not sure what you mean...

The early Ks had a return valve mounted inside the tank. This valve was there to avoid having the fuel pouring out of the tank when removing the hoses. On these models, the gas was returning to the bottom of the tank
In 1986, BMW changed the design of the tank to have the return line going internally to the top of the tank. This modification resulted to the removal of the return valve.
This is another reason to provide the serial # of your bike.
If I had it, I could right away tell you what type of tank you have.

Cheers

Bert

Crazy Frog wrote:The early Ks had a return valve mounted inside the tank. This valve was there to avoid having the fuel pouring out of the tank when removing the hoses. On these models, the gas was returning to the bottom of the tank
In 1986, BMW changed the design of the tank to have the return line going internally to the top of the tank. This modification resulted to the removal of the return valve.
This is another reason to provide the serial # of your bike.
If I had it, I could right away tell you what type of tank you have.

Cheers

Bert

WB1051301G0042882

I found some service records. Some noticeable things from the last service record I have (fall 1998) are:
Complaint of fueling/cutting out problem (sounds familiar)

They installed: new fuel pressure regulator
Valve adjustment
new crankcase hoses and fuel lines and vacuum hoses
new throttle position sensor
adjusted co emission value
renew throttle butterfly switch

and all the normal spline lube and fluid services.

Odometer was at 21000 then, and is at 27000 now.

Dealer service was $1500! That's more than I paid for the bike!

I was going to say looking at that it would not have been cheap! but having said that, and assuming an honest dealer??, at least you can eliminate those parts out of the equation although it is probably worth checking everything has been tightened properly.

Unfortunately you also have to wonder if that is why it was sold.

phil_mars wrote:I was going to say looking at that it would not have been cheap! but having said that, and assuming an honest dealer??, at least you can eliminate those parts out of the equation although it is probably worth checking everything has been tightened properly.

Unfortunately you also have to wonder if that is why it was sold.

Well it had 6000 miles put on it in 12 years... I think the original owner told me it hadn't been ridden in at least 8 years. When I got it, he said he changed some fluids and put a new battery and plugs in and it wouldnt start. I got it home, it started right up, and I rode it about 5-6 miles before it died and I'm in the spot i'm in now.

Funny I have lost count of the number of threads about K's sitting unloved somewhere for eons and then being purchased so they may live again

And therein lies the problem as lack of use tends to introduce some real nasty issues due to deterioration but I think most of them are fuel related because of the old fuel gumming up the system. Or the Crazy Frog problem of animals nesting in the intake so might be worth pulling that apart just to make sure.

Rubber can also dry out over that period of time so probably worth checking the vacuum lines for cracks etc if not already done.

Have you pulled the fuel pump out and checked it over? And then looked into the fuel well to see how much crap is in there, like water, and more bad fuel? When it pooches out, are you able to immediately pull the fuel line off the fuel rail and determine if there is flow?