Gas turns off engine after start

[asafl]

Hello to all the genius riders, and thank you for creating this forum.

I have a unique issue with my K100, after visiting the garage and taking a quick wash to look nice and shiny.

I start the bike, all good. I then give the engine some gas - and it shuts down. This is true in first gear as well. It just won't hold gas or give any power other than idle.

With the recommendation of my local garage, we replaced the idle switch to a genuine bosch purchased off ebay (PN purchased 0280120302 -
Genuine Bosch Throttle Position Sensor). It didn't help. The mechanic said he checked everything mechanical and all is in order (fuel pressure, pump working, etc) and stated this is an electrical issue - requesting me to go to the central BMW dealership to "connect to the bike's computer, and reset it".

After calling the dealership, they stated they don't support these bikes and certainly have no "computer" to test the "computer" on a 1986 machine - as it shouldn't have any sophisticated computer to control everything.

I'm desperate, truly. Any help would be appreciated.

Thanks!

[wally.fisher]

Did the bike run well before you washed it? Id suggest cleaning all electrical connectors especially those under the tank and seat.

Sent from my ONEPLUS A5000 using Tapatalk

[asafl]

It ran perfectly fine.

Can you please direct me to a photo/manual of all electrical connectors that require cleaning in your opinion? I have zero experience.

Sorry and thanks.

[Laitch]

Did the bike run well before you washed it? Id suggest cleaning all electrical connectors especially those under the tank and seat.

Can you please direct me to a photo/manual of all electrical connectors that require cleaning in your opinion? I have zero experience.

Such a manual has not been compiled yet, asafi. You have learned that not many mechanic's are ready to tackle K-bike problems; that's the reason sites like this one were created.

The bike has many electrical connectors. Go here todownload the K75/K100 2V manual for your bike. Go here to view diagrams of your bike's components and the cost of them in US dollars.

If you rinsed your bike with a high-pressure stream of water, it's likely water is interfering with complete electrical connections, hence Wally's suggestion.It might just be that a full day or two in Tel Aviv's sun will dry the bike enough to get it running well. In the meantime, here are photos of the locations to which Wally refers. There are other connectors to check under the tank and explanations are here to explain removal of the tank to check them.

The under-seat fuel injection control plug.


The 4-pin under-tank connector on the right side.

[asafl]

Wow. Thanks so much for the detailed reply and the links.

Bike was in the sun for 2 days after the wash and was in the garage for another 2 weeks (not in the sun, but that should suffice in the heat to dry it all out).

I will learn the subject, clean what you stated and see what I can do on my own. Thanks!

Is there a recommended tool kit for self maintenance of the bike?

Thanks again

[Laitch]

I will learn the subject, clean what you stated and see what I can do on my own. Thanks!
Is there a recommended tool kit for self maintenance of the bike?

Because the bike has not run in two weeks, be certain the battery is fully charged.

When you work on electrical connections, it is best to disconnect the battery. The simple way to do that is to disconnect the battery's negative wire that is attached to the transmission on the left side of the bike, usually with a hex screw. Remove the screw; wrap the ring terminal with tape so it does not accidentally contact metal. The favorite electrical cleaner over here is DeoxIT. If that isn't available, use a high quality electronic cleaner. Disconnecting the negative battery cable is also a good way to preserve the battery's charge if the bike isn't going to be ridden for days or weeks.

The bike originally had a tool kit that was stored inside the tail cowl. If that is gone, you'll just build your collection as you go.

[Inge K.]

Check the big hose between the air filter housing and plenum chamber.

if OK, remove the air filter and bottom half of the air filter housing  to get acces to the air flow meter
and check that the vane opens easy and moves freely.

[Scott_]

My be just coincidental that it started after the wash, but how old is the fuel filter..... just because it can make pressure, doesn't mean that it can have adequate flow volume.

[asafl]

Hello all, again.

I've just returned from a business trip and well, still can't start the bike.

The same problem remained, but seem to have worsened now: the bike doesn't even start. When it used to start and stay idle until I increased the RPM and then it'd shut down, now it doesn't even start.

The bike since then has been towed to a professional electrician here, who has examined the problem in detail - checked obvious issues such as fuses, fuel pressure for the pump and strength of plug, and has now concluded, that in "90% probability, the issue is the temperature sensor.

I've looked online and I can get one pretty easily (I don't know the exact PN but maybe you guys can help?).

But what's more worrying is that through digging around online I found out the issue may be the hall effect sensor?

I honestly don't know as I'm neither a mechanic nor an electrician, but would appreciate if you could please help a little bit here.

The bike is connected to an external battery and we have also bypassed the starter, so a high power battery is connected directly to the starter. We try to start it, but it shuts down, giving a very short starter. Click, start for two-three cycles, shuts down. Previously, I had very long starter, even if it didn't start.

Help?

Thanks!

[Insideoriginal]

The ECU only monitors the amount of air coming in, the engine temp, the crankshaft position and ambient temp. The Hall effect sensor monitors the crankshaft position. If it’s not working your bike doesn’t know when to fire the fuel injectors and spark plugs. That can cause it to not run well off idle. Before you replace the sensors, did you replace the spark plugs and ensure you have good fuel? You might want to totally drain your gas tank and replace with high octane  if you are even slightly concerned about the quality of your fuel. Pretty critical starting point.

[asafl]

Thanks for your detailed reply. The spark plugs have been changed and the fuel is only 1.5 months old, but we have put extra fuel in the tank.

When we replaced the plugs, they came out wet (which makes sense), but when we checked the spark with one plug out, the spark seems to weak, like it should only be able to start the fire with the fuel and not really sustain it (that may be an uneducated observation).

[Skunky]

When you press the start button you should be able to hear the fuel pump and see the fuel moving in the tank. If you can not its likely to be the four pin fuel tank connector. They are notorious for failing for no appparent reason. I would suggest opening them clening with a chemical contact cleaner and try again. You should also check and remake the earth connections under the tank while you have it off. If it still doesen't start do the four pin again and again before you start looking anywhere else. It may just start after that.   

[Insideoriginal]

1.5 month old fuel is old. I’d drain and refill to eliminate that as a possibility. Even tiny amounts of water or bad gas can cause a bike to not run. If the spark seems weak, it probably is, fowling plugs is easy and can happen very quickly. Swap them out too. If the plugs are firing it’s probably not the crank position sensor. I’ve worked on a number of these bikes and it’s usually something really simple that keeps them from running. Don’t go to far down some rabbit hole without fixing the obvious things.

Speaking of obvious things, the rubber intake manifolds and rubber nipples on the throttle bodies go bad and the nipples will crack and fall off, vacuum leaks, I’ve found, are a top ten cause for k bikes to not run or not run properly.