k100 wont run past idle

[raew]

I have just purchased a K100 (1991yr) that has not run for a year. It will start and run at idle, but will not rev past 1400rpm, where it just cuts out. While running at idle the engine sounds good.

 

Fuel has all been replaced (due to it all leaking out of a hole in the tank initially).

 

New plugs been used.

 

Any ideas where I should look?

[BMT]

This symptom rang a bell, but when I looked it up it's slightly different. Might be worth a look, though.

 

Motobins Technical Tips

 

There's a throttle switch to shut off fuel above fast idle, but apparently it's effective above 3000 rpm.

[bmwmick]

I'd replace the fuel filter and check the pressure on the injector rail. You should have about 36psi there with the engine running.

 

Mick

[RFW]

This CANNOT be a fuel filter problem as another poster has mentioned. The fuel pump on this bike (I know, because I have a K100 and know the fuel system intimately) pumps a constant volume of fuel, more than the motor will ever use, around a "ring", past the injectors (which tap fuel off this ring), and back through a pressure regulator to the tank.

 

The fuel filter and pump, has no way of knowing what RPM the motor is turning.

 

As another poster has stated, the problem is almost certainly the switch that signals the injection system to cut the fuel off when the throttle is closed.

 

The system works like this... At higher RPM, when you close the throttle, the injection system senses the closed switch and cuts off all fuel. As you coast down to 2000 RPM, the system overrides the closed throttle switch and starts fuel flow again to ensure the motor does not stall.

 

Your problem is likely NOT a defective switch, however. Microswitches are, after all, very reliable. The problem is likely someone setting the switch incorrectly, and the switch is closed all the time.

 

The switch is located at the rear of the shaft that rotates all 4 butterflies. It is a black plastic box about an inch square and 3/8" thick with a cable connector at the top.

 

First, put your ear close to it (bike not ruinning) and listen for a click as you JUST open the throttle. If you hear none, loosen the 2 screws and rotate the thing until you DO hear this click JUST as the throttle closes.

 

If that does not help, unplug the connector and see if the bike runs normally. If so, the switch is shot. If not, you need to check the contact in the connector (that leads into the wiring harness) to see if there is a wiring harness short. That is more difficult and requires a bit of technical knowledge, an Ohmmeter, and a wiring diagram. PM me if you need instructions on this.

[raew]

Thanks for all the advice.

Nick, as you have said, only above 3000rpm, so dismissed this.

 

Bob, your advice sounded the most likely. But switch does click, and removing the connector did not change anything.

 

Mick, while I dont think it is fuel feed related, I am going to change the filter.

 

What I did find out was when starting from cold.

No throttle, half choke, short press on starter button; engine fired and ran (smoothly). Revs could be controlled upto 3000rpm and down to 1000rpm by movement of the choke, but any movement of the throttle cut the engine.

 

Once the engine was warm, and choke no longer needed the bike would not start and run as previously mentioned in the first post, but did not want to try this for too long as previously we have flooded the engine and fuel leaked out of exhaust drain hole.

 

Bob your explanation seemed to be exactly what would cause the problem but with the cable disconnected from the sensor the fault was still present, am I right in thinking this rules out a problem with this sensor?

 

Thanks, and any more help much appreciated.

[bmwmick]

In addition to the above, you could have a failing coolant temperature sensor. They have been known to cause the problem you are seeing.

 

If your fuel pressure is good (above 36psi) I would clean and reseat ALL the injection control unit connectors. The one from the Air Meter especially. Then change the temp sensor if your problems continue.

 

I had a loose hose clamp (from the factory) on my K-bike at one time and the symptoms were just like yours.....it would idle but not take ANY throttle. The fact that your's changes when the engine is warm leads me to suspect the temp sensor.

Item#15 here: http://tinyurl.com/rf38e

 

Mick

[raew]

Thanks Mick

 

Fuel filter has been changed now. Fault still the same.

 

Fuel pumping through ok, tested and fuel flew approx 9ft.

 

Not sure about your temp sensor. As when I said it ran ok on choke that was only for approx 30 secs, not long enough for the engine to have warmed up, but long enough for the choke no longer to be used.

 

I am now getting to the point were I do not want to keep changing things it might be and am thinking it might be time to take it to a dealer.

 

A bit of history; this bike did not cost me a lot as it had been sitting outside someones house for over a year not running, I bought it cheap and have a limit as to how much I wish to spend, if its going to be too much its not worth it and would be better off buying one thats running.

[Bruce C]

One thing the "choke" is not a choke as we know one. It is simply a high idle cable going directly to the throttle plate bar.

The bike has been sitting for over a year. Is there any way for you to drain the tank, add about 6oz. of fuel injector cleaner and refill?

[Dennis Andress]

If your bike is a 16 valve K100 then its worth putting something into, those bikes rock!

 

What you called the choke is not really a choke at all but a fast idle adjuster for use while the bike warms. The computer does all the fuel enrichening work on its own. What you described - the bike runs okay for a short while when cold - leads me to think its running rich, very rich.

 

Changing the temp sensor on my 91 KRS made a huge improvement but I don't think its the answer for your problem. If it were my bike I'd check for a drippy fuel injector. Its fairly common for them to not close completely when dirty or worn. Pull off the fuel rail with the injectors and fuel lines attached and put a small piece of cardboard under the injectors to act as drip indicator. Then turn the key on and off slowly a few times to energize the fuel pump - don't crank the engine. If there a signs of fuel on the cardboard you've got a bad injector.

 

If the problem isn't an injector then I'd look at the fuel pressure regulator. Perhaps its stuck and isn't relieving pressure when the throttle is opened.

[BMT]

Okay, a couple of other things.

 

First, double-check the throttle closed switch with a meter, to see that it is changing state between throttle closed and opening. ISTR that it operates the other way round -- so disconnecting the wiring will always be faulty.

 

When started cold and the engine begins to warm, what is the smell of the exhaust gas like? (Beware of excess fume inhalation, of course.) Does it smell rich or normal? What about as the temperature rises? Any change? For the engine to run cold, but not hot, would suggest hopelessly rich mixture.

 

Are all four throttles really opening?

 

Check condition of rubber components around the throttle bodies.

 

How is the throttle position passed to the FI controller? Is it a potentiometer on the throttle spindle? (Bob, you probably know that one? I never had to go there with my K!) What I'm getting at, is that the throttles may be opening, but the FI doesn't know about it, so much more air but no extra fuel.

 

Final possibility is the airflow sensor (inside the airbox, above the filter element). It's a vane attached to a position potentiometer and can stick.

 

Oh, one more. It wouldn't be the first ignition coil to work when cold and fail when hot or at higher revs.

 

Whatever it is, it's almost certainly something common to all four cylinders. They'll usually get you home as long as two or more are working </voice of experience>.

 

Bon courage, as they say in these parts!

[Bobmws]

Thanks Mick

 

Fuel filter has been changed now. Fault still the same.

 

Fuel pumping through ok, tested and fuel flew approx 9ft.

 

Not sure about your temp sensor. As when I said it ran ok on choke that was only for approx 30 secs, not long enough for the engine to have warmed up, but long enough for the choke no longer to be used.

 

I am now getting to the point were I do not want to keep changing things it might be and am thinking it might be time to take it to a dealer.

 

A bit of history; this bike did not cost me a lot as it had been sitting outside someones house for over a year not running, I bought it cheap and have a limit as to how much I wish to spend, if its going to be too much its not worth it and would be better off buying one thats running.

 

Given this history, pull the air cleaner and see if you don't have a mouse nest blocking the intake. Won't be the first time this has happened!

[RFW]

First, double-check the throttle closed switch with a meter, to see that it is changing state between throttle closed and opening. ISTR that it operates the other way round -- so disconnecting the wiring will always be faulty.

The switch is normally open, and closes when the throttle closes. I checked. Also, if you can hear a click, then it is impossible that the switch could be shorting closed. So it appears that the switch is not the problem.

 

As an aside, this switch housing contains two switches; the Closed Throttle switch and a Wide Open Throttle switch (the latter is not a microswitch and does not click).

 

Are all four throttles really opening?

Not much choice there! They are all linked together mechanically and it is not possible that one or more cannot open.

 

How is the throttle position passed to the FI controller? Is it a potentiometer on the throttle spindle? (Bob, you probably know that one? I never had to go there with my K!)

The bike uses an LE Jetronic injection system. As with nearly any injection system, throttle position itself is not sensed. Instead, inlet air volume is, using a big die cast flap that is pushed further open as more air is inhaled. The flap position is sensed by a pot. The low volume of air used at idle is bypassed around this flap, and is adjustable using an allen key, which is used to set idle mixture.

 

What I'm getting at, is that the throttles may be opening, but the FI doesn't know about it, so much more air but no extra fuel.

This is not directly possible because (see above) the FI system doesn't get any info on throttle position in the first place.

 

BUT... it is possible that the FI system's air volume sensor flap is stuck as a result of long term disuse.

 

The sensor is a big honking thing that is located above the air filter in the same plastic housing on top of the motor.

 

One can test to see it is not stuck by removing the air filter, and sticking your finger into the rectangular inlet opening in the diecast metal sensor assembly. Try moving the flap inside. It should feeely be able to be moved. If it is stuck, or some resistance to motion is felt, then opening the throttle will probably kill the motor, since the mixture will be WAY off (because the FI system doesn't "know" more air is trying to be sucked into the motor).

 

Final possibility is the airflow sensor (inside the airbox, above the filter element). It's a vane attached to a position potentiometer and can stick.

Ooops! Didn't realize you'd covered that already!

 

Oh, one more. It wouldn't be the first ignition coil to work when cold and fail when hot or at higher revs.

But there are two coils. Even with one dead, the other would still work, so the motor wouldn't die; it would just stop running on 2 of its cylinders.

 

One other possibility is that this bike sat for so long, there may be varnish in the injectors. They may spray well enough for idle, but cause a problem with increasing load. Pull one out and watch the spray pattern when you briefly start the motor. If it sprays all cockeyed, this will be a problem.

 

Finally, it is important to try to verify if this is a fuel or an electrical issue. Start the bike and VERY slowly open the throttle so the revs start to climb SLOWLY. Take note of the RPM at which it starts to cut out.

 

Now get on the bike (still on the main stand) and apply the rear brake a little. Try the same thing as above. This time the load of the rear brake will require a larger throttle opening. Again, with the motor under the rear brake load, and the revs slowly increasing, take note of the RPM where the motor runs into trouble.

 

If in each of the above tests, the problem started at about the same RPM, your problem is PURELY rev-related, and not related to load. This implies an electrical problem (possibly with the ignition contoller).

 

If the loaded test shows the problem occurs at a lower RPM, then it is problably fuel system related (air volume sensor stuck, injector problem, and so on).

[duckbubbles]

A '91 K100RS should be a 16 valve engine with Motronic F.I., but with no O2 sensor. Maybe it's the throttle position switch.

 

Frank

[RFW]

A '91 K100RS should be a 16 valve engine with Motronic F.I., but with no O2 sensor. Maybe it's the throttle position switch.

 

OK. Good point. Didn't know they switched to Motronic.

[bmwmick]

A '91 K100RS should be a 16 valve engine with Motronic F.I., but with no O2 sensor. Maybe it's the throttle position switch.

 

OK. Good point. Didn't know they switched to Motronic.

 

If we had the last 7 digits of the VIN we could ALL be of more help. : ))

 

Mick

[BMT]

If we had the last 7 digits of the VIN we could ALL be of more help.

Better still if we were standing around the bike! Can we check our diaries, please?

[nldaniel]

yeah that would be great.. twenty-odd people standing around, pointing at stuff.. check that check this, no that's the wrong thing to check! OH YEAH! YEAH! OH YEAH!..

 

seriously, seeing K100 everybody (myself included) thought 8V engine, with the older injection system.

 

so, starting over, I think it would be wise to check the motronic for stored faults. since you pulled the plug from the throttle position switch it shoud have at least one.

 

for a write up, see http://www.geocities.com/fwarner_au/mc_things/K_fuel_injection.html

 

check the codes, clear the codes (or disconnect the motronic for a 5 minutes) and recheck to see if they reappear

 

oh yeah, crank the engine a moment, without starting (just a tap) before reading the codes, this prevents the hall sensor codes from popping up.

 

HTH Daniël

[RFW]

seriously, seeing K100 everybody (myself included) thought 8V engine, with the older injection system.

Exactly. But as a general thought, I'll wager that this bike was running OK before it was stored for so long. So I suggest looking for things that could have happened as a result of the storage.

 

Some suggestions are varnish buildup in the injectors, or moisture in the electronics or sensors, or corrosion causing problems ...that sort of thing. The electronics themselves do not fail just because they were sitting a long time.

[raew]

JOb sorted, she's now a runner.

 

While surfing BMW sites found this site

http://www.moto-one.com.au/performance/K1K100RS4V.html

with this info

" We had pretty much come to the end with the only variable I hadn’t ruled out being the ECU. I don’t usually suspect ECUs of this kind of problem, as the bike was just running very lean. Would start and idle fine, but die when the throttle was opened. ECU problems are usually a bit more dramatic, but all the usual suspects had passed examination so it needed to be cleared. The only problem was getting an ECU to try."

 

Managed to get a secondhand ECU, installed, and first press fired up and ran very smooth.

 

Now its a runner, just to sort out rattley cam chain, and leaking fork seals.

 

Thanks to everybody for the help.

[Dennis Andress]

Good find. Got pictures??

 

Now its a runner, just to sort out rattley cam chain, and leaking fork seals.

 

If this is an RS the forks may need more then just seals. I changed mine three times before I figured out that the top and bottom bushings in the sliders were worn too. My experience says to change the seals, wipers, and bushings so everything is happy together.

 

The cam chain tensioner works off of oil pressure so check it out right away. You will probably need to take off the valve cover and front chain cover to inspect the chain guides and the tensioner.

[RFW]

Managed to get a secondhand ECU, installed, and first press fired up and ran very smooth.

I'll bet that if you look inside the ECU, you'll find corrosion or water damage as a result of a year spent outside. If so, that is something easily fixed if necessary.

[tonycombs]

It sounds to me like the injection brain(Injection Control Unit), mine did the same thing, you can check all the sensor's you like, but if you can get your friendly dealer to let you hook up a working one, you will know immediately.

They are not cheap, but you can get used ones.

[NeverWashItJim]

If this is an RS the forks may need more then just seals. I changed mine three times before I figured out that the top and bottom bushings in the sliders were worn too. My experience says to change the seals, wipers, and bushings so everything is happy together.

Hey Dennis -- thanks for this tip. I had new seals put in last summer on my '92 RS (I'm too much of a wuss to do my own work) and they've been weeping ever since. I went back a few times, but the problem was intermittent, so I always got a brush off answer. If I decide to keep the bike, I now know how to fix it.