Hi Guys, I'm new here but am already loving the mass of information available on the k100 (which I've only owned 3 weeks!)

I have a problem where my injectors are not injecting. I can confirm the following:

• Fuel Pump - Took hose off, squirts fuel with gusto
  
• Injectors - 16 ohms reading, and will squirt under certain conditions.
  
• Water Temperature sensor - Brand new
  
• Fuel Pressure Regulator - Brand new
  
• EFI - Tested ok on another bike.
  
• Air flow meter - Resistances check ok apart from pins 7-5 showing 59 ohms with vane close, but resistance does increase with opening of the vane
  
• Air temperature - resistances check ok.
  
• When starter is pressed pin 9 (EDITED FROM P4) on the EFI reads 8v not 12v
  

The only time I can get the injectors to inject is if I unplug the water temperature sensor, then they will give a big squirt on the press of the starter then again on the release, no squirt while starter is on.

I have not tested the Hall sensor yet, this could be an issue as the first time it broke down was when the engine warmed up and as the the pulse of the injection depends on the readings of the HAll sensor I guess if there is no signal it wont pulse?

I need to re test pins 2, 3 and 9 on the EFI as I couldnt quite figure how test them properly, well pin 9 I missed out.

If anyone is adept with the Jetronic system and might have an idea any advice would be much appciated.

Your are talking about ECU and EFI...but I believe the 1990 rs has a Motronic system. I am right?

From the tests that we did on the MAF, 59 Ohms between pins 7-5 could be a cause of concern.

If you are talking about l-Jetronic system, voltage on pin #4 comes straight from the starter button. Any chances that your starter button is corroded.

Check on the download section, under electrical. There is a good document written by F. Bauer showing how to open and clean your right handlebar switches.

Crazy Frog wrote:

If you are talking about l-Jetronic system, voltage on pin #4 comes straight from the starter button. Any chances that your starter button is corroded.

In addition to the above well worth cleaning the ignition switch contacts and checking the clutch switch resistance along with all earths and "De-Oxiting"? all electrical connections just so all the basic boxes are ticked and you are not going around in ever decreasing circles.

Regards,

Phil

Mine is a 8v LE-Jetronic model. I made a mistake the voltage drop is on pin 9, pin 4 reads 12v fine. Had to double check that with my mate who helped me last nigh.

I just been through the circuit diagram again and I think I will go through as many connections as poss to check contact and resistances. Was thinking of checking the Injection relay just in case it's adding resistance to the line.

Well You already found something flaky on the MAF (59 Ohms between pins 7-5) and now you are finding a voltage drop on pin #9.
this may points your problem toward the MAF
Do you have ignition on the 4 cylinders? If yes, the HALL sensors should be OK.
Remember:
Electronic ignition module pin #7 send ground to the coil of the FI relay as soon as the starter switch is depressed. The ground will stay on after the starter switch is released as long as the Electronic ignition module receives a signal from the Hall sensors.

Please remove the tank and check the connection on the ignition module. Your problem could be as simple as this.

Bert

Ok I managed to find a Jetronic testing box on eBay It informs me
that the Airflow meter and Throttle switch aren't operating correctly.

So I decided to retest the voltages and resistance of all the pins as in
your trouble shooting guide, the results are:

Pin

1. Not tested
   
2. 7v
   
3. 7v
   
4. 8.5v
   
5. 0.6ohms
   
6. n/a
   
7. 7-5=59ohms & 7-8=331ohms
   
8. 8-9 225ohms
   
9. 11.1v
   
10. 2.5kohms
    
11. n/a
    
12. 7.2ohms
    
13. 0.6ohms
    

Instantly I have a major voltage issue at pins 2, 3 and 4. I also have resistance issues on pins 7-5 and 8-9. But the voltage at pin 9 is just below whats required. So if the voltage is pretty much what you might expect at the airflow but drops after it and the idle switch I can only assume either the air flow and/or the idle switch is dragging down the voltage. I shall test between the airflow and idle switch and then short with correct resistance at the airflow to test after the idle.

It's still low at pin 9 so FI relay might be causing contact issues, but not too much it seems. The fule pump is disconnected so that shouldn't be affecting anything.

Pin 4 is also low, I suspect a bad starter relay here so will pull that out and give him a check.

Is there anything else I should be checking?

I just whant to say many thanks for this troubleshooting guide it is massive help.

I am surprised that you measure 2.5 kOhms on 10. From your initial story I would have thought you have a short in your temp. sensor wire. The ECU stops injection/won't start etc if it gets a signal that the bike is too hot. Temp sensor is NTC, so a short in the wire between sensor and ECU could lead to your problem, however you measure OK (about 20C?).
Did you have a look/open up your injection unit? Under the tank directly behind the steering? Some have had issues with water ingress there. Interesting one!

Just a quick answer as i will look at your problem later.
In 1984-1985 it was a recall on the ignition unit as it wasn't waterproof.
As the recalls are valid for only 10 years, you cannot go after BMW.

ReneZ wrote:I am surprised that you measure 2.5 kOhms on 10. From your initial story I would have thought you have a short in your temp. sensor wire. The ECU stops injection/won't start etc if it gets a signal that the bike is too hot. Temp sensor is NTC, so a short in the wire between sensor and ECU could lead to your problem, however you measure OK (about 20C?).
Did you have a look/open up your injection unit? Under the tank directly behind the steering? Some have had issues with water ingress there. Interesting one!

Well origianally I suspected the temp sensor so I replaced it with a new one, then consequently found this forum and the troubleshooting guide with the values needed to test components. So I suspect the old sensor was fine, but hey, a new one can't help and the 2.5kohms is about 17degrees on the chart which was what the outside temp was.

The unit under the tank is the ignition unit, but no I havent opened that up. I've done more testing tonight with a nive Fluke tester, and the readings are more positive. My injection rail is giving 4.4ohms which is fine, and I'm getting 11.5v on the middle pin of the plug to the idle switch when I crank it. I've also still got bad readings on the air flow, so it seems that the idle switch has bad contacts inside, this is hinted by the blue corrosion on the switch plug contacts, so I think water must have got in. It's gonna be a bugger to prise open as it seems to be made of backerlite so i'll probable snap the latches to get inside.

I'm also gonna get a replacement airflow which will hopefully offer the correct resistances.

I've also discovered why I was getting 8.5v at pin 4.......I wasn't closing the clutch, this voltage increased to 11.3v when I pulled the clutch in. Not sure how the electrics work at the starter as the clutch should not allow current to pass when open. But before you say it yes I have been testing the clutch before I delaced it broken down

Hi jwab,
Great measurements by the way most beneficial. A 1990 K100RS should not have an idle switch it has a potentiometer with no idle switch at all nor a wide open throttle switch it is all done by the variable resistor. You also should have 16 valves, AFAIK 1989 was the last 8 Valve so unless you have an 89 or earlier sold in 90 that implies a replacement engine to me. Can you recheck so we know what exactly you have please.
Regards,
K-BIKE

Your measurement re clutch makes sense. There is a start inhibitor arrangement on the bike that you can only start her in neutral. That is arranged for in the speedo (on the basis of a signal from the gearbox indicator print) - the green light. If the speedo doesn't work (no signal from the gearbox switch/faulty print/bad connectors etc.) the other signal it uses is the clutch handle switch. If the speedo doesn't work you can still start if you pull in the clutch.

As you can see on the following schematic, the power feeding the starter button is passing through the gear indicator display.
The clutch switch bypass the the gear indicator and feeds the starter button directly.

Good one Bert, forgot you had it mapped before.

K-BIKE wrote:Hi jwab,
Great measurements by the way most beneficial. A 1990 K100RS should not have an idle switch it has a potentiometer with no idle switch at all nor a wide open throttle switch it is all done by the variable resistor. You also should have 16 valves, AFAIK 1989 was the last 8 Valve so unless you have an 89 or earlier sold in 90 that implies a replacement engine to me. Can you recheck so we know what exactly you have please.
Regards,
K-BIKE

I can confirm I have the 8v model. It is registered as a 1990 but it's had 12 owners and was sold as 29,000miles but then I found out from the ever improving gov direct website that it's actually covered 76,000miles so it was quite possible it was registered late or an old engine put in Que sara sara, we live and learn I guess.

So I'm pretty sure it has the idle switch, or Throttle Position Switch as a supplier calls it.

I measure a strong 12.65v at the battery so I would like to at least keep 12v past the FI relay. It shouldn't offer that much resistance.
It would be great to have the tolerances of the FI computer on it's inputs, I can't believe it demands exact voltages to work properly.

***update****

I've removed both the MAF and the Idle switch. I've cleaned the contacts on the idle switch and now I get a nice 0.1-0.2ohms resistance when the switch is on at both full throttle or closed throttle. Incidently for those who wish to test in future I think pin 2 is full throttle pin 18 is live and pin 3 is closed throttle.

...|2 - 18 - 3|
|full-live-closed|
----------------
| ...................|
..|.. BOCSH ...|
....|........... |
......--------

I've done some more testing on the MAF and although the resistances are low on pins 7-5 I can get it to the correct resistance with some adjustment to the vane, so i'm wandering if its the vane stop which has worn a fraction causing a bad reading. So I'm gonna assemble it tonight and wedge the vane a fraction to see if I can get it to work.

Still not convinced these little changes would prevent the injectors pulsing as so much sonsor information is igonored at startup. Perhaps it's just the strange voltages which causes the EFI unit to get confused?

Do you have the possibility to try another AMM? Some have damaged resistor tracs so the vane doesn't proerly track and the signal is not properly corresponding to the amount of opening of the vane. Can you measure if it gives consistend readings over the opening up of the vane?

Rights so I decided to dismantle the airflow meter! Took the top box off and noticed the carbon track was nicely rutted. No matter I was gett the correct reading when the arm was a fraction forward of it's position, so I unscrewed the arm adjusted it togive 86ohms on pins 7-5. Then screwed it back, took a few goes but it worked, the vane now gives good resistances.

So I put it all back together and tried fireing the bike....no joy, so I decided to take anther look at the hall sensor readings, this time I could use my nice new Fluke meter, and low an behold I was clearly only getting a reading on the press then release of the starter. So I swapped out the hall sensor and checked the meter and got a good fluctuation.

Now the bike runs!!! The problem is it runs very badly, a shit load of grey smoke is pumped out the back and it sounds like it's miss fireing. It won't idle it need to be on the throttle.

So what am I looking at here? I remember when taking the airflow out there was an allan key screw I tried to undo but discoverd that it wasn't attached to the houseing, any idea what it does?

I'll take the injectors out again and see if any muck has got on them, they might not be atomising properly. Apart from the airflow and injectors what else should I be looking for?

Thanks in advance guys this is helpful

First I will say that this answer is available in the download section (K-Bikes How to.pdf).
I have put what is certainly the most comprehensive and complete library of documentation for the K75/K100 available in a single area.
Please read it!

The screw that you tried to remove is the air bypass screw. It is used to adjust the fuel/air mixture ratio at idle.

You can read about it on the Haynes manual page 147. (in the download section)
You normally need a CO2 analyzer to set it properly.


Here's a manual method of setting L-Jetronic K bike fuel injection CO (carbon monoxide) mixture without the need for an exhuast gas analyzer (written by Rob Lentini):
Thoroughly warm the engine.
Remove the rubber plug from the top right corner of the air box, above the engine. Using a 5mm allen, adjust the air flow meter idle air bypass screw under the plug for highest attainable idle speed. This should be about 1-2 turns out from the fully-seated position CW.
Using a Carb Stix mercury manometer or vacuum gages, reset the butterfly bypass screws to resynchronize and establish an idle of 1050 rpm, or about one tach needle width above 1000 rpm.
Now turn the idle air bypass screw CCW (from the top) until rpm is lowered by 50 rpm to 1000, about 4-5 total turns out. (This is called the lean drop method of setting CO, if you don't have an exhaust analyzer.)

Bert

The late great Rob Lentini sadly missed, it was a great loss to the BMW community when he passed away. Fortunately his wisdom lives on via the internet.
Regards,
K-BIKE

Slapped on a second hand airflow meter yesterday. All good now. 130mph test run proved that .

So to cap off my issue.

Bike had corroded idle switch connections, a dead Hall sensor and faulty air flow meter.
In the process of discouvering the problems I replaced:

• Coolant Temperature sensor
  
• Fuel Pressure regulator
  
• Airflow meter
  
• Hall Sensor
  

£157 in parts plus £36 on a Jetronic tester which I'll resell on ebay.

I suspect some fine tuneing is required, will get MPG values and if under 45mpg I'll get tuned, however it doesn't 'sound' bad.

Thanks for the help fellas, and the great technical documentation of this site.