Hello all,

I've been working on this '87 K100 RS since I purchased it in January. I've found a lot of people's threads helpful in getting to where I am now, but I need some help diagnosing a current issue that's been causing me plenty of headaches as I am an inexperienced mechanic.

The primary issue of the bike when I purchased it was a major oil/water pump leak, which required a replacement of the entire unit (the last owner installed a k1000 pump and the seals broke). The bike then moved and rode just fine with only a few leaks as I reinstalled all of the gaskets and rubber bits that held the engine cases together. However, during the first ride I stalled the bike during gear shifts (I am also an inexperienced rider) and since recharging the battery it has not started. I replaced the throttle housing tubes (everything connecting the airbox to the engine) because they had all sorts of holes in them, but the starting issue has not changed.

When pushing the starter button, the engine cranks enthusiastically but does not turn over. Giving it choke only changes the rhythm of cranking as far as I can tell. The fuel pump does make noise. The spark plugs do give spark but when I pull them after a long attempt they are a little wet. One time, when starting, the exhaust flooded with fuel, which to me indicates either a pressure issue or a temperature sensor issue. I took a look at the temp sensor and it did have corrosion on the outside, but it still confuses me why the bike started so easily prior to the stall and does not afterwards.

Apologies for the long post, but I have spent a long time working on it and am ready to ride! my local parts dealer certainly will be happy to work on it... but if a little cleaning or wiggling of wires gets it to go I would be happy to hold off on the pricy visit.

Any advice on what to check is appreciated.

If the temperature sensor is dodgy you can get it to fire by removing the fuel injection fuse No 6 marked Kraffstoppe or disconnecting the fuel pump at the plug. Doing this it will allow it to run on the residual fuel in the combustion chamber until it is burnt off. You can keep it running by reconnecting power to the pump before it completely dies. You will need to manipulate the throttle in order  to keep it running, and it helps to have a second person to replace the fuse or reconnect the pump. Never use thread tape or sealant on the sensor threads as the sensor requires earthing. The corrosion can build up gradually overtime until it becomes an intermittent problem or just fails.
Regards Martin.

vttownie wrote:The primary issue of the bike when I purchased it was a major oil/water pump leak, which required a replacement of the entire unit (the last owner installed a k1000 pump and the seals broke).

I replaced the throttle housing tubes (everything connecting the airbox to the engine) because they had all sorts of holes in them, but the starting issue has not changed.

If by K1000 you meant K1100, the pumps are backward-compatible among Brick models.

Did you replace the z-tube along with the other tubes connecting the airbox to the engine? Have you checked the air intake snorkel for obstruction, the condition of the air filter, the condition of the airbox beneath the air filter to be certain it hasn't become a rodent hotel blocking airflow, and the electrical connection to the air flow meter to be certain it isn't loose?

Have you checked integrity of the fuel tank hose connections and the hoses themselves and changed the fuel filter? The pump makes noise but is it actually pumping?

Have you been consulting the electronic fuel injection troubleshooting guide in the site's Portal? 

Your local parts dealer/service center might do all that then charge you for it. If you do it first, you might discover the problem, pay yourself and have kebab in Burlington with the proceeds.

You wrote: "When pushing the starter button, the engine cranks enthusiastically but does not turn over." I guess you meant that the engine turns over but will not fire up.


I would check the injectors to see if they are firing. Take a long screwdriver, place the bit end against an injector and the handle end against your ear. Crank the engine. If you hear regular clicking sound the injectors are firing. I keyed into your sentence where you said you cranked for a bit and then pulled plugs and they were a little wet. I'd expect them to be drenched. i suspect a connection problem to the ECU under the seat.

You are aware you must have a neutral light showing or else pull the clutch lever [it has a switch that must ber working] in order to get it to start.

The Fuel Injection Control Unit [FICU] under the seat is very high on the suspect list for poor connections. Clean off the pins on it and reseat the plug.

If you RS has a temperature gauge it has 2 temperature sensors. One is on the pump you mentioned. That one is for the gauge only and has no other function. The sensor for the engine management system, cooling fan and warning light is in behind the radiator. [Just checking]. If that one has a poor electrical connection it may send an overheat signal and that inhibits a start too.

Also, as you are on some of these jobs, check out the fan and that it works ok. The bearings in them give out and they can seize.

MartinW wrote:If the temperature sensor is dodgy you can get it to fire by removing the fuel injection fuse No 6 marked Kraffstoppe or disconnecting the fuel pump at the plug. Doing this it will allow it to run on the residual fuel in the combustion chamber until it is burnt off. You can keep it running by reconnecting power to the pump before it completely dies. You will need to manipulate the throttle in order  to keep it running, and it helps to have a second person to replace the fuse or reconnect the pump. Never use thread tape or sealant on the sensor threads as the sensor requires earthing. The corrosion can build up gradually overtime until it becomes an intermittent problem or just fails.
Regards Martin.

I gave this trick a try and it did as you said, started kicking to life, didn't quite get the timing right on the throttle but glad to know this works and glad to know the temperature sensor is a good start. Thanks, Martin!

Laitch wrote:

vttownie wrote:The primary issue of the bike when I purchased it was a major oil/water pump leak, which required a replacement of the entire unit (the last owner installed a k1000 pump and the seals broke).

I replaced the throttle housing tubes (everything connecting the airbox to the engine) because they had all sorts of holes in them, but the starting issue has not changed.

If by K1000 you meant K1100, the pumps are backward-compatible among Brick models.

Did you replace the z-tube along with the other tubes connecting the airbox to the engine? Have you checked the air intake snorkel for obstruction, the condition of the air filter, the condition of the airbox beneath the air filter to be certain it hasn't become a rodent hotel blocking airflow, and the electrical connection to the air flow meter to be certain it isn't loose?

Have you checked integrity of the fuel tank hose connections and the hoses themselves and changed the fuel filter? The pump makes noise but is it actually pumping?

Have you been consulting the electronic fuel injection troubleshooting guide in the site's Portal? 

Your local parts dealer/service center might do all that then charge you for it. If you do it first, you might discover the problem, pay yourself and have kebab in Burlington with the proceeds.

I did mean K1100, thanks. One of the parts guys at Frank's in Essex seemed apprehensive about using K1100 pumps on these bikes. Since I had a spare K100 pump laying around that wasn't pitted we fixed the seals on that and put it on this bike.

I checked the integrity of the Z-tube and other air components for the bike in my update of the throttle intake tubes. During that time all fuel hoses were replaced, though I may look over those hoses to make sure I tightened them all down properly so the system can build proper pressure. 

I'll be digging in deeper into the fuel injection guide as I prepare to clean and inspect all these old connections.

92KK 84WW Olaf wrote:You are aware you must have a neutral light showing or else pull the clutch lever [it has a switch that must ber working] in order to get it to start.

The Fuel Injection Control Unit [FICU] under the seat is very high on the suspect list for poor connections. Clean off the pins on it and reseat the plug.

If you RS has a temperature gauge it has 2 temperature sensors. One is on the pump you mentioned. That one is for the gauge only and has no other function. The sensor for the engine management system, cooling fan and warning light is in behind the radiator. [Just checking]. If that one has a poor electrical connection it may send an overheat signal and that inhibits a start too.

Also, as you are on some of these jobs, check out the fan and that it works ok. The bearings in them give out and they can seize.

Indeed. Bike's in neutral and I did try with the clutch lever pulled to no change.

I'll be looking at the FICU to make sure it's not the culprit. I did the old IT trick of unplugging/plugging back in again but unfortunately no such luck. I'll give the pins a good cleaning regardless.

If I understand your point about the temperature sensor, it's that I don't need to worry about the connection under the pump and instead worry about the plug under the radiator. That one has gunky blue corrosion all around it, so it needs a good cleaning and possibly a replacement. When the bike is set to ignition the temp sensor does read all the way to the right, though as I understand it that might not mean anything.

I'll take a look at the fan as well.

vttownie wrote: Since I had a spare K100 pump laying around that wasn't pitted we fixed the seals on that and put it on this bike.

Did that "we" fixing the seals include you, or was it just the mechanic and maybe the parts guy? Did this spare pump that was laying around come with your first motorcycle?

You're an inexperienced rider and an inexperienced mechanic by your own admission. You should consider sitting down and reading this guide from the site's Portal slowly from beginning to end. Because the coolant temperature sensor seems to be an item of interest, consider reviewing its function and testing procedure in the guide. If you've already done that, a second review could be helpful.

The challenges you're experiencing are not unusual with these aging units, especially those that haven't been ridden much or have been neglected for years. An orderly approach to troubleshooting without allowing assumptions to divert focus will make enjoyable riding happen sooner.

Laitch wrote:

vttownie wrote: Since I had a spare K100 pump laying around that wasn't pitted we fixed the seals on that and put it on this bike.

Did that "we" fixing the seals include you, or was it just the mechanic and maybe the parts guy? Did this spare pump that was laying around come with your first motorcycle?

You're an inexperienced rider and an inexperienced mechanic by your own admission. You should consider sitting down and reading this guide from the site's Portal slowly from beginning to end. Because the coolant temperature sensor seems to be an item of interest, consider reviewing its function and testing procedure in the guide. If you've already done that, a second review could be helpful.

The challenges you're experiencing are not unusual with these aging units, especially those that haven't been ridden much or have been neglected for years. An orderly approach to troubleshooting without allowing assumptions to divert focus will make enjoyable riding happen sooner.

I had brought a K100 pump from a separate K100 engine I had purchased with the sale of this bike. I brought it to the local BMW mechanic to fit the seals and clean the pump.
Thanks a lot for the advice. I'll work through the troubleshooting guide and report back if the bike gets moving again.

I bought a cheap $10.00 Au digital temperature sensor off a local electronics store boiled up two cups of water Make a cup of tea with one hang the sensor probe in the other with a multimeter connected to it and set on Ohms insert the thermometer and take and note the readings as the water cools. You need to measure between the pins and the body of the sensor. Cleaning the threads and the connecting pins can sometimes fix a dodgy sensor. When refitting never use thread sealant, thread tape and always use a copper or aluminium washer not plastic or fibre to seal the sensor. If buying a new sensor make sure it is correct for your bike 8v and 16v look the same but are not interchangeable. 
Regards Martin.

Quick update - took a deeper look into the voltage readings for the fuel system and cleaned all my plugs as me and another set of hands gave the K100 a lookover. Found out that no, to Laitch's comment, that the pump was not pumping while seated in the tank, though once we took it out to inspect further could get it to pump outside of the tank using a battery. Attempted to clear the pressure regulator system with air and it did not change the fact the bike was not building pressure. The rubber seating on the pump still had integrity, and the inside of the tank was clean, but a change of fuel filter may be on the horizon. 

Other things I could test for? What would prevent fuel being sent from the pump to the injectors?

Thanks again all.

I am going to assume you have the pump running and putting out fuel when installed in the tank and that it isn't getting from the pump to the injector rail.  Get down to your local NAPA store and grab an 8032 NAPA Gold filter for 7-8 bucks.  If you don't know for sure when your filter was new, it probably came with the bike almost 30 years ago.

Don't use the fuel line that comes with the filter.  It is not designed for immersion.  Use the old stuff unless it's really broken down.

vttownie wrote:What would prevent fuel being sent from the pump to the injectors?

A clogged pump inlet, a faulty pump, a faulty electrical connection to the pump, collapsed fuel lines, disconnected fuel lines, and empty fuel tank. If fuel under pressure has reached injectors with clogged nozzles, no fuel would enter the combustion chambers.

Draw conclusions from your test of fuel flowing from the tank before moving on to something else. 

Once fuel is flowing to the injector rail, test its pressure by getting a loaner fuel pressure tester from NAPA. you'll need a credit card or a couple hundred dollars in cash maybe but that would just be a refundable security deposit. Use doesn't cost anything and instructions for its use are in the Troubleshooting the EFI guide located in the Tech Page, the access to which is located in this site's Portal.

vttownie wrote:Quick update - took a deeper look into the voltage readings for the fuel system and cleaned all my plugs as me and another set of hands gave the K100 a lookover. Found out that no, to Laitch's comment, that the pump was not pumping while seated in the tank, though once we took it out to inspect further could get it to pump outside of the tank using a battery. Attempted to clear the pressure regulator system with air and it did not change the fact the bike was not building pressure. The rubber seating on the pump still had integrity, and the inside of the tank was clean, but a change of fuel filter may be on the horizon. 

Other things I could test for? What would prevent fuel being sent from the pump to the injectors?

Thanks again all.

Run that pump test out of the tank from the plug that plugs into the tank and see if the pump works. That will tell you if power is getting to the tank but not beyond it. The plug that plugs into the tank can also give trouble due to internal cable breaks if a previous owner tried pulling the tank without disconnecting it first.

Thanks all. This line of inquiry may have come up with a solution. 

I tried a few other tests with the pump outside of the tank, with a battery and with the connecting wires. At first, I thought that it wasn't running inside of the tank because it wasn't getting power through the fuel level sensor, but that was wrong. Power from the wires read out at 12v and the pump would turn on with a push of the starter, but still wasn't pulling any fuel. Even tried submerging it in a can of fuel per other's tests but it wouldn't push anything through. Tried reversing the polarity to see if gunk would come out but no change, just a weak activation through and through. Perhaps there is a blockage inside of the pump preventing fuel to pull, and what came out earlier was old fuel sitting in the pump line. 

I also removed the fuel filter and that too was full of old ish fuel. I'm thinking of doing a full replacement of pump, lines and filter. I know there's a lot of inexpensive replacement options in the other threads so I will take a look through those and report later when I get to transplanting this thing's heart.

I forgot to mention that we did do a pressure test when I got my cousin over to help out. It didn't budge at all. I'll bring him over again with his gauge when I do my replacement.

All these gas fumes make me want to sit down with a nice whiskey.

vttownie wrote:Thanks all. This line of inquiry may have come up with a solution. 

I tried a few other tests with the pump outside of the tank, with a battery and with the connecting wires. At first, I thought that it wasn't running inside of the tank because it wasn't getting power through the fuel level sensor, but that was wrong. Power from the wires read out at 12v and the pump would turn on with a push of the starter, but still wasn't pulling any fuel. Even tried submerging it in a can of fuel per other's tests but it wouldn't push anything through. Tried reversing the polarity to see if gunk would come out but no change, just a weak activation through and through. Perhaps there is a blockage inside of the pump preventing fuel to pull, and what came out earlier was old fuel sitting in the pump line. 

I also removed the fuel filter and that too was full of old ish fuel. I'm thinking of doing a full replacement of pump, lines and filter. I know there's a lot of inexpensive replacement options in the other threads so I will take a look through those and report later when I get to transplanting this thing's heart.

I forgot to mention that we did do a pressure test when I got my cousin over to help out. It didn't budge at all. I'll bring him over again with his gauge when I do my replacement.

All these gas fumes make me want to sit down with a nice whiskey.

Replacing the pump fixed the no start issue! However, when idling, rolling on the throttle kills the engine. Also running into an issue where the starter motor won't turn on when I press the starter button. Going to let the bike charge and add more gas, see where that takes me.

Thanks everyone!

Hey all,

Since I had run across this issue, I have taken these steps:

- Cleaned all relays 
- Replaced all fuel lines to OEM standard (paid the BMW premium)
- Made sure all lines were tight and snug against components
- Tested fuel pressure regulator
- Cleaned throttle sensor

So while I was testing all of the components, I realized that the throttle sensor was corroded - something that my local mechanic told me is often the issue when the engine switches from the idle computer to the throttle computer. Cleaning all electronics really does help figure out the source of many problems.

Now, the bike starts and runs quite well. I suppose the main issue was fuel delivery and throttle detection, though it may not be the only source.

Now, the bike runs well, but exhaust runs heavy out of any pore on the bike. May be an entirely unrelated issue.