Hi all,

I couldn't decide between 'Engine and transmission' or 'Electrical' apologies if this is the wrong category!

Mechanically the bike appears to be fine. The engine compression is good at around 160 - 170psi per cylinder. Starter motor cranks the engine as expected. Fuel is pumped around the system and all the injectors fire. Spark plugs, well, spark.

We've replaced:

1. The battery
   
2. Spark plugs
   
3. Starter relay
   
4. Air filter
   
5. Fuel filter
   
6. Fuel pump (We tried to use it and it shorted. Smoke coming out of the fuel tank! fun stuff)
   
7. A few fuses
   
8. A few relays
   
9. Injectors (replaced due to a mistake, but got them cheap)
   

We've repaired massive chunks of the main (non-engine) loom. Previous owner/s cut tons of wires. I don't believe that this will stop it from starting.

The ECU is reporting 1133 which should be the lower hall sensor. Testing it resulted in positive results, the voltage drops to 0v when passing metal through. One minor discrepancy was that one consumed 0.001ma compared to 0.002ma.

CO pot reads around 500ohm.

All the fuses are fine.

It randomly catches/starts for a second or two when spraying easy start into the air-intake. When we try to start the bike the choke is fully engaged as is the clutch. We've tried adding some throttle to no avail.

Honestly at a loss as to what to do next. Thanks for your time!

plug leads on the correct plugs order ?

If it runs with easy start, then I'd consider fuel starvation. Are you able to check fuel pressure? Or as a an alternative, remove the fuel rail and injectors and fire them onto paper towel to check adequate spray*

*I'm assuming (always a mistake) that you can do this with a 4v, same as you can with a 2v.

th2000125 wrote:The ECU is reporting 1133 which should be the lower hall sensor. Testing it resulted in positive results, the voltage drops to 0v when passing metal through. One minor discrepancy was that one consumed 0.001ma compared to 0.002ma.

It randomly catches/starts for a second or two when spraying easy start into the air-intake. When we try to start the bike the choke is fully engaged as is the clutch. We've tried adding some throttle to no avail.

Honestly at a loss as to what to do next. Thanks for your time!

What is the voltage at the sensor before it drops to 0V?
Are the spark plug electrodes wet after starting attempts?
When the key is turned to On, does the fuel pump make a noise then shut off?
What is your source for the 0.002ma value?

Hi all,

Thanks for all your replies. Sorry for the delay, I wanted to look at the bike again with the feedback.

firstle wrote:
plug leads on the correct plugs order ?

The leads won't reach each other in another configuration.

Suzi Q wrote:
If it runs with easy start, then I'd consider fuel starvation. Are you able to check fuel pressure? Or as a an alternative, remove the fuel rail and injectors and fire them onto paper towel to check adequate spray*

*I'm assuming (always a mistake) that you can do this with a 4v, same as you can with a 2v.

So we tested them all externally with a bench power supply and never in circuit. Fuel rail is getting fuel but this has lead to the discovery that the injectors new or old do not actually open when the starter is triggered. Not sure why we didn't look here sooner.

Laitch wrote:What is the voltage at the sensor before it drops to 0V?
Are the spark plug electrodes wet after starting attempts?
When the key is turned to On, does the fuel pump make a noise then shut off?
What is your source for the 0.002ma value?

1. I'm afraid I don't remember, I applied 12 volts and the analogue voltmeter went up to the same value each on both sensors.
   
2. No. Sadly this and a previous reply lead to the discovery that the injectors are not running.
   
3. Again, no, we were bypassing the pump as the previous owner had too. We discovered that the wires going up to the start button had shorted, after replacing them, no luck still.
   
4. My bench power supply, it was reading 0.009ma for both.
   

Thanks again all for your help!

So, we now have a place to start again but no idea why the pump isn't being initialized or the injectors. I have read that they will not start until the fuel relay does but why wouldn't it start? after some digging I am still at a loss.

th2000125 wrote:So, we now have a place to start again but no idea why the pump isn't being initialized or the injectors. I have read that they will not start until the fuel relay does but why wouldn't it start? after some digging I am still at a loss.

Some of your replies are difficult to understand. Initially you wrote,"Fuel is pumped around the system and all the injectors fire." It is unclear to me if that was before or after you replaced the fuel pump.

When asked if you had verified the spark plug leads were connected to the correct coils, you answered that they couldn't be connected any other way. That doesn't answer the question unless you traced each wire to its coil connection, verifying that plugs 1 and 4 were connected to coil #1 and plugs 2 and 3 were connected to coil #2. Is that what you did?

Your Brick was manufactured with a safety switch connected to its side stand (prop stand). The Motronic fuel relay is involved in both running the pump and opening the injectors. You need to verify that the side stand safety switch is making the connection to the relay so the fuel system has the potential to operate regardless of whether you are using the side stand. If the Motronic fuel relay is faulty if might affect both fuel pump operation and fuel injector operation. Below are extracts from the K100RS/K1 riders handbook and a diagram of the 4V K1/100RS starting path from the Motronic 2.1/2.2 training manual.

Laitch wrote:

th2000125 wrote:So, we now have a place to start again but no idea why the pump isn't being initialized or the injectors. I have read that they will not start until the fuel relay does but why wouldn't it start? after some digging I am still at a loss.

Some of your replies are difficult to understand. Initially you wrote,"Fuel is pumped around the system and all the injectors fire." It is unclear to me if that was before or after you replaced the fuel pump.

When asked if you had verified the spark plug leads were connected to the correct coils, you answered that they couldn't be connected any other way. That doesn't answer the question unless you traced each wire to its coil connection, verifying that plugs 1 and 4 were connected to coil #1 and plugs 2 and 3 were connected to coil #2. Is that what you did?

Your Brick was manufactured with a safety switch connected to its side stand (prop stand). The Motronic fuel relay is involved in both running the pump and opening the injectors. You need to verify that the side stand safety switch is making the connection to the relay so the fuel system has the potential to operate regardless of whether you are using the side stand. If the Motronic fuel relay is faulty if might affect both fuel pump operation and fuel injector operation. Below are extracts from the K100RS/K1 riders handbook and a diagram of the 4V K1/100RS starting path from the Motronic 2.1/2.2 training manual.

I apologize. To attempt to rectify my mistakes I will clarify.

We tested the injectors outside of the system, not using the engine harness. We tested that each injector opened when voltage was applied to them individually, not thinking to test them using the harness. We made a wrong assumption.

Before replacing the pump we noticed that the tank was no longer wired in 'properly' instead it was wired into a box that connected to the battery. We again, assumed wrongly that this wouldn't cause issue. We replaced the charred wires inside and outside the fuel tank. Upon applying power to the pump, our new wires started to smoke and so did the pump, it had shorted. We then replaced the pump and the wiring again.

The previous owner had caused significant damage to the wiring though both cutting and melting. As such stock wiring to the tank was gone (Cut short from the source) but we've found them though the wiring diagram (Using a suggestion made previously in this thread, to see if the pump is being initialized), which is why we now know fuel isn't being pumped during normal operation now.

I/we wrongly assumed information. 

1. We thought that as previous owner had bypassed the fuel relay and fuel was being pumped around the system it should work. I was so used to this I forgot to mention it in my original post.
   
2. Believing as the spark plugs ignited that the injectors would too, not testing to see if they worked using the harness or tested to see if there was voltage across the plug pins.
   

We have now replaced the fuel relay and that has made no difference.

firstle wrote:
plug leads on the correct plugs order ?......... sorry my fault , on the coils , i have seen this done more than once

Honestly it was my mistake. Sorry to have messed this up! We verified that plugs 1 and 4 were connected to coil #1 and that 2 and 3 were connected to coil #2. When I checked, I couldn't find a way to connect them in another configuration as the plug cables appeared short. Having another look at it, I can see how they could be connected incorrectly and I should have given more information.

I haven't checked the side stand switch, but my father says he has and it is working. The side stand is not down when we attempt to start the bike. However, as ever with this bike we will now check the wires to see if they reach their intended destination. He verified the switch worked but not the cabling, fingers crossed this will be the silver bullet.

Thanks for all the help.

On the side stand switch, on a normal 4v K, if its down the fuel pump will not prime when you turn on the ignition. A simple check is to put bike on centre stand with side stand down, turn on ignitin and then retract the side stand- you should hear the pump prime.

If you have original or our regular non original replacement plug leads they can be connected incorrectly. No 1 and 4 leads are connected to the front coil, 2/3 to the rear coil but thats assuming original standard wiring.

Your plugs should have an R in the code for resistor plugs and if you do have original BMW plug leads and caps they could be ballcocksed at this stage.

Now if you are having both firing and pump issue they should have signal from the start button......you have the correct relay? polarity on the fuel pump is correct? If you have non standard tank wiring this may have got reversed and the pump is running backwards? A quick check is disconnect the filter then run the pump, it pumps through the filter, so you should see pressure. Also, the units work by controlling the earth side so you do need to check all your earths are in order.

So. Here is an overview of the current state of affairs:

• Side stand - works and Fuel relay triggers cut when it is down.
  
• Spark plugs - Work and spark with the starter cranking the engine.
  
• No fuel pump initialization on ignition turn.
  
• No Injector trigger voltage when trying to start.
  
• Pin 3 on the ECU is positive, from what I've read it should be negative.
  

To reply @92KK 84WW Olaf - Thanks for your help.


We observe a difference in electrical behavior, the positive voltage coming from the stand is cut when it is down and comes back when it is up.

We have the originals and we've confirmed that they are in the correct order/correct coil connections observed. Being that plugs 1 and 4 were connected to coil #1 and that 2 and 3 are connected to coil #2.

Loving the term "ballcocksed" they aren't in great condition at this point and I will replace them if I can get this machine running!

Polarity is correct from what we can tell, whatever way we connect them (observing the wiring diagrams we have it would appear we have it correctly wired) as it will not run, I cannot be sure. Connecting the pump directly to the battery pressurizes the system and pumps in the correct direction when we've tried that.

We've gone over all the grounding points, cleaned them up and checked each brown cable to their termination points, making sure they have continuity! They do.


This leads me to ask a question which may be stupid, but I cannot find the answer. Why would the ECU pin 3 be positive 12V when it is meant to be ground? from what I can tell, it looks like the ECU may be fried in someway...

Thanks to everyone for helping me with this.

th2000125 wrote:Why would the ECU pin 3 be positive 12V when it is meant to be ground?

Here is the plug socket for pin #3. Is that the same as your reference?

To add to Laitch's reply: if you lever the rubber 'seal' out of the plug you will see the pin numbers molded next to the terminals. The rubber seal is loose so you won't need a new one and you shouldn't damage it.

Hi both,

I won't have access to the bike until next weekend, but my father removed seal as per your instructions @Dai thank you.

He has confirmed that it is pin 3 on the ECU, he couldn't get his camera to focus on the numbers whatever he tried. Attached is a photo. the brown and blue wire connects to the relay.