Alternator light and rev counter problem

[Marlou]

Hi all,
A little advice please, I have an 1150 adventure 2003 and when riding if I push to 5000rpm or above the alternator/charging light comes on dimly and the rev counter becomes erratic (flicks to full revs back to 5000rpm and so on). No change to the actual engine revs and the bike still rides fine however I don't like it........ Anybody come across this before. I spoke to my local BMW dealer and they said they have never come across it before!!

Many thanks in advance:

 

[NeilDD]

Couple of things to check

1/ Blue wire on back of alternator (often corrodes)
2/ Earth wires connection in loom that runs on RHS of beak back to main loom on bike
3/ Wiring from HES back to main loom

That should keep you going for a few days

HTH

 

[Marlou]

Thanks for that will have a look 1 & 2 are straight forward but what is the HES??

That's this weekend sorted out then..........

 

[NeilDD]

HES
Hall Effect Sensors or in laymans terms ignition triggers, theres one for each pot, behind the black plastic cover on the front of the engine.
Wiring can get brittle with age & heat, see Fanum's thread about his bike, which has had nearly everything including the kitchen sink changed

HTH

 

[Ian J Hartley]

Strange. Have you checked fuse 1 is ok and is making good contact with the terminals in the fuse holder. Your bike will run without fuse 1, but you wouldn't get tachometer or ignition light.

The rev thing is confusing, unless it equates to a specific vibration or resonance.

 

[Marlou]

I have not checked anything yet, I've only had the bike a couple of weeks so it's all a it new

I will have a look at fuse 1
I have not noticed any strange vibration but again it's still new (thin k I would probably notice it though. The actual engine revs do not change just the tachometer goes erratic the bike rides as normal.....

Taking it to Devon on Friday and back saturday so hope to have. Look on Sunday

Thanks for your help

 

[Ian J Hartley]

If you can before you go replace the fuse.

Your problem is indication only. I suspect you have a voltage drop on the tachometer side of fuse 1. The tachometer gets it's signal from the motronic, but it needs 12v and earth to function. If the voltage drops on this line then your tachometer will not have full voltage to operate correctly.

Also the alternator light is extinguished by having 12v from the alternator on one side of the light and the 12v from the battery via fuse 1 on the other side. As both are equal the light will extinguish. If you have a lower voltage after fuse 1 then the light will illuminate dimly.

The RPM could cause vibration to a poor connection which could generate an increase resistance causing a voltage drop. More likely is the increase in current in the wiring by higher RPM. The tacho draws more current to deflect the needle. This increase in current across a resistance will cause a voltage drop.

There could be other things wrong. But the only thing I find common to the symptoms is the power from fuse 1. I could be going too deep here, but that's the theory based on your symptoms.

 

[Ian J Hartley]

If you still can't clear the fault, then you might want to consider disconnecting the tachometer. The signal that drives the tachometer is also the same signal that the motronic uses to send pulses to the ignition coil. I would hazard a guess from the wiring diagram that these are negative going pulses, probably a square wave at the frequence determined by the hall sensors. This negative going square wave is probably amplified inside the tachometer which then drives the needle. If your tachometer has developed an internal fault then the signal could be amplified and fed onto the positive line and might be enough to give you a voltage drop to partially illuminate your alternator light. At 5000 rpm, given the coil pack fires every revolution this would give you a frequency of about 83 pulses a second.

Disconnect the tachometer and ride the bike to and above the point at which the fault appears. If the alternator light dims then the fault is else where. If you get no dimming then likely you tachometer is at fault.

Check the wiring at the tachometer connector for corrosion.

 

[Ian J Hartley]

The tachometer connector is under the fuel tank. Located on the right hand side of the headstock just below the 16mm hex head bolt of the cross member Three wire black connector with a green brown and black wire on the tachometer side and green/black, brown and black wire on the bike side.

 

[Marlou]

Hi Ian

Thanks very much I will have a look at that on Sunday and report back,

 

[Ian J Hartley]

You might be able to disconnect the tachometer plug without lifting the tank. If you look between the headstock and the tank you should see the connector. If you have small hands you might get to it. Saves a lot of hassle if you can.

 

[Marlou]

Hi Ian,
It's had headlight conversions so the ballast units are sat eitherside of the tank right in the way (that's mr sod and his law for you) having said that my shovels would not fit anyhow.

Don't think this will change anything but the bike does not have to be moving, if on the stand and I rev it it does the same thing at 5000rpm ish.

Will have a look and take it from there.

 

[Marlou]

The weather gave me the opportunity to have a look today and behind the clocks the previous owner has cut the tachometer feed cable and joined it with butt splice connectors.
Bodger I think, anyway I think I will either replace the counter and plug in as normal or get some better waterproof connectors.

Now the revs are fine no fluctuating at all but the charge light still comes on dimly at about 4500/5000 rpm then quite bright by about 8000rpm when on the stand.....

Could that be a belt/alternator problem??

 

[B4ndit]

8000 revs? When standing.

 

[Marlou]

8000 revs? When standing.

Yea just built up and gave it a hand full

Didn't perticularly like it (in fact it stalled after) but just wanted to see how bright it got! My blade has no problem with that didn't think BMW would either?.

 

[DrFarkoff]

go and buy a multimeter and test the volts across the battery red to red and black to black! If you are getting 13.5 volts and over at tickover and above you have a good charge circuit

If not you need to do more tests

Don;t Rev it at a standstill It's really not good for it!

Yea just built up and gave it a hand full

Didn't perticularly like it (in fact it stalled after) but just wanted to see how bright it got! My blade has no problem with that didn't think BMW would either?.

 

[Marlou]

go and buy a multimeter and test the volts across the battery red to red and black to black! If you are getting 13.5 volts and over at tickover and above you have a good charge circuit

If not you need to do more tests

Don;t Rev it at a standstill It's really not good for it!

Life is about just trying things is it not? I understand the
Fundamentals of electrics ac & dc so red to red black to black! Is not a nesseccary statement

There is no issue with charging I think that an earth fault is most likely but thanks for the reply

 

[Ian J Hartley]

Good to see you've sorted your tacho, at least you now know you have two seperate faults.
Checking your charging circuit out with a voltmeter is good way to go. It would be a good piece of mind as you suggest to check you belt for condition and tension at least you will have eliminated a possible problem. Also check the electrical connections on the alternator for corrosion as has been previously suggested in this thread. Assuming your battery is good and everything else looks Ok (connections good and tight). High rpm faults might be the voltage regulator or worn brushes. You will see this by monitoring the voltage from the alternator it will probably remain relatively stable until you hit the rpm and then drop off sharply the higher the revs.

 

[Marlou]

Have taken it out for a ride to see if under load all is ok and everything is the same as before (knackered) must be the vibration as you say. I think that I will replace the tachometer splice connectors (solder and heat shrink) and see what I find from there as maybe it will cure both.

I did double check the voltage at the battery When at idle as Drfarkoff suggested and it is good (13.8)

It has a full tank of fuel at the moment so don't want to remove it till I have to.

Thanks for your all help so far it's much appreciated

 

[DrFarkoff]

Life is about just trying things is it not? I understand the
Fundamentals of electrics ac & dc so red to red black to black! Is not a nesseccary statement

There is no issue with charging I think that an earth fault is most likely but thanks for the reply

Not meaning to cheeky but How do you know there is no issue with charging?

The brushes may be worn and jumping at speed if you run the bike with the heated grips the hazards and main beam you may see the lamp glow brighter at lower revs and check the volts at tickover then monitor volts against revs against glowing lamp you will be sure of a alternator fault or earth fault

Have fun

EDIT Also check the wiring from the headstock to the instruments the solid brown wire is the ground for everything on bmws and on more than one occasion I've come across splits or damaged wires due to corrosion leading to false earths and using warning lamps for grounds