Alternator Belt needs replacing - Or Does it ?

[Magwych]

Hi,
Think I know the answer to this already but once again I appeal to the common collective for its opinions ...

When I start off from work for my journey home with a small amount of fuel and the display showing miles to empty, the number of miles plummets quite dramatically, yesterday by 10 miles in 400 yards.

When I start form home under the same conditions, the display is far more accurate.

Work is in the City, and home is quite close to the motorway to get me there.

The bike is an early '06 1200GS, with 33,000 miles, servo brakes, heated grips and HIDs.

My first thought is that the alternator belt is probably losing a lot of tension by this number of miles, and is slipping thus preventing the alternator from supplying sufficient current to cope with lights and the electric servo. Checked this theory yesterday by turning the lights off. Within about 2 minutes I had gone from only having 30 miles left to empty to having so much fuel that the guage could no longer be bothered to tell me how many miles were left til empty. Turned the lights back on, and after a short time, sure enough, the fuel guage fell, yellow warning triangle, 39 miles to empty ...Once I got out of town and onto the motorway the guage climbed back up again and I did another 30 miles before it came on again.

So, my question is whether you think or aware of anything else I need to check? We are off with Moto-Morrocco in November for the Novice trip , so need to get this sorted before we go, clearly the battery is not coping with the bikes requirements when running at city speeds, and I do not envisage tearing around Morocco at motorway+ speeds

 

[cookie]

i don't think the alternator belt has anything to do with it.

 

[The White Rabbit]

i don't think the alternator belt has anything to do with it.

When my belt went it was characterised by a 'whosshing' noise, everything was fine until it snapped and the charge light came on, and then everything died in a nice sequence. So I would agree, at least it wasnt my experience of a worn belt. As an aside at those miles I think the belt is ready for a change and it may be mine wasnt slipping as such, just damaged.

 

[Magwych]

i don't think the alternator belt has anything to do with it.

Any clues what you think it might be ?

 

[cookie]

Any clues what you think it might be ?

i was deliberately vague to avoid saying that i didn't know what it actually was

probably the notoriously inaccurate fuel gauge in league with the calculating nature of the trip computer

 

[Magwych]

Damn, I was hoping you some great insight there ..

It seems the problem only materialises when I am driving in town, lots of idling and use of brakes; out of town it disappears. I should have also mentioned that the R|ID backlight seems a bit dimmer when this is happening too. Hence I am assuming it is a voltage drop that is occurring in the higher drain conditions, my first guessses are battery or charging circuit. The battery does not seem to suffer from being left for a week or two without use, so I leaning towards charging circuit. If it was adjustable, I would tighten the belt to see what happens...

 

[cookie]

Damn, I was hoping you some great insight there ..

It seems the problem only materialises when I am driving in town, lots of idling and use of brakes; out of town it disappears. I should have also mentioned that the R|ID backlight seems a bit dimmer when this is happening too. Hence I am assuming it is a voltage drop that is occurring in the higher drain conditions, my first guessses are battery or charging circuit. The battery does not seem to suffer from being left for a week or two without use, so I leaning towards charging circuit. If it was adjustable, I would tighten the belt to see what happens...

it's probably your city riding affecting the trip computer's calculation. it is constantly recalculating, so stop start traffic straight off will be what it bases it's figures on, if that's what it first sees. it will even out later.

 

[Deleted account 210609001]

Easy way to check if it's charging would be to buy a multimeter and check the voltage across the battery terminals - 10 second job to take the seat of and there you go. You could easily do this when it's cold, hot, home, work, whatever.

Here's my bet: at home, you put the bike on the centre stand, at work it's on the side stand. Side stand affects the apparent fuel level, and the change when you leave work is because the bike is upright again. As far as the fuel gauge is concerned, the level has dropped by a couple of litres.

When I fill my bike up, it can take a hundred yards or so for the fuel gauge to register full, even when th etank is brimming...

I don't know exactly how the fuel gauge sender works, but I doubt it's going to be voltage sensitive. My fuel gauge does some funny things at or around the point where it starts to show miles remaining.

Finally, my RID gets pale (i.e. the black isn't quite as black) when it gets hot. Being stuck in traffic, especially in the sun, makes this worse. In Italy this summer, crossing Milan, it all btu disappeared. It shouldn't happen, I know, but I don't think that was anything to do with reduced charging either.

 

[littleredrooster]

I concur; it almost certainly is not the battery voltage. Mine does something similar when the 'remaining miles' cuts in; there is a certain sequence of acceleration and braking which will shift the fuel to the side of the tank where the sender resides. This will extinguish the fuel light for a few miles altogether sometimes before it comes on again. I would wager that the riding conditions are different when you leave home compared to when you leave work - this can give the different display results.

My experience also suggests that it errs on the side of caution; I've had the display down to 2 miles remaining and still not managed to get any more than 18 litres into the tank.

 

[GSmonkey]

I'd think you've got two things going on. City riding certainly does mess with the sensor. I would often get a low fuel light, which would then reset when stood at lights for a while. The computer will average the signal out so as not to continue to give spurious amounts hence the delay normally seen to register a full tank or clear the low fuel light.

With miles-to-go indicators on cars and bikes, you always 'loose' miles when stopping the bike then re-starting from cold. I assume these indicators take a signal from the fuel management system and predict the range. When doing a cold start you're using much more fuel hence the range plummets. If you get the bike up to temp then start cruising again, you'll normally re-gain some of the 'lost' miles.

 

[Fanum]

it's probably your city riding affecting the trip computer's calculation. it is constantly recalculating, so stop start traffic straight off will be what it bases it's figures on, if that's what it first sees. it will even out later.

This makes a lot of sense- the figures are predicted figures based on use, so if you jump on te motorway close to your house, the figure will drop as you hit motorway speeds.....on the way home through town though, initially at least you'll be potling a lot more which will make the ECU recalculate accordingly


PS I'm just guessing but I've had similar things happen on a Saab with one of those ecometer thingies

 

[red rocket]

I was going to ask a similar question.

3 month old 3000 miles picked it up Friday.It has the computor fitted not sure what the standard fuel warning says compared to mine but I can see at any time the tank range .
I went out for a ride with some vfr's etc yesterday with a range of over quite a bit over 100 miles.
We did a relatively fast stretch through the twisties then after no more than about 30 miles if that we got to walking pace in Dereham town traffic.

I glance down the fuel warning light is on and it went down from asomething like 60 to under 30 mile range in about half a mile of slow moving traffic.

I was convinced it must be pissing out all over my feet but alass no.

We get out of the town & it starts to slowly rise again to around 70 miles & no more warning light.

So whats that all about then

 

[Deleted account 210609001]

Regardless of the computer stuck on the end, fuel gauges are never that accurate as fuel sploshes around the tank. Technical term there.

Zero the trip meter when you fill up. Allow 10 miles per litre. That'll give you a bit of leeway. Bob's your uncle.