LML Star 4T auto fuel gauge problem ? By rob63 (Read 4,433 times)

[rob63]

We`ve got a LML Star 4T automatic in the workshop with a non working fuel gauge. I must admit I`m a bit stumped by this thing, the distributors technical department are about as much use as a chocolate teapot so I`m hoping someone will have a eureka moment on here.
There are 2 wires from the fuel level tank sender, one black and one black/white. The black is the dedicated earth for the bikes circuit, the black/white sends the signal regarding the level to the gauge. The main power to the gauge is a grey wire which strangely comes not from a constant positive feed, but from the regulator.
With ignition off all three wires on gauge are earthed, with ignition on all three are still earthed. Once scoot is started the grey wire provides power but this is where it gets odd.
If I connect a multimeter, red probe to grey wire and black probe to earth, I get a negative voltage reading, whereas you`d think it would be +12v. If I connect the black probe to the positive battery terminal I get a positive reading, peculiar ?
If I use a power probe and touch a positive feed to the grey wire on the gauge nothing happens, if I disconnect the grey wire and touch positive to the connector on the gauge the needle moves a gnats whisker, and that`s with a full tank of fuel.
I have replaced the gauge as I thought it could be knackered but it hasn`t made a difference.
Any thoughts please ?
Here`s the wiring diagram....

[Alleyoop]

Have you taken the float sensor out of the tank and see if moving the arm up and down moves the gauge?
It could be the Float arms plate is loose and not making contact with the resistor plate. The Float Arm Plate has tiny contact that ride on the resistor plate. If the plate is loose it will not register.
Alleyoop
Look at this thread so you can see how the float sensor works:

scooterdoc.proboards.com/thread/8701

[cyborg]

stellas (lml star to the rest of the world) have notoriously faulty sending units,,,but thats the manual bike,,i doubt it if they changed it on the auto 4t ,,,,and nothing really works well on the bike unless the engine is running,,,,almost everything runs off the mag,,,,

[rob63]

Thanks for the replies lads

Have you taken the float sensor out of the tank and see if moving the arm up and down moves the gauge

Factory time for replacing the fuel sender on these things is 4 hours Alley. They say you have to drop the motor out completely to get to the sender, however....
The part time chap came in today so we took a step back, joined heads and started from scratch. We thought we`d double check the gauge so I put a positive feed to the grey wire and just by accident the probe earth wire touched the black and white pin. Hey presto the gauge read full. Confusing as the black and white pin already had a good earth to it. We checked continuity of the wires and all was good.
We traced the wires back and found a multiplug with a black and a black/white wire deep within the rear frame. I disconnected the plug and joined a piece of wire to both terminals, started the engine and the gauge started reading full.
From this we deduced that (as Cyborg pointed out) the sender is knackered. This was an odd find as the resistance specs from the factory for the sender were spot on when checked.
We ordered a sender and I set about removing the old one.
First step was drain the tank, there is a small tube on the bottom of the tank which when disconnected from the vacuum pump drains the tank completely.
Next was remove the air intake hose between the carb and filter box. Then remove the rear shock absorber. Then remove the airbox cover and air filter, once done you remove two 8mm bolts on the front of the box, one 8mm bolt on the rear of the box along with a philips screw holding the box/mudguard to a metal bracket. (all of this is a bit of a squeeze). Pull out the airbox/mudguard.
You can now just about access the four sender screws, remove them and then jiggle the sender from the tank.
The removal process took about an hour once I`d figured it out, cutting the factory time in half and no need to remove the engine.

[Alleyoop]

Factory time for replacing the fuel sender on these things is 4 hours Alley. They say you have to drop the motor out completely to get to the sender, however....

Just like car dealers, their time to replace or do something is inflated 3 fold only so they can charge for more labor time. If it take anyone 4 hours to pull a motor out of a scooter you have to question their abilities.
You proved my point about the work involved, took you all of an hour an did not even have to drop the motor.

I try and tell everyone if you can turn a screwdriver you can work on your scoot and save yourself TONS of money. All you need is some tools and not a lot really, a good socket set to cover the size nuts on the scooter usually the largest is 18mm.
Working on the scoots is not hard and they are not complicated IF YOU CAN CHANGE A LIGHT BULB ALL BY YOURSELF you can work on your scooter.

But check it out and find the largest nut and measure the nut and get a socket set with a socket that will fit that nut. You may find an ODD ball like the one holding the CLUTCH together which is a pretty big nut, but you can just buy a good size 10" or 12"adjustable wrench to cover any odd ball size nuts.
Alleyoop

[rob63]

All very true Alley.
Sometimes I do wonder what is going through designers heads, the fuel tank on the 4t is mounted on the side of the bike behind the right side panel, the sender is on the left of the tank, inside the frame and blocked by everything but the kitchen sink. On the right side of the tank which is immediately visible once the side panel is off, is nothing but a flat surface. Why they didn`t mount the sender on there where it`s a quick and easy job baffles me.
And as Cyborg said most of the stuff works off the mag, it seems strange to have a fuel gauge which doesn`t work until the engine is running.

[cyborg]

I guess the person that designed it figured it would never fail,,,,they probably thought if it doesn't run you don't need the fuel gauge,,,,idiots,,,altho I must say they made up for it with a great kicker,,,,1-2 shots dead cold and the ol Stella lites right up!!!!,,,

[cyborg]

Oh as a side note,,,be very careful putting that damned handlebar/ gauge cover back on correctly,,,take your time and make sure everything is tucked back nicely or pinched wires are in your future,,,a bigger piece of sh!t has never been designed,,,,ask me how I know

[jct842]

Try working on a yamaha majesty, the jap who designed that pos was just out of grade school and had a big brother that owned a plastic factory. (Note to self...get that damn thing on craigs list..soon)

They are all great until you need to work on them...then we sort out the garbage

[rob63]

Nov 11, 2015 21:10:14 GMT -6 cyborg said:

Oh as a side note,,,be very careful putting that damned handlebar/ gauge cover back on correctly,,,take your time and make sure everything is tucked back nicely or pinched wires are in your future,,,a bigger piece of sh!t has never been designed,,,,ask me how I know

I hear ya buddy. The last Vespa I had was a batteryless PX, simplicity itself. When I took off the headset on the 4T, I wondered how I was going to get all the multiplug connectors back into that space.... very carefully was the answer

[rob63]

Sender is in, all working well

[cyborg]

GOOD ON YA LADDIE!!!!!!!!!!!!!!!!!!!!!! Glad you got it up and running,,,man those nagging nittley problems drive me nuts

[russzil]

Hi 
i also have developed a fuel gauge issue on a 2014 LML 4t automatic, when started the gauge will show about a quarter full (the tank is absolutely full) when the rear brake is applied the gauge shows empty, releasing the rear brake and revving the engine make the needle rise a little bit, applying rear brake sends it straight back to empty, any ideas, suggestions?

[cyborg]

YOU HAVE A SHORT IN THE WIRING IN THE HEAD SET UNDERNEATH THE HANDLEBAR COVER,,,ITS A MAIN PAIN IN THE DRAIN TO GET EVERYTHING BACK IN THERE WITHOUT PINCHING WIRES,,,ONE OR TWO MUST HAVE RUBBED TOGETHER,,,TAKE OFF THE HANDLEBAR COVER AND MOVE WIRES AROUND A BIT AND YOU'LL PROBABLY FND THE PROBLEM GOES AWAY,,,THE TRICK IS TO GET THAT COVER BACK ON WITHOUT RECREATING THE PROBLEM,,,I THINK A FEW PEICES OF ELECTRICAL TAPE IN THE RIGHT PLACES WILL MAKE THE PROBLEM GO AWAY PERMANENTLY