Fuel Gauge Mystery Follow up

I finally resolved my Fuel Gauge dilemma. Here is a photo of the variable resistor of the sending unit on the fuel pump. You may notice a slight orange/brown haze on the element. This, I presume, is sulfur deposits from (less than premium) fuel. Those deposits were increasing the resistance of the sending unit and causing the fuel gauge to become erratic.



I also noticed that there was about 1-2 MM play (in & out) of the wiper section of the sending unit. This seemed to be caused by the push-on lock washer which anchored the float arm to the sending unit not having been pushed on tight enough. So the poor contact of the wiper exacerbated (Ooo, I always wanted to use that word) the resistance caused by the deposits.

After disassembling the sending unit I used an old toothbrush and a q-tip to scrub the resistor surface with contact cleaner as well as some Techron.

With the fuel tank reinstalled in the scoot and after several test tanksfull I can state that the problem has been resolved.

So now I'll have to stick with using premium-branded fuel rather than the "bargain" fuel I had been using.

Ya gets what ya pays for

Tim

I was lead to believe the sulfur problem was in the process of combustion not a fuel tank condition, does the tank have this coating also?

Great post. Taking the time for a follow up like this is part of what makes this forum so great. Howard

oldgwingguy wrote:

I was lead to believe the sulfur problem was in the process of combustion not a fuel tank condition, does the tank have this coating also?

I am not 100% sure that it is sulfur, but it sure is a sulfur colored deposit.

There is no discoloring in the tank.

Sorry that photo is so small. It's the first time I actually figured out how to post a photo, and it's the largest view I could do on this attempt.

Tim

Roger that, a good call on fixing it yourself good explanation on the fix.

Nice one Cosmic!
Sounds like it was as suspected then.
I wouldn't worry about what fuel you use. Now that you have taken out any slop in the mechanism the wiping action of the blade will keep the rheostat clean and stop any deposits from forming.
Thanks for the update.

Great post Cosmic. When ever I fill the tank I add one or two ounces of Lucas injector cleaner and fuel stabilizer ( Techron or Marvel Mystery) which should keep the fuel sending unit and injectors clean even with low grade fuel...I think

I had been adding a bit of Techron to each tankful for quite a while, but bumped up the amount when the fuel gauge began acting up.

Sadly, a month after finally removing the tank and fixing the sending unit, the scoot was totaled when I hit an oil spill and heard the heartbreaking sound of crunching plastic.

But after 13 years and 97000 miles it gave me a good ride.

Tim

Sorry about your accident. Around here it's getting toward that time when one has to be careful on the roads. We have a pretty hot summer in these parts with little rain. Pretty soon the rain will return and the roads will be treacherous with rain bringing up the oil on the road that cars have left on the pavement. Especially in the center of the lanes.

There shouldn't be any sulfur, or very little in US gas that's one of the things the new fuels have practically eliminated in gasoline and diesel.

http://transportpolicy.net/index.php?title=US:_Fuels:_Diesel_and_Gasoline

Thanks, I nave a fuel sending unit problem. I’ll try your technigue.

Cosmic_Jumper wrote:

I finally resolved my Fuel Gauge dilemma. Here is a photo of the variable resistor of the sending unit on the fuel pump. You may notice a slight orange/brown haze on the element. This, I presume, is sulfur deposits from (less than premium) fuel. Those deposits were increasing the resistance of the sending unit and causing the fuel gauge to become erratic.



I also noticed that there was about 1-2 MM play (in & out) of the wiper section of the sending unit. This seemed to be caused by the push-on lock washer which anchored the float arm to the sending unit not having been pushed on tight enough. So the poor contact of the wiper exacerbated (Ooo, I always wanted to use that word) the resistance caused by the deposits.

After disassembling the sending unit I used an old toothbrush and a q-tip to scrub the resistor surface with contact cleaner as well as some Techron.

With the fuel tank reinstalled in the scoot and after several test tanksfull I can state that the problem has been resolved.

So now I'll have to stick with using premium-branded fuel rather than the "bargain" fuel I had been using.

Ya gets what ya pays for

Tim