Faulty Fuel Guage/Indicator

[Bright Rider]

My 2015 ST1300 PA with approximately 41000 miles cut off while riding down the road recently. The fuel indicator showed three bars worth of fuel remaining in the tank and the gauge never blinked. I was able to fill it up with 6.8 gallons of gas. Once refilled with gas the motorcycle immediately started up like there had never been a problem. I have not got back down to three bars on fuel gauge yet, but he bike runs great at any load or rpm since filling the tank. Any suggestions on troubleshooting would be greatly appreciated. Thanks -BR

 

[Obo]

My first thought is to run it down again and see if the issue repeats.
You should be able to use the mileage and looking into the upper tank to get an idea how the fuel is so you don't run out - but you can carry a small jerry can along just in case.
From what I recall, the upper part of the tank uses a float system, and the bottom uses a thermistor. (for when it gets to the flashing bars on the dash)

 

[Andrew Shadow]

Any suggestions on troubleshooting would be greatly appreciated.

See the attached for fuel gauge trouble shooting guide.

 

[Bright Rider]

My first thought is to run it down again and see if the issue repeats.
You should be able to use the mileage and looking into the upper tank to get an idea how the fuel is so you don't run out - but you can carry a small jerry can along just in case.
From what I recall, the upper part of the tank uses a float system, and the bottom uses a thermistor. (for when it gets to the flashing bars on the dash)

Thanks for the guidance. I will plan on testing the bike's range and fuel gauge again. The Lord was looking out for me last time and let me coast to the pump. Didn't have to push a step. I will plan to carry a little extra fuel with me when I test it out. Sounds like the fuel gauge is supposed to tell you just when the upper tank is getting empty and you know the bottom tank is getting empty when the thermister in the bottom tank starts causing the gauge to blink.

 

[Bright Rider]

Thanks Andrew for the fuel gauge trouble shooting guide. Just wondering did this information come from the Honda Service Manual or some other service guide? I need to get some sort of service manual.

 

[etalors]

If you filled up with 6.8 gallons. That means your tank was empty. It gets filled up a little sooner on the side stand. Meaning takes less gas to fill it up on the side stand. I have been able to add about 1/2 a gallon more on the CS. Test it again. It was probably some circuit related glitch. Probably wont happen again.

 

[Andrew Shadow]

Thanks Andrew for the fuel gauge trouble shooting guide. Just wondering did this information come from the Honda Service Manual or some other service guide? I need to get some sort of service manual.

2003 Honda service manual.

 

[TerryS]

At a first guess, you may have two issues that account for the gauge misbehaviour. The low fuel thermistor did not trigger a low level warning, so that is the most critical, it is fed battery voltage down the brown/black wire from the dash, through the thermistor, then to the earth shared by the fuel pump. Is the brown wire properly attached and the terminal clean on the fuel pump flange under the seat?

The second lesser issue is the fuel sender unit showing 3 bars when the system was empty. Could be as simple as the float and wiper arm are sticky and not moving freely, or the float arm could be bent so that 3 bars is as low as it goes.

I found a service manual online, you can access it here through Dropbox: https://www.dropbox.com/s/8ozxqkvlri7yk7s/ST1300 2003.pdf?dl=0

 

[Bright Rider]

Thanks so much for all the advice and the link to the service manual. I rode some last night to start to get the tank down to the previous level to see if the problem happens again like it did last time. This time I am going to be carry some extra gas with me. I'll get you all an update here when I get to that point. -BR

 

[Igofar]

You may have also missed seeing it blink just before turning your bike off on a ride, then it will NOT reset its self sometimes, and just run you out of gas.
Several other good suggestions here.
Let us know what happens.

 

[Mike]

I thought my 21-year-old ST had experienced every malady the line has experienced. Newest malady, the fuel gauge would go to 2 bars and stop. Checked the thermistor and it was good. I putzed about and checked the resistance between the thermistor and the pump side terminal (the epoxied one), 000.1 ohm reading. then I checked thermistor to 3 prog plug, 182.4 ohms. to isolate the issue I checked the 3 prongs plug to the connector that enters into the tank, (exposed epoxy) 000.3 ohms. resistance appears to be through the epoxied pump housing plate. I consulted the wiring manual.
Has anyone ever checked this? Is there supposed to be additional resistance through the epoxide wire?

 

[Mike]

I am convinced that the resistance is in that epoxy. I ground out the epoxy and found a ring connector held by a brass rivet. Flipped over the pump and ground away the epoxy to the rivet. Over 21 years the stake had become loose. Cleaned the connections with acetone, staked the rivet tight and the resistance was.003 ohm. Thermistor ohm remained 1,000 throughout the wire to the 3 prong connector. Pretty sure this is the fix but won't know until I get a new tank gasket. Checked in with Honda and a fuel pump is now $633!

 

[Andrew Shadow]

I am convinced that the resistance is in that epoxy. I ground out the epoxy and found a ring connector held by a brass rivet. Flipped over the pump and ground away the epoxy to the rivet. Over 21 years the stake had become loose. Cleaned the connections with acetone, staked the rivet tight and the resistance was.003 ohm. Thermistor ohm remained 1,000 throughout the wire to the 3 prong connector. Pretty sure this is the fix but won't know until I get a new tank gasket. Checked in with Honda and a fuel pump is now $633!

Someone else had a similar problem a while back where their fuel pump would not work. They traced the problem to poor conductivity between the connector on the outside of the fuel pump flange and the terminal on the inside of that flange. I think that they soldered it to get a better connection and it worked but I can't really remember, so you might be on the right path. Let us know.

 

[Mike]

Someone else had a similar problem a while back where their fuel pump would not work. They traced the problem to poor conductivity between the connector on the outside of the fuel pump flange and the terminal on the inside of that flange. I think that they soldered it to get a better connection and it worked but I can't really remember, so you might be on the right path. Let us know.

Will do.

 

[Mike]

Those are brass rivets with the eyelets of the connectors staked tightly. Over time the stake loses, why? Heat cycles I imagine. I couldn't detect the loose eylet until I ground out the epoxy. My only clue before that was the high ohm resistance. I was able to remove the epoxy on both sides of the flange and use a tool to stake the rivet tight, checked the ohm reading and once satisfied I filled the area With fuel resistant epoxy. Waiting on a new flange gasket then I'll get back and post wether or not that was the fix.