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Fuel Gauge Drops to Empty - Gas Tank Still Full. Thoughts? Ideas?


Olive

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About a month ago riding home from work I glanced at the gas guage. One bar shy of full. The next time I glanced it had dropped two more bars. Odd. It continued to plummet, and I nervously checked my mirrors to see if there was a liquid trail following my bike. All was normal. Down to one bar then blinking red. That made me nervous enough that I pulled into the first available gas station and filled up the tank - a whole $1.12 worth of gas brought me right back up to the top.

Pulling away from the gas station the guage continued at flashing red, slowly rising back to display full. (Slow response of the gas gauge after filling is quite normal for this bike - seems to take a few blocks before the gas level displays correctly).

This weekend I had a repeat performance of flashing red on a tank that was 3/4 full. I opened the tank and checked - lots of gas. Opening and closing the tank didn't change anything. The guage continued to register as empty until the next time I filled the tank - 250 km later. After filling the tank the gas gauge once again returned to normal.

I have had this happen a few times now - definitely not my imagination. (Gerry02800 can vouch for that!). It doesn't seem to be connected to temperature or humidity. Each time the issue is resolved when I refill the tank - either from the partly empty state or the full empty state.

Any ideas? Thoughts? Suggestions?

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The FSM says to check the resistance of the wiring with the float at the top and bottom - 1 to 5 ohms full and 92 to 96 ohms empty. If out of spec look for an open or short circuit. But that doesn't sound like the symptoms you're describing. Could it be that the float mechanism has gotten gummed up a bit from some deteriorated fuel? If so, maybe some fuel system cleaner (SeaFoam, etc) could help. Alternatively, maybe one of the floats has developed a leak - like happens to carburetor floats. Seems like an odd problem. I have never been happy with the fuel gauge - it seem like the 1st bar drops off within about 10 minutes after filling up.

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I think Cogswell is on the right track, probably the "float" inside the tank, this was actually the case on my Ducati. The level gauge was actually staying in the "low" state condition even after filling it up for many fill ups and sometimes would eventually go off. Another time the level gauge never went down and I completely ran out of gas because the fuel light never came on, on the 95 Duc your only indicator of where you are fuel wise, is the odometer and the fuel light. Funny story here, I had just pulled off the freeway and the bike shut off at the end of the off ramp, it wouldn't start so I pushed it across the street where some gardeners were trimming the lawn of a hotel. I opened the gas tank and it was empty! Luckily I was able to bum a gallon of gas off the gardeners, which was enough to get me down the road to where the gas station was.The gauge was eventually replaced and all has been good ever since. Knock on wood!

Keep us posted as to what you find.

Cheers

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I would venture to guess it has to be electrical. The float typically works (floats) or it doesn't, so the slow to react thing makes me think there is an issue with reading the resistance or sending that resistance to the gauge. Since you have another bike, you could always just swap the tanks and see what the other tank does. That would verify it's either an issue with the tank (fuel level sender), or with the gauge.

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The FSM says to check the resistance of the wiring with the float at the top and bottom - 1 to 5 ohms full and 92 to 96 ohms empty. If out of spec look for an open or short circuit. But that doesn't sound like the symptoms you're describing. Could it be that the float mechanism has gotten gummed up a bit from some deteriorated fuel? If so, maybe some fuel system cleaner (SeaFoam, etc) could help. Alternatively, maybe one of the floats has developed a leak - like happens to carburetor floats. Seems like an odd problem. I have never been happy with the fuel gauge - it seem like the 1st bar drops off within about 10 minutes after filling up.

Appreciate the responses guys - keep them coming!

Cogswell/Duc2V4:

The gummed up idea certainly would explain why it is so slow to react to changes in fuel level (i.e. filling up the tank), but doesn't seem to explain the occasional situation where the fuel gauge plummets like a rock. A float leak wouldn't be consistant wtih the behaviour of the gauge responding normally after adding $1.12 worth of gas to top off the tank.

On measuring the resistance of the wiring - could you give me a detailed walk through of exactly where I would check this? Which wires? Photos could be useful as well. (Imagine me standing in front of the bike holding a multimeter with a puzzled look on my face - how do I do this?)

Hondalover:

Very true, I do have the second bike which gives me an opportunity to start swapping bits and pieces. However, I would rather check out the potentially easier solutions before going through the pain of swapping tanks.

Definitely an odd problem - and one that is inconsistant. Those are the hardest to troubleshoot. I am accustomed to watching the odometer to guage when I next need fuel (previous bikes didn't have the luxury of a fuel guage), but flashing red "almost out of fuel" still has me searching for the nearest gas station just in case the bike knows something that I do not.

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No photos on hand, but the FSM on page 20-19 shows removal of the fuel level sensor connector and sensor itself from the bottom of the tank (just 4 bolts). You'll need to be able to move the floats back and forth manually to check them. If you don't mind draining the tank and removing it, it shouldn't be too bad of a job. Once out, the sensor can be re-connected to the wiring harness to see if the LCD responds correctly the to floats - there's a process shown for that as well.

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No photos on hand, but the FSM on page 20-19 shows removal of the fuel level sensor connector and sensor itself from the bottom of the tank (just 4 bolts). You'll need to be able to move the floats back and forth manually to check them. If you don't mind draining the tank and removing it, it shouldn't be too bad of a job. Once out, the sensor can be re-connected to the wiring harness to see if the LCD responds correctly the to floats - there's a process shown for that as well.

So not something that can be tested with tank on bike. The problem is that I do not have a garage. Nice weather I want to be riding, not wrenching. Not so nice weather - not conducive to wrenching.

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High resistance = low fuel gauge reading. An open circuit reads totally empty.

So, it's either a bad connection at the fuel level sender or a float issue. My money is on electrical gremlins, so raise the tank and check the plugs and pins for any signs of corrosion. Also look for damaged or pinched wires.

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High resistance = low fuel gauge reading. An open circuit reads totally empty.

So, it's either a bad connection at the fuel level sender or a float issue. My money is on electrical gremlins, so raise the tank and check the plugs and pins for any signs of corrosion. Also look for damaged or pinched wires.

Couldn't agree more.

The float contact arrangement was actually quite primitive on earlier bikes, I haven't been into one since my 3rd gen and the intermittent open circuit could just simply be the contact which the float slides up and down the resistor, a GENTLE bend can make this work better, perhaps there may even be some boogies on the contact patch from some crook fuel? Of course the sender needs to be out of the tank to check all of this.

The red warning light is simply a function taken from the same fuel level reading going to the gauge.

The readings can be calibrated in a rough fashion at either end of the scale i.e. full or empty by bending the support mechanism the appropriate direction. It's a long drawn out process but for those who are anal (guess who?) about their instruments telling them the 'truth' it is worthwhile. One just needs to determine whether the float needs to be higher or lower at empty or full for wherever your reading needs to get to! Work it out on paper if you have to using Kaldek's simplified equation above.

Because of the shape of VFR tanks it is almost impossible to have this linear across the full range but it's a great way to get rid of the annoying first bar disappears when leaving servo or last bar telling you are still 1/4 to 1/2 full.

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here's what I would be tempted to do.....find the wires that connect the tank mechanism to the wiring harness. disconnect. if the bike runs correctly & doesn't display error/check engine codes & if the odo function is working right use that as a "guage", I'm pretty sure you know roughly how far you'll get on a tank(L/km used, consumption average,etc.) work on it after this last part of the riding season, borrow a friends garage or whatever to get shelter from the wx.

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Hmmm... Gremlins again this morning.

A little chilly 9C (48F). Turn on bike. Glance down. Flashing red last bar of fuel guage. Hmmm... Just put in $19 worth of fuel last night, so it should be full. A quick slosh verified the fact.

Started riding in to work. Blinking red turned to one bar. One bar turned to two. Gradually the tank "filled" and about 5 minutes later I was reporting a full tank again.

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After several years of a pampered life in Jokers garage, the bike is just not happy with all of your riding and parking in your driveway. Rode hard and put away wet comes to mind. Sorry, I just had throw in my two cents. Hope you find it before your season ends. Mine is about to start.

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My guage starts blinking red after 200 miles and I still have 2 gallons left. Been happening ever since I got the bike over a year ago. Been meaning to dig around but always get distracted fiddling with other stuff in there.

Hopefully you get your issue resolved soon, Olive. I'll be lifting my tank this weekend.

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After several years of a pampered life in Jokers garage, the bike is just not happy with all of your riding and parking in your driveway. Rode hard and put away wet comes to mind. Sorry, I just had throw in my two cents. Hope you find it before your season ends. Mine is about to start.

Well, as soon as I got the bike re-education began. I rode through rain. I rode on slab. I found high winds. Coated it in mud going through a really rough construction zone (I had mud on my helmet just to put things into perspective). Then a blizzard followed by a few days of snow.

That was all in the first week before I even left the States. Not sure if the bike or Joker had the hardest time with that. :tongue:

As for the driveway, the bike doesn't spend much time there. I lavish it with attention, take it everywhere and even bring it to work each day. This bike is really pampered - they are built to be ridden ya know! (Just don't tell it about our six month parking season... The bike might try to make a break for it and head back to Atlanta. :ph34r: )

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  • 8 months later...
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Just thought that I would update this thread. I didn't have the opportunity to dig into the issue further last year - I spent the time riding rather than wrenching. Plus, since the issue was intermittant trying to troubleshoot it could be very aggrivating.

Winter came early and I was fortunate enough to find indoor storage for the bikes... that was last October. Picked up the bike and noticed that it was reading "totally empty" - flashing red despite having a full tank. Have had the opportunity to commute a few times (including the requisite detours on the return trip), and have topped up the tank, but the bike still wants to be a flasher. Poor bike continues to insist that it is very thirsty and needs a refill, despite all evidence to the contrary.

Looks like I will have to roll up my sleeves and do some investigation.

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Either your fuel sender plug (blue plug underneath tank) has become disconnected or corroded, or the float inside the tank has failed somehow. It's also worth checking the continuity between the gray/blue wire all the way from the plug under the tank to the sub harness on the front-left of the bike.

The way the fuel sender works is it takes a +12 volt signal as input and based on the fuel level the resistance in the sender changes. The signal from the fuel tank is therefore either really close to 12 volts (full), zero volts (empty) or somewhere in between.

I have spares if you find a physical faulty and need cheap parts.

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  • 1 year later...

Can you please tell me if you finally found something ? Cause i've got this exact issue on my VFR and cannot figure it out. I've remove the tank, investigate further and see nothing wrong. The sender even worked out of the tank, but not in the tank. Thanks for your time.

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