Fuel level sensor behavior?

[Joe Frickin' Friday]

'99 RT, 115K miles. Last summer my fuel gauge started misbehaving:

 

-the RID does not show all bars when full, or if I really top it off to very full, the top bar disappears soon after leaving the gas station.

 

-When nearing empty, the last bar disppears off of the RID long before it used to.

 

The idiot light still behaves as it always has, coming on with about a gallon left.

 

So this afternoon I pulled the level sensor from the tank, expecting to see the side dented in as others have (a symptom of excess tank vacuum/pressure secondary to a clogged vapor recovery cannister). I was shocked and confused to find it in perfect condition, no dents apparent.

 

I measured the resistance at the connector with the float slid all the way up and all the way down the barrel; I measured 4.5 ohms and 77.5 ohms, respectively. The manual doesn't give specs; can someone confirm whether this is correct?

 

The sensor appears to be permanently assembled, so I can't inspect the float without destroying the whole thing. My suspicion is that it's an air-filled float that has developed a leak, and is therefore floating lower (with respect to the actual fuel level) than a healthy float would. Does anyone know what the float is made of?

 

Any suggestions, short of outright replacement?

[Boffin]

Check and clean the connector to the RID. High resistance here from muck or corrosion will cause this symptom.

 

Andy

[Joe Frickin' Friday]

Check and clean the connector to the RID.

 

Just to confirm, you're talking about the connector behind the dashboard (behind the actual display module), correct? If so, can do; the challenge now is to reassemble my fuel tank.

[Boffin]

That's the one. Good luck with the tank

 

Andy

[smiller]

-the RID does not show all bars when full, or if I really top it off to very full, the top bar disappears soon after leaving the gas station.

 

-When nearing empty, the last bar disappears off of the RID long before it used to.

FWIW mine is starting to exhibit exactly the same behavior (1100RT w/ 80k miles.) I think it may be related to the float spending less time in the totally full and nearly empty positions than the mid ranges and thus the internal contacts in the float gauge being more likely to become tarnished in those areas due to lack of use, possibly causing erratic operation.

 

I had my dash off a while ago which involved disconnecting/reconnecting the RID connector but didn't notice any difference in operation of the fuel gauge, but then again I didn't make any concerted effort to clean the connector. Please let us know if that works out for you.

[gusanito]

Mine started doing the exact same thing a few months ago. I gave the electrical connector at the bottom of the tank a good srubbing and it fixed it. Actually stuck a drill bit in each hole and wirebrushed the pins, then recoated with dielectric grease.

 

George

[Joe Frickin' Friday]

FWIW mine is starting to exhibit exactly the same behavior (1100RT w/ 80k miles.) I think it may be related to the float spending less time in the totally full and nearly empty positions than the mid ranges and thus the internal contacts in the float gauge being more likely to become tarnished in those areas due to lack of use, possibly causing erratic operation.

 

Possible, but then the bottom end of the sensor is always submerged in fuel; I wouldn't expect much corrosion/tarnish there, as opposed to at the top (which is nearly always above the liquid level).

 

The symptoms I'm seeing (basically a shift of the whole level scale) is consistent with Andy's description of an additional resistive component in the circuit. (due to corrosion at the RID connector) The sensor gives high resistance when the tank is nearly empty and low resistance when nearly full; the addition of a constant-resistance component would cause the system to report a level lower than the true level.

 

I had my dash off a while ago which involved disconnecting/reconnecting the RID connector but didn't notice any difference in operation of the fuel gauge, but then again I didn't make any concerted effort to clean the connector. Please let us know if that works out for you.

 

Now that I've played with the sensor, I'm gonna ride it for a couple of tankfuls (once the weather warms up ). If no difference (I predict so), then after that I'll pull the dash and clean up that connector and see what happens.

[redryder]

Thanks for the post Mitch. My 02 RT with 55K has been doing the exact same thing for the past 6 months. I figgered that it was just an anomally on my bike. Good (or sad) to see that is more common than I thought. Keep us posted. I'm anxious to see how you fix it. This forum is great! It even helps us fix problems we didn't even know we had

[Tank]

Even 04's with 85,000 miles do it, And I'm a witness.

 

After this thread, i could come to believe TADT

[Alan D]

I had a similar problem on my 2000RT. It was a dirty connector outside of the tank. It's a main connector, on the right side, under the Tupperware. It runs along the fram. There was a picture and description on this board, that's how I found it.

Good Luck

[Joe Frickin' Friday]

I had a similar problem on my 2000RT. It was a dirty connector outside of the tank. It's a main connector, on the right side, under the Tupperware. It runs along the fram. There was a picture and description on this board, that's how I found it.

Good Luck

 

You're right. Jeez, so that's at least three connections with potential problems:

 

-sensor to tank harness

-tank harness to chassis harness

-chassis harness to RID

 

It's amazing this thing works at all!

 

Will check tank to chassis along with chassis to RID.

 

Thanks all for the help.

[Brian PDQ Signs]

Mine has done that since new/used (55K on clock when I bought it - 99RT). Since I'm getting ready to replace the fuel filter I'll check all the connections too! What a timely post

[OlGeezer]

 

You're right. Jeez, so that's at least three connections with potential problems:

 

-sensor to tank harness

-tank harness to chassis harness

-chassis harness to RID

 

It's amazing this thing works at all!

 

Will check tank to chassis along with chassis to RID.

 

Thanks all for the help.

 

Believe it or not, there's one more connection. When my ignition wiring went south because of an over zealous zip tie machine, my fuel gauge worked perfectly when I replaced the wiring harness!!

 

I just had another incident. I think I'm in the mood to replace all the wiring harnesses in my bike before ride it again. Watch "Ride Tales" for the full story.

[Stan Walker]

I measured the resistance at the connector with the float slid all the way up and all the way down the barrel; I measured 4.5 ohms and 77.5 ohms, respectively. The manual doesn't give specs; can someone confirm whether this is correct?

 

The values I have heard in the past were 3.6 ohms full tank and 76 ohms empty. Not measured by me and not on a new unit.

 

Stan

[John in NC]

Please post back with the results and fix. My 04 started doing this too at 25k. I don't know why it bothers me because I still reset the odometer at fill up. The gauge is merely a backup for me.

[Knighthawk]

Mitch,

 

My '04 RT had this problem at about 900 miles. Took it in to have it repaired under warranty. Mechanic told me it was a loose connector in the tank. No problem since.

[KMG_365]

Leslie's 2002 R1150RT (with 128K miles) does it every so often. I clean the main connector on the right (disconnected to remove the tank) with contact cleaner and then pack with dielectric grease when I do the brakes and it's good for another year.

 

"bmwmick" had posted the Ohm numbers in an earlier post, but any increased resistance along the chain will slowly add up over time.