FUEL TANK SENDING UNIT

[LBump]

WELL, THIS WILL BE MY 3RD SENDING UNIT INSTALLED (BY DEALER) IN A '03 RT1150. THE DASH GAGE IS HALF FULL ON THE BARS UPON FILL UP. AFTER RIDING SOME 60 MILES THE BARS ARE GONE AND I'M LEFT W/ THE ODOMETER... WHAT IS GOING ON WITH THIS HIGHLY ENGINEE RED MOTORCYCLE??! IS THERE ANY ADJUSTMENT...? OR, IS IT JUST A PLUG-IN AND HOPE FOR THE BEST...? ANY INSIGHT AND/OR OPINON WOULD BE HELPFUL.

[PapaJ]

Have you noticed any resistance when you open the fuel tank, especially right after shutting it down? You might have a plugged carbon cannister if you do. They can cause the items inside the tank to do all kinds of crazy things-like stop working.

[John Dickens]

It's certainly not an unknown problem. My R850RT has been like that for 3 or 4 years now. I just live with it.

[AZgman]

WELL, THIS WILL BE MY 3RD SENDING UNIT INSTALLED (BY DEALER) IN A '03 RT1150. THE DASH GAGE IS HALF FULL ON THE BARS UPON FILL UP. AFTER RIDING SOME 60 MILES THE BARS ARE GONE AND I'M LEFT W/ THE ODOMETER... WHAT IS GOING ON WITH THIS HIGHLY ENGINEE RED MOTORCYCLE??! IS THERE ANY ADJUSTMENT...? OR, IS IT JUST A PLUG-IN AND HOPE FOR THE BEST...? ANY INSIGHT AND/OR OPINON WOULD BE HELPFUL.

 

I would check the fuel filter clamps. There is a very tight clearance between the sending unit and the clamps. If screw type clamps or improperly installed FI clamps are used, that could be your problem. You need to move the sending unit across its entire range of motion to check.

[steveg]

don,t forget about the small vent lines that run from the bottom to the top inside the tank . theres barely enough room to get them connected and theres a oring attached to the low fuel light tube that keeps them from interfereing with the float

[ShovelStrokeEd]

Phreak, the float arm you are referring to is for the low fuel light, not the fuel level sensor. That is in a tube along the right/front of the tank. As mentioned, these are frequently damaged by the tank building a vacuum and collapsing the tube.

 

OP, make sure your vent line is free of obstructions and that the solenoid connecting the breather to the charcoal cannister is functioning. The only time the tank is vented to the atmosphere, assuming the original cannister plumbing is connected correctly is via this solenoid. It is only on when the engine is running and the vent goes into the throttle bodies to evacuate the fumes from the tank back into the engine.

[T__]

(snip)-

OP, make sure your vent line is free of obstructions and that the solenoid connecting the breather to the charcoal cannister is functioning. The only time the tank is vented to the atmosphere, assuming the original cannister plumbing is connected correctly is via this solenoid. It is only on when the engine is running and the vent goes into the throttle bodies to evacuate the fumes from the tank back into the engine.

 

Ed, actually that is incorrect.. The tank is always vented to atmosphere through the canister’s charcoal, then out through the vapor cans vent to atmosphere line.. That solenoid is to allow PURGING the vapor recovery can into the intake manifold at above idle conditions & probably after engine reaches a certain temperature..

 

Twisty

[ShovelStrokeEd]

Oops! You're right.

Still might be prudent to check it all though. I had a wee little spider make a nest in my tank vent line once. Plugged the sucker big time and I'm pretty sure it wasn't all that wonderful for the 'pider.

[snod]

If the fuel level display is erratic, I would suspect the electrical connection to the fuel tank. It is at the lower right kinda under the tank. A large four conductor connector. I have had my RID fuel display get "weird" twice, once at about 50k, and again at about 120k. Both times I cleaned that connector with spray electrical parts cleaner, greased with dieletric grease and reassembled. The fuel display again worked perfectly. This four wire connector runs the fuel pump, the low fuel warning light, and the RID fuel gauge. I have also heard reports of similar symptoms when the connector at the back of the RID is dirty or loose. The connector under the tank is easy to get to with the right side tupperwear off. Remove the bolt at the right rear of the tank (be careful not to drop the nut on the back side) and pivot the tank forward. The connector is anchored to the frame on a bracket. I would check it before I removed the sending unit.

[T__]

As mentioned above IF the evap can charcoal/or outlet is plugged,, or the evap can is plumbed incorrectly,, or the evap can vent hose is plugged off (like with a spider, etc) there is a very good chance the fuel sender tube inside your fuel tank is crushed in due to internal tank negative pressure from engine vacuum during the purging process..

 

The dead give away without a lot of testing or checking is a whoosh sound as you open the fuel tank cap after a decent duration ride.. If your bike does that suspect a crushed fuel sender tube inside the tank..

 

You have gone through a few senders now so SOMETHING is wrong with your bike,, be it a plugged evap system,, improper installation,, incorrect evap or vent plumbing..

 

Plugged evap system on the BMW R bike is not uncommon..

 

Twisty

[kioolt]

I'm going to have to agree with snod on this one. The fuel level sender is a float on this bike. The tube that everyone is referring to I believe is only for the low level light. I would believe that from the symptoms and corrective actions that have already been taken (three fuel level senders changed) that it is a connection problem somewhere on the bike. It appears that the problem goes away as soon as the float fuel level sender is replaced. I would then suspect the only connector that is touched at this point. Which is the connector near the right rear of the tank. An ohmmeter will tell you if the fuel level sender is functioning through its full ranch. I don't know the values for the sender since I've never needed to check one. Someone should know the correct values for a full tank and an empty tank.

[Boffin]

I'm going to have to agree with snod on this one. The fuel level sender is a float on this bike. The tube that everyone is referring to I believe is only for the low level light. I would believe that from the symptoms and corrective actions that have already been taken (three fuel level senders changed) that it is a connection problem somewhere on the bike. It appears that the problem goes away as soon as the float fuel level sender is replaced. I would then suspect the only connector that is touched at this point. Which is the connector near the right rear of the tank. An ohmmeter will tell you if the fuel level sender is functioning through its full ranch. I don't know the values for the sender since I've never needed to check one. Someone should know the correct values for a full tank and an empty tank.

 

You got that the wrong way round. The tube is for level, the float for low-fuel light. If you look at the track on the circuit board that the float wipes over you can see that it only has two positions. Next to it is an unused graduated track.

 

Andy

[kioolt]

I stand corrected. I always assummed that it used the float just like my 91 K-bike. I've never really looked at the float slider to see how it was constructed. I thought it was a resistor.

[LBump]

Thanks to all that responded to this problem! I thought the forum would be a good place to start before the installation of another sending unit. I was told by the dealer that it was bad and needed to be replaced... to the tune of $375 or so. Moreover, the dealer didn't mention ANYTHING about any of the suggestions made by the members of this forum. I want to thank ALL! I be looking into the problem soon and report back. Perhaps it will only be a spider... and if it is I'll pay myself $375.

[ShovelStrokeEd]

Itsy, bitsy, spider plugged the vent line with what was probably an egg case which caused a vacuum in the tank which killed the tube in which the fuel level sensor operates. So, still probably $375 or so for parts. Try Chicago BMW for discounted parts, btw.

 

The rest of the stuff is easy to check out on your own.

[PapaJ]

Just so you're aware Beemer Boneyard had a sending unit used for $50.

[DenverWayne]

I recently had my 071200RT repaired, the gas gage had quit, it would not registed. The dealer replaced the sensor and now when filling the tank it registers 3/4 full. They told me to be patient and in two or three tanks if gas it should register full. I wonder??

 

This problem is a frequent issue.

[smiller]

The dealer replaced the sensor and now when filling the tank it registers 3/4 full. They told me to be patient and in two or three tanks if gas it should register full.

What exactly do they expect to change?

[T__]

The dealer replaced the sensor and now when filling the tank it registers 3/4 full. They told me to be patient and in two or three tanks if gas it should register full.

What exactly do they expect to change?

 

Their work load,, just buying time..

 

Twisty

[alexp]

Andy is correct. The tube is the fuel level which shows as bars and the float is only for the reserve light. I had two tubes replaced within a year. They got crushed by the negative pressure inside the tank due to a clogged canister. Every since we start having ethanol added to the fuel, several BMWs here in the island are having the same problem. I’m not saying that is the problem in NJ. The solution is to remove the canister all together and let the tank breath normally. As far as the gauge not showing full, I GAVE UP. I’ve tried everything possible and when I fill up the tank I’m always one bar less from full. I can live with that! I always use my odometer as a backup since I ran out of fuel on a Highway @ 1 AM.

[bmwmick]

Thanks to all that responded to this problem! I thought the forum would be a good place to start before the installation of another sending unit. I was told by the dealer that it was bad and needed to be replaced... to the tune of $375 or so. Moreover, the dealer didn't mention ANYTHING about any of the suggestions made by the members of this forum. I want to thank ALL! I be looking into the problem soon and report back. Perhaps it will only be a spider... and if it is I'll pay myself $375.

 

Kodak guy,

Have you read this thread?

http://bmwsporttouring.com/ubbthreads/sh...true#Post781276

You can measure the float to see if it's working. 4 Ohms Full and 77 Ohms empty. Not much can go wrong with it other than the connections inside the tube.

 

Mick

[LBump]

Thanks for the link... it helped. I really didn't understand why two holes that were drilled...

I will be waiting untill the next service, when the tank will be removed, to check out the problem.

[bmwmick]

I was just cautioning folks NOT to drill holes in the float sending unit tube like Jamie did here: http://www.kmg-365.smugmug.com/gallery/753109/1/33214088#33214069

There is a chance you could break one of the two sending unit wires that run the length of the tube. They are about the thickness of a human hair. I just added instructions for disassembling the sending unit and repairing the 'crushed' area from the inside.

 

Mick