GS to GSA tank conversion poor fuel transfer

Discussion in 'GS Boxers' started by angtlalaska, Jan 29, 2012.

  1. angtlalaska

    angtlalaska Been here awhile

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    I switched out my 09 1200GS tank for an 10 GSA tank. The 2009 GS tank was different than earlier versions and there is no sucking jet pump nor internal vent lines thus there may be some different instructions being sent to the FPC.

    I purchased a new sucking jet pump, sucking jet tank cover, fuel pump cover, a R1200GSA fuel spider and most every other part that was different between the GS and GSA. The GS fuel pump and fuel pump controller are the same part number so I reused them. Everything went smoothly except for one thing I don&#8217;t seem to be getting sufficient fuel transfer from the right lobe to the left lobe (fuel pump side). Several times I have done the &#8220;Hill Billy&#8221; fuel transfer by laying the bike on its side or rapid acceleration followed by a quick turn and stop. Each time I refuel I am adding at most 6 gallons even though the fuel level shows no bars. I replaced the fuel strip hanger as the GSA part number is different than the GS one and had the fuel strip (same part number) recalibrated. I am not that technical but I would assume that if I am transferring fuel fast enough from the right lobe through the sucking jet pump to the left lobe (side) the fuel strip should show the correct fuel level (remaining) in the tank (left lobe). Since I can tell there is fuel in the right lobe I have to assume I am (the sucking jet pump) not transferring fuel at a fast enough rate. I noticed that the fuel regulator for the GS is 3.5 atmospheres and the GSA is 4 atmospheres. Not a big difference but about 7 psi so I purchased a GSA regulator and installed it. I can&#8217;t see any difference even though I assumed that the sucking jet pump had some back pressure associated with it and the potentially higher pressure would help. It would appear that I am wrong.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:eek:ffice:eek:ffice" /><o:p></o:p>
    Since the FPC controls the speed of the pump and I assume the time the pump runs I have assumed that the timing of the FPC is different for the GS and GSA. If true, that would mean that the ZFE control module (or some other computer setting) is controlling the run time for the FPC. I cannot find anything in the literature that discusses run time signals to the FPC being different for the GS and GSA. <o:p></o:p>
    I have talked to a few guys who have run the by-pass cable for FPC failures and they indicated on their GSA they did not see a difference in operation (fuel level or running out of gas) with the GSA FPC connected or bypassed.
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    I have to assume that the &#8220;third&#8221; wire leading to the FPC is a signal from ZFE to speed up or slow down the fuel pump. I don&#8217;t know how the signal controls the FPC, no power does the fuel pump run flat out or stop. The FPC bypass cable will make the pump run all the time and I assume will cause more fuel to be &#8220;pumped&#8221; from the right lobe to the left lobe by the sucking jet pump. I have confirmed that the sucking jet pump discharge line is well within the left lobe. I have read where several who have done the late model GS to GSA tank conversion have had similar issues although I don&#8217;t recall reading any 09 to 10 tank conversions.
    <o:p></o:p>
    I was reading one of the forums on adding an electronic cruise control to the GS and was impressed with the knowledge some have about the inner workings of the control modules. Tapping into the VVS or ABS to determine speed - wow. Does anyone have any thoughts or ideas on this issue? Thanks for listening.<o:p></o:p>
    #1
  2. Motomochila

    Motomochila Mad Scientist

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    Only thought you have now given me is; forgetting the conversion and trading my 08 GS for a GSA. I have been searching for a tank and just found one on eBay but now after reading your post have decided to ditch that idea. Thanks.....maybe.
    #2
  3. rritterson

    rritterson Been here awhile

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    No direct experience with this on my part, but: I would be curious to know what the flow rate of the sucking pump is when the FPC is bypassed. Presuming that it runs at max rate at in those conditions (and not some "limp-home" trickle rate), and the measured max flow is in spec, then you can eliminate all of the fuel line plumbing and pump setup as the root of the cause and focus your attention on the FPC.

    Given that you can't find any sources that say the FPC needs to be reprogrammed, I'd be inclined to think the problem is something simple and silly, like a partially pinched line, misrouted hose, or fussy electrical connection.
    #3
  4. JoelWisman

    JoelWisman Long timer

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    First things first. Is this a fuel transfer problem or a fuel level sensor problem.

    I've had about 20 of those GSA tanks apart cleaning muck out, removed everything, put it all back together, and took pictures, but first we need to know if there is an actual transfer problem.

    Carry a gallon of fuel in a can and run the tank out. Thats the acid test for if transfer is occurring.
    #4
  5. bigjohn66

    bigjohn66 Been here awhile

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    On my '05 GS (and I think your '10 GSA tank as well) the sucking pump works only from the power of the returning fuel spinning a turbine within the (sucking) pump which spins another rotor which pumps fuel from the right side over to the left. There is no electrical connection from the main fuel pump or controller to the suction pump, it's strictly mechanical. If you're not getting transfer from right to left lobes it's more likely you mis-routed one of the lines on the sucking pump or the rotors are somehow jammed. Do the run-until-empty test first to make sure you're actually not getting transfer and then check out the sucking pump.
    #5
  6. angtlalaska

    angtlalaska Been here awhile

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    Motochila, check to see if your 08 GS has a sucking jet pump. Look at the right side and see if the return line from the fuel regulator runs to the right side or the left side. On the 09, the return goes to the left side and there is no right side fuel cover and therefore no sucking jet pump. I believe that means that the computer is not programed to run the fuel pump through the FPC at a higher speed or longer period of time to cause the fuel to transfer. It is my understanding that on the 09 GS tank the shape was changed to help with water causing FPC issues. If I look at the parts lists 08 GS tanks show a sucking jet pump but at some time in the 09 GS series they don't. It would appear that the issue is within the computer and how it controls the voltge sent to the FPC which in turn controls the speed and or run time of the fuel pump. Look I am way out on a limb here so don't take anything I say about the computer as gospel.

    I have been told some earlier models ran the fuel pump all the time without issues so I know I can run the bypass and get a full transfer. If I can figure out if the lead from the computer to the FPC is zero volts to stop the pump or 12 volts to stop the pump I can design a transfer switch with a diode to prevent flow back to the canbus system to manually move fuel from the right side to the left side. I am hoping someone who understands the computer can provide a work around or knows that when hooked up to the BMW shop computer how you can change the setting to run the FPC at a different rate/time.
    <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:eek:ffice:eek:ffice" /><o:p></o:p>
    I ran into this same problem when I added a TPM to my 09 F650GS using a BMW supplied security/TPM module. The Mother Ship in Germany said even if you buy BMW parts from BMW you cannot change the settings that the computer came from the factory with. So if you don’t buy the option from the factory you can’t add it later. I am hoping BMW isn’t going to say the same thing with changing the settings for the FPC. I know they will not allow the computer to be reprogramed showing 8.7 gallons for a GSA tank over the OEM 5 gallons for the GS tank. If they do not allow the change then I may just add a manual transfer switch like most small or older aircraft have to pump fuel when I am riding.<o:p></o:p>

    Don't dispair you may not have the same issue I had with my 09. At 5' 7" with a 28" inseam a GSA is just not in the cards for me. As it is intown I use a extra low BMW seat and use my Bill Mayer for long trips and really watch where I stop.

    Richard
    #6
  7. angtlalaska

    angtlalaska Been here awhile

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    I think and is possibly part of the problem, that since the 09 GS with its redesigned tank did not have a sucking jet pump the FPC which is controlled by the bike computer based upon speed and power settings, the 09 settings are different than an 08 GS or that of a any GSA which all came with a sucking jet pump. Just a guess.

    #7
  8. angtlalaska

    angtlalaska Been here awhile

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    I am told that the FPC is designed to reduce the volum and time the fuel pump runs to match feul demand from the engine. For thoes bikes with a sucking jet pump that operates on return fuel flow to transfer fuel the FPC is told to run the pump either longer at at a higher rate or both. If I am wrong on nthis point I may have other issues.

    I have run the tank until "dry" only to find out that I only needed 6+ gallons to fill it up. I can see gas in the right lobe so I know I am not getting transfer. I am told that the bike computer through signals to the FPC will cause the fuel pump to run at either a higher rate or a longer time period than is necessary to provide fuel to the injectors. This extra run time or higher rate will cause the sucking jet pump to run at a higher rate or possibly longer time period causing more fuel to be transferred. Since the 09 GS did not come with a sucking jet pump I am told that the bike computer does not consider longer or higher rpm times since the 09 did not need this to move fuel from the right side to the left side. On my 09 GS the return line runs to the left side not the right side. This is why I wnt to the expense of buying a GSA fuel spider with the return line pre-bent to the right side. I also purchased a new sucking jet pump for an 10 GSA tank along with the 10 GSA cover for both left and right so there would be no issues with flow or routing.

    Your points are well taken. I did disconnect the return line and took off the quick connect fitting. I can shoot fuel several feet when the engine is running so I know I am getting flow. Is it the right volume no idea. I still go back to the idea that since the 09 GS tank did not use a sucking jet transfer system which relies on the FPC running the fuel pump at a higher/longer rate than just supplying fuel to run the engine that this ismy problem. But I am open to any suggestions.
    #8
  9. Motomochila

    Motomochila Mad Scientist

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    Still mixed on this subject. My 08 GS only has 16k on the odo, 3k since I bought her in November. The price was way too right Not to acquire her. So now the tank switch issue. Mine has the transfer pump, so will a GSA tank switch work without problems? Even at dealer install price, the total is still a good deal. Or am I going to wish afterwards I had just bought a GSA?
    #9
  10. angtlalaska

    angtlalaska Been here awhile

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    The actual changeover was not difficult so long as you had the correct panels, brackets and so forth on hand. I found that the fuel strip had a different hanger for the GSA vs the GS which means the fuel strip fits into a detent in a different location. The part number was only 1 digit off so be careful when you look at the OEM site. Nobody in the US had the part so it took a week to get one. It’s the small things that can create issues but most are not insurmountable. <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:eek:ffice:eek:ffice" /><o:p></o:p>
    <o:p></o:p>
    It’s also a good time to add a fuse block for additional lights, heated clothing GPS, horn, etc. With the tank off you can run wires in a clean efficient manner. I had a H&B set of crash bars so I had to modify the upper bar to fit the wider tank which to me was the biggest issue because I am not a welder. But it only took a local shop 30 minutes to cut the upper bar and weld in an extension on each side. $50 pretty inexpensive compared to the rest of the parts. I was lucky to pick up a used tank for under $100 which is why I did the exchange. Prior to the tank conversion I used Peg Packers, 2 gal ea and they worked fine on my F650GS and this 1200GS for my travels here in Alaska. I never used the Peg Packer tanks when I drove across the US last November preferring to stop every 200 miles to take a pit stop. There are a few places in Alaska and the Yukon Territory where you need the extra distance. If you are not running two up, there are many options to a GSA tank. That said it would appear that you won't have the same issue that the 09 has without an OEM transfer pump. <o:p></o:p>
    #10