fuel tank, fuel pump, fuel level sender and probably more...

[thegingerbeardman]

hi
i have a 1987 k75c, with what are very typical fuel system problems after sitting a long while...  info here on my intro

i'll be doing the aftermarket fuel pump replacement.  in the mean time, lots of things are coming up:

i have found my fuel level sender, in addition to being caked with some kind of odd gunk that isn't rust, is totally unrepairable due to the resistor windings being broken in dozens of places.  i have read a few threads that say it might be part of the fuel pump power circuit so if it's not there, the pump won't work.  is this true?  i think i want to bypass or otherwise delete it for now if i can.

there is a hose going into a check valve in the front left of the tank that i think is the return hose from the fuel pressure regulator.  am i correct?  the hose is cracked and the check valve was full of... something.  i cleaned it out, just want to know if i need pressure rated hose to replace the damaged one or regular low pressure hose will work?

the foam gasket around the gas cap is dust, i think much of that dust is now in the tank as fine particulate contamination.  has anyone come up with a DIY replacement that doesn't deteriorate in such a despicable manner?  maybe cutting one from some rubber gasket material from the local parts store?
 
is there a commonly available O ring for when i replace the fuel sender in the tank? 

i'll post some pics of the carnage later, for now... off to the garage.

[Inge K.]

The resistor windings on the fuel level sender is for a additional level gauge.

The return hose from the FPR has just low pressure, but the hose is preshaped.....
if you use a ordinary hose, it's a good chance that you get a kink on it at the FPR end.

[thegingerbeardman]

inge thanks!
is this not a problem then?


of course i have to clean it, but will it still work for the low fuel light?


just for fun, here is a picture of what's left of the internal fuel hose outer layer:


this is the fuel sender before i started scraping the gunk off.  it is not rust, as underneath is the metal casing in reasonable condition.

[Inge K.]

inge thanks!
is this not a problem then?
of course i have to clean it, but will it still work for the low fuel light?

That is the worst corroded level sender I ever seen.

About the low level warning light, the area inside the red marking is used...the dark area should have no
connection to ground....but the silver area should.

Still, the most important is the connections for the fuel pump.

[rbm]

i have read a few threads that say it might be part of the fuel pump power circuit so if it's not there, the pump won't work.  is this true?  i think i want to bypass or otherwise delete it for now if i can.

The fuel level sender/low fuel warning circuits are completely separated from the fuel pump.  They share a fuel-resistant pass-through connector, that is all.





The sender is total rubbish.  However, if the metal parts are still intact, they can still serve the function of providing power to the fuel pump.  I would advise to remove the damaged circuit cards and their associated wiring, leaving just the ground wire and yellow wire to the fuel pump.

[thegingerbeardman]

Rbm that is exactly the info in was looking for. Thank you! 

I am still a bit confused about the low level vs resistor wires but I'll figure it out.. Can't make it any worse right? If it's possible to keep the low level light that would be handy. If not no sweat

For all the carnage in there the fuel pump wires look nearly perfect

[rbm]

Try to read posting #31 this document:  http://www.k100-forum.com/t3349-testing-in-tank-fuel-sender-unit  You'll understand the fuel sender mechanism afterwards.

[thegingerbeardman]

That is quite informative. Thanks.

Just so I am clear on thus: the windings are for a gage that my bike doesn't even have, since i only have the lowbfuel light?

If that is so, was it an optional gage from BMW for some versions?

[racinrich]

my 2 cents, electricity and fuel do not mix well . big bang . new sender be safe. sparks and fuel only in a potato gun!!!

[Zipster]

If that is so, was it an optional gage from BMW for some versions?

There's a fuel gauge on the knee pad of my K1100

[dougo]

Hi there; Listen: don't go with an aftermarket pump. I bought an aftermarket pump, installed it, and my K75 wouldn't start. So.. I got smart and went stock. Here is a link to the kit that I bought. It is all stock, and includes everything you need for the fuel pump inside the tank.. mountings etc..rubber sleeve.. I finished installing it, turned the key, pressed the starter button and Vrooom.. immediate gratification. Here's the link:

http://www.euromotoelectrics.com/BOSCH-BMW-K-Fuel-Pump-Kit-16-12-14-61-576-p/fp-576kit.htm

Well worth the money. Now I know I won't have to get inside my fuel tank for a few years.

Doug

[Motorhobo]

I have  fuel pump for a Ford that I paid maybe $50 new. It's been running problem free for at least five years and at least 30k miles. If you install it properly as per the instructions here or on ibmwr.org it will run. The price on the OEM pump is just absurd. So follow the directions and do what your budget tells you - the OEM pump is plug and play but it is 100% incorrect to say that aftermarket pumps don't work.

Once you make the mod you will never have to pay +$300 for a fuel pump again for the useful  life of the bike.


http://www.motobrick.com/index.php/topic,2058.msg10840.html#msg10840

If that is so, was it an optional gage from BMW for some versions?

Frankenduck posted detailed info about this ... It's either here in the Lieberry or on his website but I can't find it again so you'll have to look. Here's info on the fuel level sender from his website - http://www.classickbikes.com/ckb.tech/0.ckb.tech.files/86fls/86fls.htm.

[rbm]

That is quite informative. Thanks.

Just so I am clear on thus: the windings are for a gage that my bike doesn't even have, since i only have the lowbfuel light?

That is correct. 

If that is so, was it an optional gage from BMW for some versions?

Yes, the gauge was optional and available on some models only.  Provisioning of wiring for the gauge was standard on the harness, however.  The Optional Instruments connector is available on post-85 wiring harnesses, meaning that the owner could install gauges at any time.  The connector is on the right side, midway under the tank and looks like an AMP connector you'd find in a personal computer to power a disk drive (if you've ever seen the inside of a PC).

[mjydrafter]

I agree with Motorhobo, no reason to be scared of an aftermarket fuel pump.

Here's a thread I responded to a while a go.  I explain how I fixed my K's fuel pump with an $18 ebay pump.

http://www.motobrick.com/index.php/topic,2058.msg10840.html#msg10840

It's still going strong.

If anyone has trouble finding the Foam piece, let me know, I scored a clearance pool noodle last fall at the WM.  It should be the correct size and is already cored.  It's fancy orange. :hehehe

[thegingerbeardman]

That is quite informative. Thanks.

Just so I am clear on thus: the windings are for a gage that my bike doesn't even have, since i only have the lowbfuel light?

That is correct. 

If that is so, was it an optional gage from BMW for some versions?

Yes, the gauge was optional and available on some models only.  Provisioning of wiring for the gauge was standard on the harness, however.  The Optional Instruments connector is available on post-85 wiring harnesses, meaning that the owner could install gauges at any time.  The connector is on the right side, midway under the tank and looks like an AMP connector you'd find in a personal computer to power a disk drive (if you've ever seen the inside of a PC).

thanks, in the process of trying to preserve the low level light, i kinda ruined the sender.
i should have stopped here, soaked in vinegar for a few hours

more is not better.  the silver plating started peeling.  oh well, it still seals the gas tank i'll just have to watch the odometer like i usually do anyway.


from the very first post i intended to do the aftermarket pump.  i found one for $16 delivered.  i also didn't want to have to buy a rubber isolator and if i was going to delete that anyway, there isn't much point in shimming it with foam either.  so, stealing an idea from the internet and using some scrap titanium from the debris pile, i came up with this:



i did have to buy a new fuel sender O-ring from the dealer, which was $5something and took a day to get.  also had to source fuel hose that is pressure and immersion rated.  the pickings seem slim in the world and if i'd have though a head i could have saved buying on amazon.  SAE 30R10 is the specification that needs to be met, gates 27903 at oriely is $29/FOOT!  18 and change on amazon  haste... waste etc etc

anyway, the bike fired right up after cleaning so onward to the next issue.  thanks for the help ya'll!

[Motorhobo]

Just curious -- isn't the foam also designed as a vibration damper -- which isn't provided by a titanium shim?

[thegingerbeardman]

It is, the part name is Vibration Damper or something similar.

I am sure enough that it is intended to quiet the pump down as opposed to protect then pump from vibration that I am willing to risk deleting it.