Testing for a defective fuel pump

[Pagman]

Ok, so for those that have been following along with me, I decided to paint my bike and happily did so. Now that I put everything back together, the engine turns but does not want to start! Reason? Fuel is not being pumped into the engine. It's been months since I rode my K.  :bang-head: However, I now believe I have targeted the issue of my problem... the fuel pump. I started by replacing the fuel filter and cleaned the fuel hoses. I then took the connections off the fuel pump and tested both wires with a digital multimeter. I found that the reading stayed at zero unless i hit the start button. When I did, the voltage reading shot up to 11 and even 12 volts sporadically (including decimals). I tried snapping a picture at the highest reading I could while holding the start button. Please let me know if I tested this correctly. If so, then it is the fuel pump that is not delivering the fuel.

I think washing out the tank and maybe shaking out the excess water rattled around some loose debris that was located in the fuel pump. Most likely due to the fuel pump's cracking vibration damper and old brittle fuel hose. Another reason i believe it's the fuel pump is because i don't hear it run when i briefly hit the start button.

So, here I ask: How do i test to see if the fuel pump is ok (just to be sure)? Is there a simple way to clean it out than to dismantle it? What is that little nozzle by the strainer where i placed the arrow?

Thanks, y'all.

[Rick G]

From what I see in the happy snaps your pump is most likely full of crud.
Best test is in the tank with the wires attached,a hose on the outlet then with the hose pointing back into the tank push the start button. You should get a heap of fuel and if your thumb is over the end of the hose then you probably will not be able to prevent the flow (65 psi).
If you dont get that pressure and flow check out the lieberry and see frankenduck's bit about replacing the fuel pump.

[Pagman]

From what I see in the happy snaps your pump is most likely full of crud.
Best test is in the tank with the wires attached,a hose on the outlet then with the hose pointing back into the tank push the start button. You should get a heap of fuel and if your thumb is over the end of the hose then you probably will not be able to prevent the flow (65 psi).
If you dont get that pressure and flow check out the lieberry and see frankenduck's bit about replacing the fuel pump.

I should mention that my tank is currently empty due to working on it. Is there any other way to test the fuel pump, perhaps externally? I just don't want to add fuel then have to dump it out again.

[Rick G]

Any container large enough to hold a couple of quarts (careful of sparks we don't do moon rescues).  don't forget to hold the hose down into the container as you can get a very strong stream if it is ok.

[Scott_]

The nozzle that you marked on the strainer is for the return line hose. IE... there should be a hose connected to the fuel return line at the top of the tank on the inside, then this line is routed down the the basket strainer.

When BMW changed the fuel pump design, they did away with that basket type strainer. When they did that they also removed the internal hose, thus letting the returned fuel just spray wild into the top of the tank.
Since then BMW put out a informational TSB to reconnect a hose to the return line and place the open end of the hose near the fuel pump pickup on the left side of the tank.

As far as testing goes, the pump may have just dried up and is stuck.
Check some of Ducks stickies about fuel pump rehab. I seem to remember him posting about soaking the pump in some FI cleaner for a time to free up the gunk.
To just bump check the motor it really doesn't need to be in any liquid. On a dry bench with no fuel around is pretty safe.
You are afterall just testing it. You aren't trying to drive a cooling fan with it.....

[Inge K.]

Do as Rick says, immerse the pump in a container.........try to run it in both directions,
some have been able to get the crud out of the pump by reversing it.

It would indeed be a good idea to get a new strainer and damper.

The nozzle that you marked on the strainer is for the return line hose. IE... there should be a hose connected to the fuel return line at the top of the tank on the inside, then this line is routed down the the basket strainer.

The strainer is connected to the tank vent.

Inge K.

[Pagman]

Do as Rick says, immerse the pump in a container.........try to run it in both directions,
some have been able to get the crud out of the pump by reversing it.

It would indeed be a good idea to get a new strainer and damper.

The nozzle that you marked on the strainer is for the return line hose. IE... there should be a hose connected to the fuel return line at the top of the tank on the inside, then this line is routed down the the basket strainer.

The strainer is connected to the tank vent.

Inge K.

Regarding the return line hose that you are talking about, is that, and the tank vent, what I have indicated in red in the pictures? The hose was just hanging there and I pulled it off thinking it was useless. I'm now thinking that was probably a mistake. Could not having that hose be the reason why my pump is not working?

[Inge K.]

Your pump should still run, vent hose connected or not.

Inge K.

[frankenduck]

You don't need to immerse it. Just put 12V to the small terminal and ground to the large terminal.  If you hear it spinning then it works. If it "tries" to turn (a soft click and doesn't spin)  then sometimes I've been able to free them up by soaking them in Techron concentrate for a couple of days.

[Pagman]

You don't need to immerse it. Just put 12V to the small terminal and ground to the large terminal.  If you hear it spinning then it works. If it "tries" to turn (a soft click and doesn't spin)  then sometimes I've been able to free them up by soaking them in Techron concentrate for a couple of days.

Frankenduck, good to hear from you again! Ok, so I connected the fuel filter back on the fuel sending unit wires and attempted starting the bike. I heard only the soft click you are talking about, no spin. Everything was connected. I held the starter for a second or two, then after a second or two from releasing the starter, I heard the soft click. Same result each time I tried. When the bike was in use, I was unaware that the filter strainer was ripped in all places and rubber pieces from deteriorated hoses was floating around in the tank. I believe it may have clogged the filter. I will try the Techron concentrate as you recommended. How many days should I attempt this for and what are other options to free up the filter just in case the techron was unsuccesful? Help from anyone is appreciated. Thanks, y'all.

[frankenduck]

I think I soaked it for a couple of days.  I've heard of people taking the fuel pump apart but I never have.

[Pagman]

I think I soaked it for a couple of days.  I've heard of people taking the fuel pump apart but I never have.

I'll do the techron emmersion but is there anything else that can possibly speed up the process? I'd hate to wait a few days just to find out it was unsuccessful. Also, I don't know how successful I would be by dismantling the pump.

[frankenduck]

Soak it for one day.  See if that works. If not, soak it some more.

Since it's stuck I wouldn't use the ignition to test it since that runs it for a few seconds. I'd use some test leads and do it very quickly so you're not stressing the motor much if it's still stuck.

(And point it away from your face.)

[Scott_]

Something else to think about, if your pickup strainer was torn, as you indicate, and you picked up bits of rubber into the pump, the Techron may not disolve them.

[frankenduck]

Something else to think about, if your pickup strainer was torn, as you indicate, and you picked up bits of rubber into the pump, the Techron may not disolve them.

Quite the optimist, aren't you?  :neener:

[Pagman]

A few days ago, I stumbled upon a link where one man shows a step by step instruction (through pictures) on how to dismantle a k bike fuel pump. I can't find the link again. Can anyone link it to me? Thanks.

[Inge K.]

Close to the end in this thread.
Have you tried to reverse the pump yet.

Inge K.

[Pagman]

Close to the end in this thread.
Have you tried to reverse the pump yet.

Inge K.

What do you mean by that?

[Scott_]

Something else to think about, if your pickup strainer was torn, as you indicate, and you picked up bits of rubber into the pump, the Techron may not disolve them.

Quite the optimist, aren't you?  :neener:

Probably a bad side effect of working in a government environment the last 15years.  :loopy:

Inge's idea of trying to run the pump in reverse isn't a bad idea. Might be able to dislodge the offending gunk.

[Pagman]

I'm assuming that reversing the pump means reversing the polarity. I thought something like this would damage a pump, but since my pump is not ideal at the moment, I guess I'll go ahead and give it a shot. Currently, I have the pump soaking in techron concentrate. Hopefully one or the other will work.

[Pagman]

You don't need to immerse it. Just put 12V to the small terminal and ground to the large terminal.  If you hear it spinning then it works. If it "tries" to turn (a soft click and doesn't spin)  then sometimes I've been able to free them up by soaking them in Techron concentrate for a couple of days.

I officially soaked the fuel pump for two weeks in techron concentrate. It had no effect in my case. It's ok though, because yesterday I received my new fuel pump. It's an exact aftermarket replacement that came from england through ebay. Anyway, my K can now pump fuel again... YAY! :eek:

Before I can start riding again, I still have one more issue related to the electrical. I will post that issue in a new thread so I can officially end this one. Thanks everyone for your help.

[MAD]

Hi All,
I'm new to this forum.
As you can imagine, I came across to this forum searching the internet for some help with my BMW K75.

My issue at the moment: the fuel pump stopped working after my motor bike has been sitting still for a year or so with an empty fuel tank.
I managed to disconnect the fuel pump from the fuel tank and test it.
Initially, the fuel pump wasn't working at all, after some gentle tapping to its body, it started working again.
I have tried to test it by submerging the pump in 0.5l of fuel in a small plastic container.
I can hear the fuel pump spinning, but fuel pump is not picking/sending any fuel out.
Am I doing anything wrong? Should the pump be completely submerged in fuel?

Thanks in advance. 

[The Mighty Gryphon]

Here is what I would do if it was my pump. 

Get some fuel system cleaner, about 350ml.  Put the pump upright in a container that is just a little larger than the pump and then fill the container with the fuel system cleaner so the cleaner covers at least half of the height of the pump.  Let it sit for a couple days and then try to run it again. 

When you run the pump make sure the fuel level is at least half way up the side of the pump.  Make sure you have the polarity of the power correct.  Reverse polarity will make the pump run backwards and it won't prime.

[frankenduck]

Make sure you have the polarity of the power correct.  Reverse polarity will make the pump run backwards and it won't prime.

The smaller diameter terminal is 12V. The larger diameter terminal is ground.

[MAD]

Thanks both!
I will try that and see what happens.