86 K75C fuel pump problem?

Ok, Houston... we have a problem (although, technically, I'm in Portland).

I took the K75 out for day ride around Mt. Hood a couple of days ago, everything was great (pic attached). As I was pulling into the neighborhood, the bike started sputtering and died. It restarted, but kept sputtering the remaining 1/4 mile. Today, it started fine, and I rode about 2 blocks before it died again. It would restart, but then died as I would engage the clutch. It was acting like it was starving for fuel. Once I got it back home (pushed it... oof!), I turned the key to the on/start position and noticed that I didn't hear the fuel pump hum like I usually do.

Perusing the net, I found forum threads referring to a connector under the tank that could be the culprit, and a fuse... I thought I'd check these before attempting to pull the pump. Does this sound right? Anything else I should consider?

I should mention that the bike sits for much of the year- I ride it during the second half of the summer when I'm up this way. I store it with Stabile in the tank. It's been a solid runner for the two or three years I've had it. Replaced the brake lines with Speigler lines I bought from Ted Porter a few weeks ago (not relevant to the fueling issue I don't think, but the brakes function better).

Jim,

The pump will NOT run by simply turning the key on.

There are only two scenerios in which the pump will run with the key on.

One is the rpm is above the minimum rpm (offhand I don't remember what that is, but it is several hundred rpm) which makes the computer think the engine is running.

Two is when the start button is pressed and for a second or two after. This is what allows the pump to run until the engine starts and then get up to the minimum rpm.


If the pump runs, check the fuel filter.


Get back to us with what you find.

98lee said:

Jim,

The pump will NOT run by simply turning the key on.

There are only two scenerios in which the pump will run with the key on.

One is the rpm is above the minimum rpm (offhand I don't remember what that is, but it is several hundred rpm) which makes the computer think the engine is running.

Two is when the start button is pressed and for a second or two after. This is what allows the pump to run until the engine starts and then get up to the minimum rpm.


If the pump runs, check the fuel filter.


Get back to us with what you find.

Click to expand...

Hi Lee,
OK, thank you for this- I will check and let you know what I find.

Lee,
OK, I did like you suggested and pressed the starter button and released. I could hear the fuel pump hum (briefly), so that's good I think. Is there an easy way to check the fuel filter? Looking at my giant Clymer manual, it looks like I have to siphon the fuel and remove it through the filler cap opening. Good grief..

Jim,

Unless you have a real phobia about touching gasoline, you don't have to drain the tank.


Open gas cap.

Remove four screws that retain gas cap assembly.

Remove gas cap assembly.

Put several layers of towels around opening to protect paint on tank from fuel dribbles.

Note where filter is and routing of hoses so you can get it back in in roughly the same area. A photo helps if you have to wait for a new filter.

Take long screwdriver and loosen the hose clamp on the short hose connected to the fuel filter. (Loosen the clamp on the hose AWAY from the filter, not the one at the filter end.

Pull hose off tube and lift filter out of tank, keeping it over the opening so the fuel dribbles back into the tank,

Disconnect long hose from filter. Leave short hose connected and tight. Drop end of long hose back into tank.

Drain filter from both ends either back into tank or into container on bench.

Wash you hands and maybe put some of your wife's moisturizing lotion on them.

Let filter dry out for a couple hours.

LIGHTLY blow through the filter in the direction of the arrow.

There should be virtually NO resistance. If you are unsure, remove the short hose and lightly blow through that. That is what a clean filter should be like. The amount of resistance is proportional to how trashed the filter is, but partially trashed is still trash.

Short hose goes back on the end of the filter that the arrow is pointing toward.

Don't forget to tighten all hose clamps when you reinstall.

Wash your hands.

Ok, this is very helpful, Lee! I appreciate that- I'll do this tonight and let you know what I find. Thank you again for your help!

Lee,
Ok, so I pulled the filter (easier than I thought, thanks to your help!) and let it dry in the sun. I blew through it and also the short connection tube for comparison, as you suggested. There is a pretty noticeable difference, indicating to me that I need to replace it.

So now the question is, would you recommend I go to the local dealer and buy the BMW replacement filter ($40- they have it in stock), or do you use/trust an aftermarket version I might find at NAPA or O'Reilly's (which are closer to me). I did some poking around online and found this thread (among others), but it seems inconclusive, so I'd prefer to go with your recommendation.

http://forums.bmwmoa.org/showthread.php?43389-K-bike-fuel-filter

Jim,

Personally, I use OEM BMW filters on all the bikes that I work on. Dealer is only 6 miles away.

I just haven't gotten around to properly researching other filters for micron rating, burst pressure, and fitting size.

Other people have said they had good luck with other filters, and in some cases, it is just that, luck. Some of the filters mentioned have lower burst pressures or inadaquate micron ratings.

I'm not saying that there isn't an appropriate replacement. I just haven't looked.

Jim,

I wouldn't hesitate using this filter: http://www.beemerboneyard.com/16142325859.html

And I believe they offer a 10% discount to MOA members.

98lee said:

Jim,

I wouldn't hesitate using this filter: http://www.beemerboneyard.com/16142325859.html

And I believe they offer a 10% discount to MOA members.

Click to expand...

euromotoelectric.com sells mahle & Mann & delivers fast! Order a spare to carry on your bike as you never know when you'll get a bad batch of gas in your tank

98lee said:

Jim,

Personally, I use OEM BMW filters on all the bikes that I work on. Dealer is only 6 miles away.

I just haven't gotten around to properly researching other filters for micron rating, burst pressure, and fitting size.

Other people have said they had good luck with other filters, and in some cases, it is just that, luck. Some of the filters mentioned have lower burst pressures or inadaquate micron ratings.

I'm not saying that there isn't an appropriate replacement. I just haven't looked.

Click to expand...

Ok, thanks Lee. I'll stop by the dealer tomorrow and pick one up. I'll let you know once I've got it installed if it solves my problem! I appreciate your advice and insight.
Jim

98lee said:

Jim,

I wouldn't hesitate using this filter: http://www.beemerboneyard.com/16142325859.html

And I believe they offer a 10% discount to MOA members.

Click to expand...

kentuvman said:

euromotoelectric.com sells mahle & Mann & delivers fast! Order a spare to carry on your bike as you never know when you'll get a bad batch of gas in your tank

Click to expand...

Ok, thank you both! I'll bear that in mind for the future, but I'm only here for a few more days (school starts next week, and apparently they expect me to be there... ) and want to see if I can get it buttoned up before I head back to Texas.

Well... I replaced the filter, buttoned it all up, but no joy. Same symptoms: starts and runs initially (choke on, then off after a minute or two), then will stutter and die (especially if given a little throttle). Hard to restart, and the dies almost immediately. Increasingly hard to restart until it won't restart at all (unless I let it sit for awhile, but then it's the same pattern all over).

It really strikes me as a fuel-related issue (not electrical). I took a short video (sorry for the quality... trying to focus on the tach, but I'm not good at multi-tasking... lucky I didn't fall over trying to do two things at once): https://youtu.be/-6SNOkP_E94.

I'm not sure what to look for from here.

Lee,
I didn't get the moisturizing cream in the divorce, so I thought you might appreciate my hand-protective solution (pic). I washed my hands anyway...

Jim,

Insure that the two vacuum caps on #1 & #2 cylinders are not cracked.
Insure that the crankcase vent hose is not cracked.

Get the bike idleing, then wiggle the tank to frame electrical connector to see if that causes it to stall or miss.

Get the bike idleing, then wiggle the ignition key to see if that causes it to stall or miss.

Get the bike idleing , then wiggle the kill switch to see if that causes it to stall or miss.

Take a voltage reading between the opening in the back of the top fuse and the bolt on the side of the transmission where the ground wire connects by the shift lever with key and kill switch on engine not running.

98lee said:

Jim,


Insure that the crankcase vent hose is not cracked.

Click to expand...

Is that the "Z" hose? If so it's fairly common to have it deteriorate and cause the OP's symptoms.
Also, if I were routinely letting the bike sit for long periods I would get a tank of ethanol free gas for storage.

Bob,

Yes, the crankcase vent hose is the "z" hose.

And yes, bad gas could definitely cause the symptoms noted, even if stabil was used, depending on the original fuel quality and length of storage.

Hi Lee,
I want to say thank you for your help. I ran out of time to figure this out before I had to leave, but will pick it up again when I get back to Portland later this year. I did look at the vacuum caps- they looks to be in good shape and were snug on the fittings. I'll check the remaining items you list when I get back up there.

Bob,
I did fill it with fresh gas after changing the filter while trouble shooting (the tank was low- the low fuel light was just starting to come on), but that didn't seem to make a difference. I had burned through several tanks of gas after taking it out of storage, before this started to occur...

OK, so I'm back at this... so far I have checked:

-the vacuum caps on the #1 & #2 cylinders: OK
-the crankcase vent hose: OK, as far as I can see without removing it (checked with a mirror), although I did snug up the clamps
-with the bike idling, I wiggled both the ignition and kill switches: OK
-I couldn't figure out how to get to the back of the top fuse without removing the tank, so I skipped that step (I may yet come back to it)

At this point, with the bike on the stand, warmed up thoroughly, it seemed to be working (I thought perhaps tightening the crankcase vent hose clamps had solved the problem:roll eyes). Pulled it off the stand, and rode it around the block- worked great.

Decided to take it for a short ride...suited up and off we go... made it about 100 yards and it stalled. Pushed it back to the house. The low fuel warning light was on, so I added 2 gallons of fuel. No joy. Oddly, if I tipped the bike lightly to the right, it would start, idle, and I could rev it somewhat. If I stood it straight or tilted it left, it would die immediately. So, I let it cool. After an hour, it would idle fine again... so:

-checked the tank to frame connector (at least I think I had located the correct one- it runs out from a plate on the bottom of the tank to directly behind the tank, under the seat in front of the tool tray; its a round plug with four or so wires/pins): OK... no miss when wiggled
-while idling, I started wiggling wires somewhat randomly... interestingly, when I move the big bundle of wires (see pic) to the left, the bike would immediately die and not restart. If I move it right, it starts and idles.

So, it seems that I am zeroing in on the problem. I'm not sure what that bundle of wires does, but I see that part of that loom splits off and runs to the fuel injection system, so that make sense (I guess). The question is, now what? Strip the black insulation and look for breaks? Check the plug where it connects to the FI?

Help?

Jim,

That's good news! You now have a repeatable problem that will be easy to locate. It's obviously a bad electrical connection or wire.

Cut the wire ties on that bundle of wire so that you can wiggle each group of wires separately.

Try wiggling the group that goes to the FI computer closer to the computer. If this causes the problem, unplug and reseat the computer plug a half dozen times. When reseating this plug, always hold the backside of the computer so that it does not flex away from the plug. Make sure you hear the retaining clip click each time. Then try the wiggle test again.


PS: By back of the fuse (post 15) I meant the part of the fuse facing you with the amperage number on it. On either side of the amperage number there are slots so that you can insert your voltmeter probe to read the voltage without removing the fuse.