Fuel Starvation Issue or what? '87 K75s

kentuvman said:

Thanks Lee - picture shown above shows fuel injector clip not properly secured !

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That's the way it came when I trailered it home and stuck it in the back corner of my shop. Haven't had time to get to it for a couple of years. Thanks for catching that.

98lee said:

That's the way it came when I trailered it home and stuck it in the back corner of my shop. Haven't had time to get to it for a couple of years. Thanks for catching that.

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TPS test shows its operating properly.

Will attach fuel rail tomorrow & new fuel & vacuum line - she's coming together!
Still more cleaning to do - huge improvement from when I first started project & have learned a lot!
Great brainpower amongst forum goers!

Yesterdays and Todays Progress

Okay, yesterday afternoon completed re-installation of fuel rail and injectors are now re-installed, wires attached. Zip tied wire to fuel rail like it was before. Cut new vent hose with spring that runs from fuel pressure regulator to throttle body and reinstalled.

This afternoon, installed European cup, new drain hose, and new fuel hoses that run off fuel pressure regulator. Great suggestion Lee on this cup! Wish I'd known sooner.

The hardest task was getting the hose that goes from the air box to the throttle body plastic housing - after fiddling around for awhile discovered that by pushing both housings towards each other it sealed the gap and I carefully used a long flat bladed screwdriver to tighten her up.

Have discovered having the right tools is the RX for successfully completing a project like this. Also realized tonight that it takes an incredible amount of patience, vision and trust in your abilities to get these tasks accomplished.

I'm not out of the woods yet though! - tomorrow, I'll install the tank and hopefully she starts up w/out incident and runs a lot better than what I'd described at the beginning of this thread. Thinking a combination of a mouse nest in air box, dirty fuel injectors, and possibly not an airtight seal between the air box and throttle body box could have contributed to the problem - we shall see!

If she starts up, plan is to take her for a ride! Will change oil before it gets too cold and check valve clearances - if a good day ahead will balance throttle bodies with my Carb Mate and I do know not to mess with the painted screws on the throttle body!

Screw on hose clamp for 90 degree hose between air flow meter and intake plenum must face straight up so it can be accessed from the top.

That's probably how you did it since you didn't have the radiator out. Others have found that they couldn't access the clamp after installing it from the front and then installing the radiator. You don't want to have to remove the radiator just to change pressure regulator hoses.

Today's Progress - one small setback

Put tank on this afternoon, connected fuel lines including the new cool looking grey fuel line I'd bought from the local BMW dealer - this is the line that goes from the tank to the front fuel rail - anyway, totally my brain fart - tried starting bike and gas was spraying from under the tank. I knew everything was snug and started to realize that cool grey fuel line might not be high pressure Fuel Injection Line.

Called the dealer and the parts woman that helped me could not confirm the fuel line she sold me wasn rated for FI systems - she transferred me to service and the service manger put me on hold and came back to say the fuel line is not for my bike!

Oh well - just another brick in the wall.

I later checked with the pre-existing fuel line that's hard as a rock, and it's rated up to 180 psi.

Had a new piece of fuel line in my parts bin and used it to run from fuel pressure reg to rear fuel rail - got the pleasure of R&R'ing the air box again - 2x in 24 hours

Went to the two big box auto parts stores in the area - 1st stop was NAPA and that was no/go on metric fuel line. 2nd stop O O O OReillys and no/go as I figured.

I'm hopefully just one piece of fuel line away from completing the job. If no local sources, will order it online - from what I can see it's 9mm diameter.

Anyway, that's how the project went today :bang head

Tomorrow's a new day!

The line from the tank to the front of the pressure rail is a specific molded hose. It's not open stock from a roll, and it's not gray.

Thank You, Anton!

Looks like I found the hose I'll be needing . . . live and learn and glad I didn't start a fire! I do have an fire extinguisher in my work area!

Mine were beginning to crack and I had a small drip of fuel around the line. I ordered a replacement fuel line kit from beemerboneyard (have an MOA discount) - much cheaper than just the 1 piece from the gas tank to the rail. The kit has enough to do all of your lines, plus a buddy's. It also comes with new injector-rated clamps.

I MAY have fiigured out why I had a gas smell . . .

There's a reason why people take their bikes to professional mechanics but for unknown reasons, ever since I was a child, I was curious how things work.

With that said, picked up 9/16" Gates FI fuel hose that's really close to 8mm diameter and installed the new hose.

Thought I was all set but guess not - gas started leaking just like yesterday - I pulled the tank back to see where the leak is and it seems to be under the protective foil at bottom of tank.

I've read this sometimes happens to fuel injected bikes with aluminum tanks.

So, given this may be where the gas smell was coming from all along, what are my options to getting the tank repaired? It has nice paint on it - oh boy!

Did I route the fuel feed hoses correctly?

I believe I routed the fuel feed hoses correctly? The clamps I'm using are fuel injector line clamps - it snugged them but not unlike anything I've done in the past.

Rearward fitting on front left of tank is going to front fuel feed? Something in the back of my mind says I may have reversed the hoses . . .

kentuvman said:

I believe I routed the fuel feed hoses correctly? The clamps I'm using are fuel injector line clamps - it snugged them but not unlike anything I've done in the past.

Rearward fitting on front left of tank is going to front fuel feed? Something in the back of my mind says I may have reversed the hoses . . .

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The hoses are correct. I use fuel injection clamps that are tightened with a screwdriver. These aren't the "worm" type, but have a solid band. 5/16ths hose is closer to 8mm and what I use. That may be causing your leak.

roncooper said:

The hoses are correct. I use fuel injection clamps that are tightened with a screwdriver. These aren't the "worm" type, but have a solid band. 5/16ths hose is closer to 8mm and what I use. That may be causing your leak.

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Thanks, Ron - I'm using Fuel Injector clamps - had to leave town for a few days so the "pause" button is pushed on the project.

Surprisingly, in the Clymer manual and searching online, finding a visual pic of fuel tank showing orientation of fuel hoses on front inlets is rare.

Did some thinking and probably I don't have a leak in the fuel tank - maybe a blockage inside fuel rail but there should not . . . never had this problem before but also never removed fuel rail - I think my work is 99% accurate.

When I return, I'll ask a friend for help - I know the fuel pump is working - and the bike ran prior to the job described in this post - the fuel hoses are correct, as are the clamps. Gotta be something minor. I haven't reversed the fuel lines - is it possible that perhaps previous owner had routed the fuel pump hoses in tank backwards so fuel is pumping from most forward fuel nipple on left side of tank instead of rearward? I replaced the hose that was attached to tank that runs to forward nipple on fuel rail but didn't take a picture so not sure if it was forward or aft . . .

Is there a way to "bench test" the fuel system with the tank off - I'm really close . . .

I'm almost sure the return hose is non oem and probably kinked one time too many & cracked - believe I'd replaced a few years back but will order an OEM hose. The existing fuel hose doesn't have the bends in it like picture below.

Re-read Lee's previous post where he says:
"RETURN hose between the Fuel Pressure Regulator and the tank MUST be the factory premolded hose, otherwise it WILL kink when the tank is moved forward into position. 13 31 1 461 011"

Progress Report: Transmission Installed today

After putting some distance between me and the K75, I confirmed the hose from the Fuel Pressure Regulator to the tank is not the OEM hose.

Also confirmed the fuel was spraying due to a small tear in the hose where the pre-molded bend is supposed to be in the OEM BMW hose which I've ordered and expecting to arrive this week.

If anyone is reading this, the hose FI hose goes through a larger rubber hose - what is this supposed to be resting against and is to to prevent engine heat from burning a hole in the hose?

Planning to buy a quick disconnect from Beemer Boneyard just for the line from tank to front fuel rail - that's where the mess begins. I've read the pros and cons and some K owners are pleased with this feature. ONLY CONCERN IS THE DISCONNECT UNIT LOOKS REALLY BIG? IF YOU HAVE ANY INPUT ON ADDING THIS, PLEASE CHIME IN!

Anyway, will keep you all posted on my progress!

The hose from the PR to the tank is not under pressure; do you have the hoses hooked up wrong? Look into the tank and see which outlet is fed by the pump. The hose down to the fuel rail, the rail, and the hose from the rail to the PR are pressurized. After the PR there's just a little bit of pressure from the flow.

I don't recall seeing that thick hose shroud (or anything like it) on any hoses I have replaced or bought. Some models have some foam insulation, but that's different.

AntonLargiader said:

The hose from the PR to the tank is not under pressure; do you have the hoses hooked up wrong? Look into the tank and see which outlet is fed by the pump. The hose down to the fuel rail, the rail, and the hose from the rail to the PR are pressurized. After the PR there's just a little bit of pressure from the flow.

I don't recall seeing that thick hose shroud (or anything like it) on any hoses I have replaced or bought. Some models have some foam insulation, but that's different.

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This hose pictured above ran from PR to front nipple on left side fuel tank. Rear nipple hose connects to front fuel rail.

I've got the tank off & will double check.

Just to confirm, the hose from fuel pump attaches to rear or aft nipple on front left side of tank.

Thanks Anton - much appreciated.

Ken,

The rear nipple on the tank goes to the fuel rail. The front nipple goes to the fuel pressure regulator. It's easy to remember for both sets of nipples on the tank. On the left front of the tank, the hose that comes out in front of the other hose goes to the front nipple. Same on the rear nipples. The hose that goes towards the front of the bike connects to the front nipple (that was before you installed "the cup").

I hate to disagree with Anton, and maybe it's only semantics, but the hose from the fuel pressure regulator to the tank is under some pressure. The pumps, particularly the early 52mm pumps are capable of producing over 80 psi. The regulator cuts that down to 38psi by diverting the excess fuel back to the tank. Admittedly, that excess is only restricted by the size of the hose and the head pressure created by the fuel in the tank, but it is under enough pressure to spray out of any crack in the return hose (just like a hole in a garden hose will leak even if the end of the hose is open). You can usually see the turbulence in the tank, when the bike is running, from the returning fuel from the regulator. The fact that it is not the molded hose means that it was more likely to kink and create backpressure in that line. I think you have found your leak.

Most K75s that I have worked on had that larger diameter foam outer hose (maybe 1 1/4" OD x 6" long). I don't know if it is an anti-chafe or a heat insulation fix. It goes on the section of return hose just inside the frame between the fan and engine.

Just checked the parts fiche. It does not show that outer hose anywhere. I seem to remember it coming already installed in the correct place on the return hose when I bought them in years past, but not lately. Maybe they figured you could use your old one and that way they could manufacture the return hose for less. If I get a chance tomorrow, I'll see how many of the six Ks in my shop have it.

At one time I was thinking of putting quick disconnects on the fuel hoses. I remember getting a set of used factory ones and rejecting the idea because I didn't see a clean way of doing it given the room and the shortness of the hoses. That's not saying that it CAN'T be done. I just didn't see a satisfactory way of doing it at the time.

Thanks Lee - I'll double check routing inside tank but believe it's correct.

Will check in once new hose arrives, is installed, and when I have a chance to start the bike.

Ken,

Back to your original problem; a kinked return hose from the regulator to the tank COULD cause the fuel pressure at the injectors to rise. This would be more noticeable at low rpm/low speed/idle, and have less adverse affect at higher rpm/speed. But, I don't see how it would come and go other than being affected by altitude (worse at high altitude, better at low altitude), but that would have to be several thousand foot difference.

98lee said:

Ken,

Back to your original problem; a kinked return hose from the regulator to the tank COULD cause the fuel pressure at the injectors to rise. This would be more noticeable at low rpm/low speed/idle, and have less adverse affect at higher rpm/speed. But, I don't see how it would come and go other than being affected by altitude (worse at high altitude, better at low altitude), but that would have to be several thousand foot difference.

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We'll soon find out!