Finally found the time/inclination to get back to the old K today and fit the Peugeot fuel pump as described above, put fresh fuel into the tank and with some trepidation pressed the starter. After a few turns of the engine she fired up and sat ticking over at half fast idle setting but after only a few moments I suddenly realised that there was fuel peeing out of the return pipe junction at rear end of fuel rail ! Turned engine off and retightened jubilee clip at that junction and fired her up again, she started up readily enough and ticked over happily as above (no fuel leak this time). Applied some throttle and it seems that I am back to square one again, starts and responds to throttle normally for a minute or so and then starts farting around. The new fuel pump seemed to be making a little more noise than it ought to which leads me to believe it is working too hard to push fuel around the system and maintain pressure etc. As I do not have access to any type of pressure testing equipment and cannot beg/steal/borrow it just now my instinct is pointing me towards this problem being caused by a faulty FPR (something that I have suspected from the beginning really). I know that the injectors and all the other fuel system components are either new or confirmed good so I guess I am going to have to bite the bullet and get a replacement FPR from somewhere Any thoughts/ideas from the very knowlegeable members here would be welcomed

P.S. I also tried blocking air intake with a rag and performance markedly improved - clearly not a long term cure though. Maybe somebody can make some sense of my ramblings ?

krambo ...you arent hearing that little return valve (in the tank ) making all that noise ? its a common thing and quite disconcerting .

we saw recently that someone changed there air flow meter and had positive results .....but cold well have been that the air bypass setting in the maf was setup wrong and wound almost fully closed on the old unit .

might be worth checking as it sounds like ...as the bike heats up you are getting significant change in mixture ( it seems to me that whilst cold the mixture is enriched by the injection computer ) after which the bypass on the maf takes the major default value .

from what i have read clock wise winds the valve shut ...and anticlockwise a couple of turns is the starting point for mixture adjustment ....with values of 4 or 5 turns out to be around the optimum ,,,,all other things being good .

just make writen details of what you find before adjusting too far huh ?

Thanks for your response charlie99 - it definitely is nothing to do with that pesky return valve as that was removed before I fitted this replacement tank. I guess it is narrowed down to either the MAF or the FPR. When time permits I will run the tests on the MAF sensor as described elsewhere on this forum. My money is on the FPR though I reckon

could be right ....just thought to add what i saw in here

EME is the place for a FPR http://www.euromotoelectrics.com/BOSCH_BMW_Fuel_Pressure_Regulator_13_53_1_464_588_p/boprreg-k588.htm

Thank you for your reply K Freak it is much appreciated even though the link you posted is for a later model K100 than mine. I did search that site however and found the relevant FPR unit for my 1985 K100RT - I can source one in the UK for less than the quoted price on that site but thank you once again for your valued input

Two things to try and advise us on the outcome. If the engine runs do you hear a difference when you open the sump plug? Further, have you got a bicycle pump, one of those with a little pressure gauge? fit that to the return line of the rail (the one going to the FPR) and pump it and see what it does/indicates.

nice test rene ......some times the bleeding obvious escapes us ....

ReneZ wrote:Two things to try and advise us on the outcome. If the engine runs do you hear a difference when you open the sump plug? Further, have you got a bicycle pump, one of those with a little pressure gauge? fit that to the return line of the rail (the one going to the FPR) and pump it and see what it does/indicates.

Thanks for your suggestions ReneZ - I assume that by the sump plug you actually mean the oil filler cap ? I don't have a bicycle pump of the type that you mention - would a foot pump with a pressure gauge do the same job ?

a foot pump would do the job too krambo

Yes to both mate; The running with the oil filler cap simulates runing the bike with an air leak. If you don't hear a difference you have a good airleak.
The air pump will show you that the FPR is working OK by putting a bit of pressure on the fuel line, the right pressure is initially not the most important, the working is.

Thanks to Toto_jp and ReneZ for your replies - I will try what you suggest when time permits and report back with my findings

Update: Today I had an hour to spare so returned to my poor old K100 once again. Having fitted a new fuel pump recently with no change to the poor running problems I had pretty much come to the conclusion that the only thing left that could be at fault was the FPR. Following the advice of a friend and fellow K100 owner I started the bike from cold and all was fine for a minute or two and then the poor running/bogging on application of throttle began once again as expected ! In order to diagnose the FPR I clamped the fuel return line (rear of fuel rail) with mole/vise grips and started the engine once again. I was amazed that after at least five minutes of running the engine continued to respond normally to throttle application thus, in my mind at least, confirming that the FPR was indeed at fault. To verify my findings I then removed the mole grips and started the bike once more, fully expecting the old problem to show up again straight away. However, to my amazement (and puzzlement) the bike continued to respond to throttle application normally for at least an hour of testing, leaving and testing again and the fault appears to have gone ! Can any of the knowledgeable members of this forum explain this puzzle ?

fpr needed a reset ? i imagine it has a spring and piston arrangement internally, it could have stuck open.

not having seen the inside of an fpr ....i imagine that it has a diaphragm to center the piston to the seat .

could this possibly be why we are seeing multiple fpr problems of late ?

(passed use by date and disintegrating components )

charlie99 wrote:not having seen the inside of an fpr ....i imagine that it has a diaphragm to center the piston to the seat .

could this possibly be why we are seeing multiple fpr problems of late ?

(passed use by date and disintegrating components )

@charlie99 - I think you could well be right about the FPR. Maybe my clamping the return pipe and thereby allowing pressure to build normally in the fuel rail made the system function normally as described. Then when I released the restriction, all of a sudden the FPR had to do something and this was just enough to unstick it from its lazy state of being. My money is on having to replace it anyway as a matter of course now - I don't want to be left stranded on my next Europe trip and I am still determined to see the 200,000 miles come up on the odometer before any major rebuild (odometer reading 106,000 just now). This has now become a lifetime ambition type thing - who knows, if I can clock up 200,000 miles then maybe 300,000 is a realistic target for future years ! Thank you for your contribution

im going hunting for a suitable replacement krambo ....out here we dont see so many ....erm european vehicles at the motor recyclers (bosch stuff ) but maybe the ford light vehicle series may have something similar .....in any case glad you found it ....im betting you a happy chappy right about now .....ride well friend ....enjoy

I wonder if you could get one good again by putting it in an ultrasonic cleaner. Regretfully haven't got one here, but most seem to fail on crud etc.

i did a little research on the FPR the other day and yes, they were used in multiple cars like alfa romeo, renault, peugot, opel etc but only bosch available - no cheaper option... i guess the cheapest one i found was around $70... good luck mate!

Thank you for your reply pajonk - I have 3 sources lined up here in the UK:

James Sherlock @ £57.60 GBP

Moto-Bins @ £52.80 GBP

Motorworks @ £58.80 GBP

So it's looking like Moto-Bins gets some more business from me soon.

All of the above are for brand new parts

Sort of makes one think to get one as a spare...

If it matters, Bosch # 0 280 160 200.

Inge K.

you could be right there blakey .....another piece to put in the awesome ducktail bit huh ?

once done should be good for another 25 years huh ?

krambo wrote:

@charlie99 - I think you could well be right about the FPR. Maybe my clamping the return pipe and thereby allowing pressure to build normally in the fuel rail made the system function normally as described. Then when I released the restriction, all of a sudden the FPR had to do something and this was just enough to unstick it from its lazy state of being. My money is on having to replace it anyway as a matter of course now - I don't want to be left stranded on my next Europe trip and I am still determined to see the 200,000 miles come up on the odometer before any major rebuild (odometer reading 106,000 just now). This has now become a lifetime ambition type thing - who knows, if I can clock up 200,000 miles then maybe 300,000 is a realistic target for future years ! Thank you for your contribution

I know a gentleman who has accumulated a million kilometers in a ford escort on one engine. he is a retired ford mechanic and can site torque settings for most parts rote

If you mark it 'solved' in your title the next poor soul with the same problem will know where there's a solution...

club_c wrote:If you mark it 'solved' in your title the next poor soul with the same problem will know where there's a solution...

When I am 100% sure that it is "solved" I will do as you suggest club_c

Good suggestion club_c

G.day All,had a similar problem on my K75 just after I got it.(did not know much about the bricks back then). The engine would start but when throttle applied would bog. It turned out to be the FPR which was replaced and all is fine.Hope that bit of useless info.helps. Cheers Tom Grabau

Tom Grabau wrote:G.day All,had a similar problem on my K75 just after I got it.(did not know much about the bricks back then). The engine would start but when throttle applied would bog. It turned out to be the FPR which was replaced and all is fine.Hope that bit of useless info.helps. Cheers Tom Grabau

So where were you when I needed you ? You could have saved me a whole heap of heartache and head scratching

Sorry Krambo, will pay more attention in the future. Happy riding.Cheers

Update:

Having left the bike alone for 4 days I thought I would fire her up again today and see if all is still well with the old girl. She fired up on the button and responded to throttle normally even after 10 minutes or so of ticking over Should I dare to put all the plastics back on or would that really be "tempting providence" ?

If you leave the tupperware off, nothing will happen.
If you attach it, the bike will play up within a week.

Good work krambo!

blakey wrote:If you leave the tupperware off, nothing will happen.
If you attach it, the bike will play up within a week.

Good work krambo!

Sadly, I fear you may well be right blakey. The law according to sod I believe

As many of you are aware I have been trying to resolve the poor running/bogging under throttle with my 1985 K100RT for some time now (I only get a chance to work on it now and then) ! Well from my previous posts you can follow my diagnostic efforts to date. I had thought that the matter was now closed/solved and was getting ready to mark this thread as "solved". However.......today I decided that the only true way of seeing if the fault had gone would be to actually road test the bike! This turned out to be interesting... All of my previous testing/diagnostics have been done in the garage where the bike has been sitting parked and in a state of undress since I took her off the road some 9 or 10 months ago. So I fitted the bare minimum of necessary bits back on, fired her up (running normally at this point) and started to wheel her out of the garage - she didn't want to leave it seems as I could barely move her at all. Turns out that the front disc pads were binding to the discs and a bit of backwards and forwards rocking took care of that. So, with the engine ticking over sweetly I eased out of the yard and onto the road. We set off quite well but within less than a mile it seemed like we were back at square one again, bogging under throttle and generally running like a pig ! Damn and double damn !! Managed to get her back home to the garage and was by this time feeling a bit depressed. As most here will know I had pretty much narrowed the fault down to the FPR being US but was hoping that my clamping the fuel return rail and building up pressure in the line, then releasing the clamp had in fact unstuck the FPR and remedied the fault. (I had already decided that the FPR would be replaced soon as a matter of course) It seems that the fix was only temporary however....hmmmm.
So I decided on one last run through of the symptoms/observations etc. that led me to this point. Removed the tank filler cap assembly so as to get a better view inside the tank, the bike had cooled by this time so I fired her up, got my specs on and pointed my torch into the depths of the tank.
My findings are:
1. On startup engine fires readily and settles into a steady tickover, responds normally to application of throttle, fuel can be clearly seen returning to front left of tank, fuel pump running quietly.
2. After a few minutes of ticking over and me revving the engine (all normal)
3. After 5 minutes or a bit less the engine starts bogging and not responding cleanly to throttle, fuel return flow to tank has stopped completely, fuel pump has got quite loud and sounds like it is working too hard. (Brand new fuel pump fitted 2 weeks ago)

My question now thrown out to the knowledgeable members of this forum is this...

Do the above results confirm that the FPR is undeniably, indisputably and beyond reasonable doubt f**ked/knackered/US/deceased ? Or could there be something else I have missed ?

hmmm hard to put a finger exactly on it ,,,,but certainly sounds like either the fuel pump is suffereing from load restrictions or is just plain had it ...did you replace the fpr yet .....or hoping the issue would just go away ?

charlie99 wrote:hmmm hard to put a finger exactly on it ,,,,but certainly sounds like either the fuel pump is suffereing from load restrictions or is just plain had it ...did you replace the fpr yet .....or hoping the issue would just go away ?

@charlie99

Have edited my post above to confirm that brand new fuel pump just recently fitted, FPR has not yet been replaced as I thought the matter was resolved

ah !!! yes i remember must have had a brain erm hickup ....do the fpr ...i recon, get it out of the way .

I think it was TWB who fitted a pressure gauge in the line and went riding so as to check the fuel pressure under all conditions. With trying to sort bad running after eliminating air leaks and bad plugs/leads/electrical connections then a quick check of fuel pressure will tell one way or another if the problem is in the regulator.
Regards,
K-BIKE

@K-BIKE & charlie99

Thanks to both for your input as always. I do not have access to a pressure gauge of any sort but am now 95% certain that a new FPR will resolve this issue once and for all - I was really just looking for confirmation of my own 95% inkling that the symptoms described point in that direction

Time to jump on this thread and propose some help.

400 years ago, Shakespeare would have asked "to be or not to be"
Now, we ask "too much gas or not enough gas"? Elementary, dear Watson......

If the pump gives up, you won't have enough pressure to return to the tank as the engine will suck all of it and it won't go over the 36PSI to trigger the FRP.
If the FRP is bad, it may prevents the gas to return to the tank and the engine will start to flood.
I see only one solution to diagnose the problem: installing a gauge in line with the fuel rail and measuring the pressure.
You even don't have to start the bike, but just have to power the fuel pump with 12 volts. Looking at the electric diagram, I believe that if you put a +12v to fuse #6, the fuel pump should run without having the engine cranking.



Please report your finding and we'll go from there.

CF

So you did put the tupperware back on then...................

krambo wrote: fuel return flow to tank has stopped completely, fuel pump has got quite loud and sounds like it is working too hard. (Brand new fuel pump fitted 2 weeks ago)

To confirm that it is FPR that is the problem, and not your brand new fuel pump that`s acting up with
to less delivery.

Check if your spark plugs have become black and sooty, if the FPR is stuck you`ll get a very rich mixture.
(probably black smoke from the exhaust too, is my experience with permanent stuck FPR on two different bikes).

Inge K.

Have ordered a pressure gauge from eBay, it was much cheaper than I expected it to be and I wish I had bought one earlier - it hasn't arrived yet but will post my findings when it does - Link below:

FUEL PRESSURE TEST KIT - INJECTOR TESTER GAUGE

I ordered a gauge that goes up to 4 Bar (58 PSI) - that should be plenty shouldn't it ?

good one ....!!

Ok folks, this is where I am now with my FPR diagnostics. My pressure test gauge and connectors arrived this morning so I spliced the gauge into my fuel line between the fuel tank and the fuel rail, tightened all the connections and started the engine. The engine fired up normally as expected and ran steadily for around a minute and a half or so, during this time the gauge was reading somewhere between 30 and 40 PSI (difficult to pinpoint it exactly because needle vibrating a bit but I think we can safely assume 36 PSI approx). During this stage the fuel pump was nice and quiet and no other strange noises etc. were present. After running happily as above for a short while the bike started running lumpy and the smooth throttle response was lost. As you can imagine I was keeping an eagle eye on the pressure gauge throughout ! Just as the engine started to run badly, the needle on the gauge shot off the scale (past 60 PSI) also the fuel pump started howling like a banshee (overworking and one assumes trying to push against pressure in the fuel line ?) As I understand it this pressure should have been regulated/released by the FPR and thus allowed fuel to return to the tank keeping the pressure in the line to around 36 PSI ? (There was no longer any fuel returning to the tank at this time) So, unless I have completely misunderstood the workings of the fuel injection system, this would suggest to me conclusive proof that the FPR has failed and is no longer doing its job properly, therefore requiring replacement with new part. Incidentally, spark plugs were found to be black/sooty after this test, having been cleaned prior to test suggesting to me too fuch fuel being pumped to cylinders !

Forum members thoughts as always are welcomed

I would agree, its just a bit strange that you would suddenly have a full blockage on a pressure regulator, where you pressed it open agains a sprin previously and had it running OK. As per Berts:





If all is connected correctly (???) you wonder how an opened spring loaded valve suddenly closes and stays closed against a way higher pressure. Unless the inner seal is leaking and pressure leaks to the spring side. But then it would also flow back to your last cylinder through the vacuum line.

given what rene suggests ......maybe an additional test might to be to take the return pipe off completly ......block the tank return port with a piece of folded over hose ....and let the return line empty into a plastic bottle ....this might in fact check if there is a blockage occuring in the return valve in the tank instead of the fpr ?

alternativly move the presure guage to the return line after the fpr .



i have read somewhere that folks have removed the spring in the return valve ....to stop the noise from occuring .....i wonder if the ball bearing is sealing on the top retaining washer or something ?

Charlie,

You have a good point about the return valve in the tank. I never heard about it being stuck, but the best test would be to extend the return line (port 2 on the schematic) and drop it on the tank. This way you could run the bike for a longer time (A plastic bottle would fill pretty quickly).

Krambo, You'r on your way to recovery. You just proved that the fuels pump (expensive part) is in working order. As you get the pressure close to 60PSI, it also proves that the internal FPR built in the pump is working fine.

CF

Thanks to all for their comments. Damn - I thought that my test had proven conclusively that the FPR must be the culprit. I have a later model replacement tank on this bike and as far as I know the old ball bearing assembly is not present in this year's tank model. The fuel returns to the tank somewhere near the top left of the tank (looking from the rear of the motorcycle) and as I understand it the old ball bearing system was used on earlier model tanks with a short stub return inside the tank, purely to stop fuel leaking out of the tank when the pipes were removed. I am as always happy to be corrected on this point

P.S. Have just ordered a used (but good) FPR from motorworks for £28.00 GBP. I have ordered many parts from them over the years both new and used and all have proven to be good so far

Link below:

Motorworks

krambo wrote:as I understand it the old ball bearing system was used on earlier model tanks with a short stub return inside the tank, purely to stop fuel leaking out of the tank when the pipes were removed. I am as always happy to be corrected on this point

You are perfectly correct.

Today I finally found some time to fit the replacement FPR I ordered recently. After much faffing around and removing the air box/filter assembly etc. I finally laid eyes on my nemesis (the FPR)! Having skinned a few knuckles and cleaning up the area under the (now removed) airbox assembly, ok I got sidetracked. I could see the beast in all its grimy glory. Removal was not quite as straightforward as I had been hoping, obviously when originally fitted the entire fuel rail was pre-assembled and installed as a whole unit, I managed to get the blighter off and once in my hands I tried blowing/sucking on the various inlets and outlets. Sucking on the vacuum pipe nozzle got me nothing and neither did blowing through it. Next I tried blowing/sucking through both fuel feed nozzle and return nozzle, there was no restriction at all on either and I could easily blow through both - not sure what that means diagnostically but when I tried the same with the new/secondhand replacement FPR I was unable to blow or suck through either. Whilst I was in the area of the rear of the fuel rail I noticed another unit attached to the rail towards the front of the motorcycle which clearly had electrical connections going to it. In true spirit of adventure I investigated this mysterious device (please enlighten me as to what purpose it serves), it looks like a sensor of some sort. I jiggled its wires and one of them promptly fell off in my hand - clearly this wasn't right. Anyways, I figured that all electrical connections should be tightly fitted whatever their purpose so I used the magical cleaning spray so often mentioned on this forum, cleaned and tightened both electrical connections and rehoused them in their rubber sleeve (could this have been my problem all along I pondered ?) and got back to the FPR. At this point I suddenly realised the time and had to rush off and see a lady customer with a poorly computer. I was reeking of oil and fuel but luckily she was very understanding. So, my next task is to reassemble and reconnect all that I have made asunder and see where I stand. All things being equal and if there is a god of old BMW motorcycles and their owners out there somewhere, something I have done/changed/made good will make the old girl run like clockwork again. I have certainly become much more intimate with my K during this period and am mostly enjoying the learning process.

P.S. If anybody can tell me what that unit forward of the FPR on the fuel rail (2 wire connection) is for I would be most grateful.