Hello all,

This is in regards to a 1992 k100rs.  I've been having some issues with the bike dying on me.  This has happened when it's on a cold start, and today it died on me while I was riding and pulled the clutch in to shift.  The battery still turns the starter nice and strong, so I don't think it's that.

When it dies, I notice that the fuel pump drops out.  When it died on me today while riding it, I noticed a complete loss of electrics (at least at the instruments and pump).  

It was strange.  The electrics then came back as soon as I shifted it from first to neutral (after I had pulled over).  When I tried to start it again, I could hold down the starter button and hear nothing from the fuel pump.  

It eventually came back and I was able to ride on my way.  It feels like it's starved for gas a little bit though.  

I noticed a difference in running maybe a couple weeks ago and it's only worsened to where it is now.  I had originally thought that maybe the injectors were a little dirty even though they've only got around 6-7k miles on them.

I have a fuel pressure gauge hooked in now at the back of the fuel rail.  This was actually my intended question originally: where do I hook up the pressure gauge to test the pump itself?  Which way does the fuel actually flow through the rail.  Front to back? Back to front?  As of right now, everything looks normal.  I do see a drop in pressure as I open up the throttle in to higher RPMs though.  It sits at about 33 psi, and when I open the throttle to around 3-4k rpm, it drops to about 25 psi or so.  I assume that's due to the vacuum connection to the FPR.

I can also hear a number of different sound ranges from the fuel pump.  Being a musician gives me a good ear for what pitch the fuel pump is emitting, and I've noticed it's higher and stronger sometimes, and sometimes it's lower and weaker.

Is any of this a sign of a failing fuel pump?  Could it be anything else?  I've gone through recently (probably 6 months ago) and checked /cleaned all of the electrical connections.

a "T" piece in the fuel pressure line works great

It sounds to me that the problem is electrical. Considering that other things die as well the first place I would be looking is the fuses. Check them all for continuity using a meter not just a visual inspection. These types of fuse are very prone to failure within the plastic casing and I have got into the habit of replacing them every few years.
This is an intermittent problem so also what I have found is that the fuse holder can be failing in that the contacts don't exert enough pressure on the blades of the fuse and so don't contact well.
I recall you doing all the contacts and connectors not too long ago but as often happens the female part of the connector will open up a bit and the same problem as with the fuse holder, not enough contact pressure.
It is almost a catch 22 situation where unplugging and replugging tends to open them up a bit and the circle continues.
Giving the plugs a wriggle while the bike is running can be difficult but often will show the problem up.

If the instruments go out at the same time that sounds like a flaky ignition switch to me.

Yeah Ignition switch is another place that suffers from the wear and tear as the years pass.

Definitely not ignition switch.  I just went out and wiggled it all around, pulled up, pushed down, idle remained constant.  I was in there a couple months ago to clean it out.  I even added a washer to tighten up the little bit of play in the contacts.



@Klompy, I have mine at the back of the fuel rail, nearest the battery.  Does it matter which where it goes?

@Rick, I just wiggled all the fuses while the bike was idling.  No difference, and they all feel good in their seats.  I'll take them out and test em, but I may as well just replace them too.  They're all 15 amp fuses on the 16v bikes, and I've got hundreds of those things lying around.  I have no idea when they were last replaced, and the guy that had this bike last didn't deserve to have it.

I also wiggled the key ignition (the bottom of it) all around while the bike was idling.  No difference.

If the issue is in the internals of the 61322305292(#3) then I don't think jiggling the key would make a difference.






Can't hurt to clean check the battery and ground connections.

When you lose power to the pump etc. does the speedo stop working?  If it still works the Motronic relay is where you will find the problem or the wiring to and from it.  Most likely the Green/yellow wire that feeds power to the motronic unit and the tacho and various lights on the cluster.

Sounds like the ignition switch to me also.  I had the whole cable go up in flames at 70MPH. 


I lost everything then some came back and then it all went in flames.

Have you had the tank off and looked at the connectors underneath?

The very fact you shifted gear meant you pulled on the clutch cable that runs near the cables behind to clocks...well worth a look i'd say.

Mike

@Rick: The instrument needles were still working when I lost power.  I'm not sure if I lost the lights in the instruments as it was day time.  I'll take a look at that wire when I get a chance.  I also went through and tested the resistance of all of the fuses.  6 out of 7 of them said 1.0 ohms.  The 7th originally said 7.6 ohms repeatedly, but when I came back to it again after the others, it read 1.0 ohms like the others.  I wonder if that could have caused it?  Does know which fuse is which on the 16v k100?  The cover for the fuses lists them like this (f8 and f9 have nothing):

F1
F2
F3
F4
F5
F6
F7
F8 - empty
F9 - empty


@Mike: That would certainly make sense, I'll take a look.  What do you mean by clocks; instruments? (sorry)

1-      Instruments, heated grips, brake light, BMU
2-      Parking & tail light
3-      Flasher relay, clock
4-      Powerlet socket, optional alarm
5-      Motronic & relay
6-      Fuel pump relay
7-      Flasher relay, radiator fan, horn

On my 16V, N0 9 Grub screw in the drawing above was missing. Gave some very strange symptoms including not starting. Once grub screw replaced everything worked perfectly

Could also be a idea to check the sidestand switch and its connector.
(cuts the signal to the fuel pump).

... relay. LOL.

duck wrote:... relay. LOL.

?

RicK G wrote:

duck wrote:... relay. LOL.

?

The side stand switch cuts the signal to the fuel pump RELAY from the Motronic, not the fuel pump.  I was just yanking Inge's chain.

Rabidchiwawa007 wrote:@Rick: The instrument needles were still working when I lost power.  I'm not sure if I lost the lights in the instruments as it was day time.  I'll take a look at that wire when I get a chance.  I also went through and tested the resistance of all of the fuses.  6 out of 7 of them said 1.0 ohms.  The 7th originally said 7.6 ohms repeatedly, but when I came back to it again after the others, it read 1.0 ohms like the others.  I wonder if that could have caused it?  Does know which fuse is which on the 16v k100?  The cover for the fuses lists them like this (f8 and f9 have nothing):

F1
F2
F3
F4
F5
F6
F7
F8 - empty
F9 - empty


@Mike: That would certainly make sense, I'll take a look.  What do you mean by clocks; instruments? (sorry)

That erratic reading is exactly what I meant about those fuses.  It could well be that the fuse is the problem but unfortunately as with most intermittent electrical problems you are only sure it is fixed when the problem doesn't occur for the next 100000miles.
If the speedo needle was still working but not the tacho it would narrow it to the motronic relay but as both were working it makes for a far wider search area.

@Ringfad: I looked under there for that No. 9 grub screw, but I don't see anything.  There's no screw and there's no spot for a screw anywhere in that area.

@Rick: Tough to tell if the tach was still working as every time it has happened it's been either at idle or with the clutch pulled in. That makes the engine die and show 0 rpm anyways.

@Inge: one of the first things I did when I had an inkling of an issue with the side stand switch was take it out and splice the wires together as one.  Checked it, still good.

After taking the fuses all out, testing them, and putting them back in, it seems to be running a little better.  It feels better while I ride it, and it hasn't died on me in a couple days.  We'll see how long that lasts.  At this point, I probably just have to wait for it to happen again.  Could it be worth it to check in on the fuel pump relay as well?

In looking at the fuel pressure, I find that while cruising around 75mph on the freeways, the gauge needle flips back and forth between 24 psi and ~48 psi almost faster than the eye can see.  As soon as I let go of the gas, it stabilizes at around 27 psi.  I know there is going to be some fluctuation due to the vacuum hose connection, but is that much of a fluctuation normal? (The fuel pressure regulator has around 9k miles on it).

That grub screw is hidden under a dab of red paint that you have to pick away in  order to see it.

Ah, I see.  I found it.  It was covered in dirt.

So it seems that cleaning and replacing the fuses and some grounds has helped this issue.   It hasn't died on me in a few days, whereas before it died on me at least once a day.  Fuel pressure is good, engine runs good again, looks like everything is go..... EXCEPT I think I should make a new thread for this..  Look for "Transmission Death" in the forum