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TrailKlaus

TrailKlaus
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Story time to begin, in two parts: what the previous owner told me, and what I've done and diagnosed so far. 
  According to the previous owner, he had the bike running (after having replaced the fuel pump and probably cleaned/replaced the fuel injectors), and had taken it out for a test drive. He had it idling back it his place, when a fuel injector (apparently not adequately clipped in place) separated enough from the fuel rail to start leaking fuel, from a which a small fire occurred. This somewhat damaged the wiring harness in that area. 
  My efforts: The previous owner gave me a replacement section of wiring harness that I was able to use to replace the fire-damaged sections (being the wiring to the fuel injectors principally). I made sure the fuel rail was squared away and all of the injectors properly secured. I purchased a new battery, changed the oil, and put new fuel in the tank. And then I began trying to crank it up. 
  The electronics power on when the key is turned to on. When the ignition button is depressed, the fuel pump is heard for a second or two, and the starter begins turning the engine over. On my 2nd attempt the end of the hose that returns fuel from the fuel rail to the pressure regulator fissured a let out an alarming jet of fuel (at least I know the system is pressurizing, right?). I replaced the hoses, and kept trying. Essentially the bike sounds like it starts to fire up and then cuts off. I've pulled the fuel rail off and tested the fuel injectors to confirm that they actuate when you press the ignition button. I've also pulled the plugs and verified that they each have a healthy spark. 
  The air flow meter is new me, and I think my current concern is that there is some sensor or system that is, upon startup, sending signals that are effectively shutting the bike down.
  I've also thoroughly cleaned the common ground that is found under the fuel tank. 

There are probably a few other things that I've done to try and diagnose this, but which currently I don't recollect. 

I welcome any thoughts or advice, and I can certainly answer any questions that might provide additional useful information. 

Much thanks!

    

92KK 84WW Olaf

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Does it fire if you are pressing the start button but stop if you release it?


__________________________________________________
1992 K100LT 0193214 Bertha Blue 101,000 miles
1984 K100RT 0022575 Brutus Baja Red 578 bought 36,000 now 89,150 miles
1997 K1100LT 0188024 Wotan Mystic Red 689 58,645 now 106,950 miles Deceased.
1983 K100RS 0011171 Fricka 606 Alaska Blue 29,495 miles Damn K Pox Its a Bat outta Hell Now 40,490 miles. 
1996 K1100LT 0233004 Lohengrin Mystic Red 38,000 miles currently 42,640 miles.

Past:
1968 Yamaha 80 YG1
1971 Yamaha 125 YAS-1
1968 Honda 125 SS
1970 Honda CD 175
1973 Honda CB500-4
Honda CX 500
    

TrailKlaus

TrailKlaus
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@92KK 84WW Olaf wrote:Does it fire if you are pressing the start button but stop if you release it?
It does not continue to fire, even if I still hold down the start button. 
Say I hold it down for 5 seconds. In the first second or so the fuel pump runs, the starter starts cycling the engine, and there is a brief puttering as the engine seems to start to idle. This puttering goes away and the starter just continues to cycle the engine to no effect. 
When testing the spark plugs and fuel injectors, they continued to run/work for as long as I held the start button.

    

Suzi Q

Suzi Q
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Far from certain, but it sounds like your air flow meter isn't 'cutting in' and providing a signal once the thing fires up. Olaf's post is a good diagnostic method based on the fact that pressing the starter button injects fuel. Once you release the starter button (because the engine is now up and running) the flapper valve in the air flow meter should be working enough to call for fuel.
Maybe check the wiring to the AFM - it's part of the same harness that connects the injectors - so if it got damaged in the fire...?


__________________________________________________
Sometimes I'm not really Suzi Quatro.
    

Laitch

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@TrailKlaus wrote:The electronics power on when the key is turned to on. When the ignition button is depressed, the fuel pump is heard for a second or two, and the starter begins turning the engine over.
That starting sequence seems flawed to me. Generally on a 2V moto like yours, the fuel pump isn't heard before the engine starts to crank. It's heard for a couple of seconds after the starter button is released when the engine doesn't start, or if the engine stalls. Your engine could be over-fueling at the start. Fuel pressure needs to be checked with a gauge; the electronics should be tested using the troubleshooting guide here or the LE-Jetronic diagnostic manual.


__________________________________________________
1995 K75 81,000 miles
Troubleshooting a 1985 K100 that won't start/stay running Usa-lo10
    

TrailKlaus

TrailKlaus
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@Laitch wrote:
@TrailKlaus wrote:The electronics power on when the key is turned to on. When the ignition button is depressed, the fuel pump is heard for a second or two, and the starter begins turning the engine over.
That starting sequence seems flawed to me. Generally on a 2V moto like yours, the fuel pump isn't heard before the engine starts to crank. It's heard for a couple of seconds after the starter button is released when the engine doesn't start, or if the engine stalls. Your engine could be over-fueling at the start. Fuel pressure needs to be checked with a gauge; the electronics should be tested using the troubleshooting guide here or the LE-Jetronic diagnostic manual.

Here is a video that I shot at one point, just documenting my attempts to get it running. You can see that the first time it does run, roughly, for a few seconds. The subsequent "starts" are more typical for what I've been experiencing. 

    

Laitch

Laitch
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@TrailKlaus wrote:Here is a video that I shot at one point, just documenting my attempts to get it running. You can see that the first time it does run, roughly, for a few seconds. The subsequent "starts" are more typical for what I've been experiencing. 
I don't hear the fuel pump start when you turn the key to On as you seem to have described, and I don't hear the fuel pump humming for a couple of seconds after the engine stalls, which it should.


__________________________________________________
1995 K75 81,000 miles
Troubleshooting a 1985 K100 that won't start/stay running Usa-lo10
    

92KK 84WW Olaf

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Fuel pump gets signal from 2 places......start button....so that part seems to be good. If in doubt open the gas tank before you hit the start button and should see/hear gas spraying inside the tank.

But engine running it comes from Hall Sensor [HES]. This seems to be not happening.

Although the HES can be the issue K history is that the electrical connections are more common issues so they need checking first. The ICU under the headstock has a big plug, you need to clean the pins, open and clean the connections from the HES into the loom.

You need to be methodical, if for example over fuelling is the issue there are a number of potential causes.

Parts that can cause over fuelling:
ICU under headstock [the electrical connections can also be issue]
MAF Air meter inside the air box [electrical connections can also be the issue]
Temp Sensor behind the radiator [electrical connections can also be the issue]
Injectors staying open too long can come from these
FPR Fuel pressure regulator [no electrical connections, but it has a diaphragm]
This can cause fuel pressure to be excessive= over fuelling.
Vacuum pipes/or vacuum caps failing can also cause this.
Incorrect injectors delivering too much fuel. 


85 Ks some have a vacuum sensor beside the FPR, this has a vacuum pipe the comes from the front of the throttle bodies. If this vacuum pipe fails the vacuum is lost


If you have 2 Ks and one is running correctly you can exchange parts from one to the other, to identify the faulty part, get the bike running a bit quicker and check out the faulty part another time. 

I tend to have lots of spares so usually have a known good unit in the shed to change out and do it one at a time.


__________________________________________________
1992 K100LT 0193214 Bertha Blue 101,000 miles
1984 K100RT 0022575 Brutus Baja Red 578 bought 36,000 now 89,150 miles
1997 K1100LT 0188024 Wotan Mystic Red 689 58,645 now 106,950 miles Deceased.
1983 K100RS 0011171 Fricka 606 Alaska Blue 29,495 miles Damn K Pox Its a Bat outta Hell Now 40,490 miles. 
1996 K1100LT 0233004 Lohengrin Mystic Red 38,000 miles currently 42,640 miles.

Past:
1968 Yamaha 80 YG1
1971 Yamaha 125 YAS-1
1968 Honda 125 SS
1970 Honda CD 175
1973 Honda CB500-4
Honda CX 500
    

TrailKlaus

TrailKlaus
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Thank you Laitch and Olaf! 
I'll work through those areas that you identified, Olaf, and see what sticks. 
Sadly I only have one K, so I can't swap parts to test functionality. Maybe I should just get another K... Smile

    

92KK 84WW Olaf

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If you go at it not using methodology and attention to detail it frustrates the life out of you and can be costly.

Be methodical and its not likely to be expensive and you can learn so much. Use the forum here for best results!


__________________________________________________
1992 K100LT 0193214 Bertha Blue 101,000 miles
1984 K100RT 0022575 Brutus Baja Red 578 bought 36,000 now 89,150 miles
1997 K1100LT 0188024 Wotan Mystic Red 689 58,645 now 106,950 miles Deceased.
1983 K100RS 0011171 Fricka 606 Alaska Blue 29,495 miles Damn K Pox Its a Bat outta Hell Now 40,490 miles. 
1996 K1100LT 0233004 Lohengrin Mystic Red 38,000 miles currently 42,640 miles.

Past:
1968 Yamaha 80 YG1
1971 Yamaha 125 YAS-1
1968 Honda 125 SS
1970 Honda CD 175
1973 Honda CB500-4
Honda CX 500
    

Point-Seven-five

Point-Seven-five
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There is a crankcase breather tube that runs into the airbox behind the throttle position switch.  It is not uncommon for it to be cracked and allowing an air leak.  I would check it if you haven't done so already, before going onto any other troubleshooting.

The tube is about 3/4" in diameter and is a zig-zag shape, hence it's referred to as the Z-tube.  Look for cracks at the hose clamps.  A lot of the more knowledgeable Brick owners usually replace it when they come into possession of a "new" bike.

Because the Brick engine is fuel injected, the throttle should only be opened a small amount.  That is the function of the "choke" lever on the left handlebar.  Since the airflow when starting is so small, cracks in the Z-tube can lean out the mixture enough to make starting difficult if not impossible, and if the engine does start, it will not idle.


__________________________________________________
Present:
1994 K75RT
1991 K100RS
1988 K100RS SE

Past:
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

92KK 84WW Olaf

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How much fuel did you put in the tank?


__________________________________________________
1992 K100LT 0193214 Bertha Blue 101,000 miles
1984 K100RT 0022575 Brutus Baja Red 578 bought 36,000 now 89,150 miles
1997 K1100LT 0188024 Wotan Mystic Red 689 58,645 now 106,950 miles Deceased.
1983 K100RS 0011171 Fricka 606 Alaska Blue 29,495 miles Damn K Pox Its a Bat outta Hell Now 40,490 miles. 
1996 K1100LT 0233004 Lohengrin Mystic Red 38,000 miles currently 42,640 miles.

Past:
1968 Yamaha 80 YG1
1971 Yamaha 125 YAS-1
1968 Honda 125 SS
1970 Honda CD 175
1973 Honda CB500-4
Honda CX 500
    

92KK 84WW Olaf

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If you pull the plugs after that see it they are wet or dry. Do that first. If they are dry you are less likely to be hunting over fuelling. Dud HES can do this, once engine hits 710rpm on start the HES signal runs the fuel pump. No signal no start. As mentioned the connections along the way can cause this too.


__________________________________________________
1992 K100LT 0193214 Bertha Blue 101,000 miles
1984 K100RT 0022575 Brutus Baja Red 578 bought 36,000 now 89,150 miles
1997 K1100LT 0188024 Wotan Mystic Red 689 58,645 now 106,950 miles Deceased.
1983 K100RS 0011171 Fricka 606 Alaska Blue 29,495 miles Damn K Pox Its a Bat outta Hell Now 40,490 miles. 
1996 K1100LT 0233004 Lohengrin Mystic Red 38,000 miles currently 42,640 miles.

Past:
1968 Yamaha 80 YG1
1971 Yamaha 125 YAS-1
1968 Honda 125 SS
1970 Honda CD 175
1973 Honda CB500-4
Honda CX 500
    

14Back to top Go down   Troubleshooting a 1985 K100 that won't start/stay running Empty No go Wed Nov 11, 2020 8:41 pm

daveyson

daveyson
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My first thought when the fuel hose blew  was excessive fuel pressure, unless the clamp was loose.
I'd attach a hose to the front barb of the tank. You should be able to blow air into the tank,  if not the valve might be blocked with rust. Or bypass the valve with a return hose through the filler opening (or into a bucket)  If your brick then goes,  it's a safe bet the return valve is blocked.

Or just remove the return valve that is screwed into the tank. If it's blocked,  clean it well.

Alternatively, it might be the Fuel Pressure Regulator that's blocked. Overfueling could explain why it only runs  for the first few seconds, and only on the first attempt.



Last edited by daveyson on Sat Nov 14, 2020 6:44 am; edited 2 times in total (Reason for editing : That's on a need to know basis (last paragraph))


__________________________________________________
11/1985 bmw k100rt (late model)  Vin. 0090567
 ~120,000 km
    

nino

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Check the ground wires under the fuel tank. Last time I had similar symptoms one of the brown wires was broken. i connected and bike fired up instantly. 
If you removed tank few times there is a possibility of broken wire
Regards

    

TrailKlaus

TrailKlaus
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My apologies for taking some time to get back to this topic. 
I did search out and clean some of the electrical contacts, particularly the ones underneath the tank, and this didn't appear to aid this bike's particular problem. 
I had purchased a fuel pressure testing kit and finally today I got around to putting it to use. I completely drained the fuel tank and put in some fresh fuel. The following video shows how that test went:



Should the fuel pump first run when the key is turned to the "on" position? That's how my 2003 Suzuki SV1000 works, with the fuel pump running for a couple of seconds immediately after the key is turned on, priming the bike to start immediately upon pressing the starter switch. As seen in the video, the fuel pump only comes on once the starter switch is released. Towards the end of the video I feather the starter switch, getting the fuel pump to run and then quickly re-engaging the starter, which gets the bike running (sort of though, as it only stays running for as long as I hold in the starter switch). 
Hopefully this is useful information that might help narrow down what work needs to be done on this bike to get it properly running. 
Thanks!!

    

Point-Seven-five

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A quick press of the start button(not long enough to make the engine turn past top dead center) should make the fuel pump run for about two seconds.  It's hard to tell from the video if that is happening.



Last edited by Point-Seven-five on Sat Feb 13, 2021 11:05 pm; edited 1 time in total


__________________________________________________
Present:
1994 K75RT
1991 K100RS
1988 K100RS SE

Past:
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

Point-Seven-five

Point-Seven-five
Life time member
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Not being familiar with the very early K100 engines this may be a dumb question. I may be operating under incorrect thinking here.

Is it possible you have the engine connected to the fuel tank in reverse? That is, do you have the pressure regulator return connected to the spigot on the tank where the fuel is coming from the pump? Since I have never connected them backwards I can't say how it would affect the running of the engine. I also don't know how to tell which is which on your tank.

What happens if you reverse the two fuel hoses connected to the fuel tank?


__________________________________________________
Present:
1994 K75RT
1991 K100RS
1988 K100RS SE

Past:
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

TrailKlaus

TrailKlaus
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Point-Seven-Five, I'm pretty certain that the fuel lines are connected properly. The fuel pump outlet is sort of front left on the tank, and the line drops down to the front end of the fuel rail. And then on the back end, the return line kind of snakes around the throttle bodies and up under the tank, where it connects to the pressure regulator and then back into the tank itself. 

This bike didn't come to me running, so I have no experience with it actually functioning properly. I would agree that it seems like something is not running when it should. 

I just went back out and tried quick pressing the start button. A single quick press didn't always seem to activate the fuel pump, but if I blipped it a few times (likely causing the engine to rotate past a certain point) the fuel pump kicked on for a couple seconds. So say every three times I blip the start button, the fuel pump comes on. Like passing TDC, or some point, triggers it briefly?

    

Point-Seven-five

Point-Seven-five
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Just for the hell of it, reverse the tank connections and hit the starter for a few seconds.  What does the fuel pressure do?

The more I think about it the more I think something is wrong in your fuel plumbing.  Go through and make absolutely sure everything is as it should be.  You might have a pressure regulator that is backwards, did you look at the check valve where the return line connects to the tank?


__________________________________________________
Present:
1994 K75RT
1991 K100RS
1988 K100RS SE

Past:
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

Point-Seven-five

Point-Seven-five
Life time member
Life time member
The pressure regulator is basically a spring loaded check valve. If you have it connected backwards, it won't let the fuel get to the pressure gauge when the pump is running. That is why I think something is backwards.


__________________________________________________
Present:
1994 K75RT
1991 K100RS
1988 K100RS SE

Past:
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

Laitch

Laitch
Life time member
Life time member
@TrailKlaus wrote:I'm pretty certain that the fuel lines are connected properly. The fuel pump outlet is sort of front left on the tank, and the line drops down to the front end of the fuel rail.
Troubleshooting a 1985 K100 that won't start/stay running Scree125


__________________________________________________
1995 K75 81,000 miles
Troubleshooting a 1985 K100 that won't start/stay running Usa-lo10
    

TrailKlaus

TrailKlaus
active member
active member
Laitch, looking at that image made me realize that I had A. poorly described the fuel line routes, and B. potentially gotten them wrong and hooked them up backwards. I ran outside and checked (perhaps hoping that I had gotten them wrong and switching them back could solve all of my problems), only to find that they were correctly routed, matching the image you shared. Here is a little photo proof: 

Troubleshooting a 1985 K100 that won't start/stay running Bmwk1010

    

24Back to top Go down   Troubleshooting a 1985 K100 that won't start/stay running Empty No go Sun Feb 14, 2021 2:43 am

daveyson

daveyson
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So no pressure with the start button pressed, but once going stops when you release the start button. That's real strange. Are you confident about the rewiring?  

Some quick checks. With a screwdriver to your ear and an injector, you should hear a tick tick tick while cranking.

With a computer safe test light you should have continuous power to pin 86 of the fuel injection relay with ignition on, and continuous earth to pin 85 while the start button is pressed. DO NOT use a normal test light. A computer safe test light would be good to test the hall sensors too.

I'm thinking the fuel pressure drops off too quick too.



Last edited by daveyson on Sun Feb 14, 2021 8:34 am; edited 1 time in total


__________________________________________________
11/1985 bmw k100rt (late model)  Vin. 0090567
 ~120,000 km
    

25Back to top Go down   Troubleshooting a 1985 K100 that won't start/stay running Empty hmmmm Sun Feb 14, 2021 1:06 pm

Paddy1

Paddy1
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Silver member
TrailKlaus,
just a thought... check the plug in connection (between the fuel lines) in the bottom of the tank. they are known to be problematic.
any loose connection? burnt or corrosion?


__________________________________________________
Riding Beemers since 1988
1986 K100RT, 1985 K100RS, 2001 K1200LT, 2004 R1100S, 2004 R1150, 1980 R65, 2014 Zero FX
    

TrailKlaus

TrailKlaus
active member
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@daveyson wrote:Some quick checks. With a screwdriver to your ear and an injector, you should hear a tick tick tick while cranking.
I just took a crack at this (my first time trying the screwdriver to the ear. Took a bit of finagling to make it work) and I got some potentially useful info. While cranking, I'm not hearing any "ticking". When I release the starter, I hear a single clear tick. When I blip/feather the starter (as seen in the video above where I manage to get the bike to stay running (as long as the starter is depressed)), I can hear the ticking become more steady/frequent. 

To Paddy1, I know what you mean about that connection being problematic. It doesn't snap into place, but rather seems to just seat via some friction, which worries me that it could vibrate loose. But currently it appears to be well seated. I believe that I had previously checked the current/resistance on those connections, and they came back with what was expected.

    

Paddy1

Paddy1
Silver member
Silver member
TrailKlaus,
additional comment about that connection.
when cranking... during current draw from the pump any corrosion or loose connection will open as it heats up during cranking and then it will cool when off.
kind of like a fusible link.
this makes it difficult to troubleshoot.
Good luck,


__________________________________________________
Riding Beemers since 1988
1986 K100RT, 1985 K100RS, 2001 K1200LT, 2004 R1100S, 2004 R1150, 1980 R65, 2014 Zero FX
    

28Back to top Go down   Troubleshooting a 1985 K100 that won't start/stay running Empty No go Sun Feb 14, 2021 2:53 pm

daveyson

daveyson
Life time member
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The ICU is supposed to supply earth to the injectors intermittently so that the injectors supply fuel in pulses,  not a constant flow. If there is a short in the earth to the injectors, it will result in flooding. If this is your problem, you might get it running by unplugging the fuel pump electrical plug,  as strange as that sounds. This would be another pointer to overfueling.

This can also be tested with a computer safe, 12 Volt LED, test light. You can probably get one at your local hardware store cheap.

If you can't get it going with the pump unplugged, try again with some revs.


__________________________________________________
11/1985 bmw k100rt (late model)  Vin. 0090567
 ~120,000 km
    

cycleman

cycleman
Silver member
Silver member
It sounds more electrical than fuel pump/regulator related. Normally when you push the start button it activates the pump and then once it starts it keeps running, even when it is released. In your case when you release the start button the pump quits running signalled by the lack of pressure in the fuel rail. Taking a reading of the fuel pressure at either end of the fuel rail shouldn't make any difference. When yours does run it shows the right amount of pressure, so I wouldn't think there is anything wrong with the fuel pump or the regulator.

I would look at anything electrical that is involved in the start circut, including fuses and the starter relay. I also couldn't tell in your pictures if the vacuum hose that goes from # 4 ( from the front of the engine )vacuum bib to the pressure regulator is connected. I also see that the choke/enrichener cable is not hooked up, not likely that would cause your problem.

My vote is for something electrical, including a bad connection.

    

30Back to top Go down   Troubleshooting a 1985 K100 that won't start/stay running Empty No go Sun Feb 14, 2021 6:26 pm

daveyson

daveyson
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Yep I'm thinking electrical problem.

Not happy with my previous reply.

I'll say the pump can be heard for two seconds after the start button is released. The pump is running as long as the button is pressed, plus two seconds, but can't be heard while the engine is cranking.

Let's say the injectors are constantly open with the button pressed, preventing fuel pressure from building. When the button is released the injectors close, then the pump builds pressure in the last two seconds. Maybe.


__________________________________________________
11/1985 bmw k100rt (late model)  Vin. 0090567
 ~120,000 km
    

cycleman

cycleman
Silver member
Silver member
With respect to my previous post. If the vacuum is not hooked to the regulator, the regulator is not going to work and the engine won't start. I mentioned that just because I couldn't see it in his video. Seeing as he had the hoses etc off the regulator or at least hooked up wrong at some point in time, its one of those KISS things. The regulator is purely mechanical, it relies on the engine vacuum to work.The engine has to run to get the vacuum, might explain what's going on.

    

32Back to top Go down   Troubleshooting a 1985 K100 that won't start/stay running Empty check out Mon Feb 15, 2021 12:32 pm

Paddy1

Paddy1
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Silver member
post on forums.bmwmoa.org
interesting info there as well.


__________________________________________________
Riding Beemers since 1988
1986 K100RT, 1985 K100RS, 2001 K1200LT, 2004 R1100S, 2004 R1150, 1980 R65, 2014 Zero FX
    

Point-Seven-five

Point-Seven-five
Life time member
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@cycleman wrote:With respect to my previous post. If the vacuum is not hooked to the regulator, the regulator is not going to work and the engine won't start. I mentioned that just because I couldn't see it in his video. Seeing as he had the hoses etc off the regulator or at least hooked up wrong at some point in time, its one of those KISS things. The regulator is purely mechanical, it relies on the engine vacuum to work.The engine has to run to get the vacuum, might explain what's going on.

Not to start an argument here, but the vacuum line to the pressure regulator isn't necessary to the running of the engine.

The fuel pressure regulator is a spring loaded poppet valve that begins to open when the pressure reaches 35psi.  The spring allows the valve to open enough to control the pressure at 35psi, the more flow there is, the wider the valve opens.  Vacuum has little to no effect on the fuel system pressure under MOST operating conditions.

The purpose of the vacuum line is to lower the regulator's opening pressure, resulting in a lower fuel pressure in the rail supplying the injectors when the bike is engine braking.

The vacuum that results from closing the throttle when decelerating helps open the poppet to reduce the pressure in the rail.  This lower pressure reduces the amount of fuel that goes into the cylinder reducing emissions and helping to prevent backfires.


__________________________________________________
Present:
1994 K75RT
1991 K100RS
1988 K100RS SE

Past:
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

Paddy1

Paddy1
Silver member
Silver member
TrailKlaus,
Have you checked the starter button? almost sounds intermittent.
If the bike sat outside for awhile or high moisture in storage... 
There is a “start” and then a “run” position, looks like you loose it on the run side... 
Boy these things can be a PITA.


__________________________________________________
Riding Beemers since 1988
1986 K100RT, 1985 K100RS, 2001 K1200LT, 2004 R1100S, 2004 R1150, 1980 R65, 2014 Zero FX
    

daveyson

daveyson
Life time member
Life time member
@Paddy1 wrote:
Boy these things can be a PITA.

Too right Paddy.

Hi Paddy, I was thinking that too before my previous post, but then that shouldn't effect the fuel pressure, or in the opposite way, since the pressure drops in start, not run.

But then I'm also thinking the pressure drops too quick.

This is an interesting thread. There's so much weirdness going on here, maybe there's two or more problems happening.


__________________________________________________
11/1985 bmw k100rt (late model)  Vin. 0090567
 ~120,000 km
    

robmack

robmack
Life time member
Life time member
Try this experiment.

  1. Pull Fuse 6
  2. Put a voltmeter between the feed side of Fuse 6 (Green/Red which should be on the RHS when looking at the fuses) and frame ground
  3. Turn on the ignition and press the start button for a couple seconds and release


The expected behaviour is that the engine will crank and the voltmeter will indicate 12V (or so) while the start button is pressed and the engine is cranking. Then, the 12V indication will continue for 2 more seconds after the start button is released.

If you don't see this behaviour, then describe what does happen on the voltmeter.   Replace fuse 6 once the test is finished.


__________________________________________________
Robert
1987 K75 @k75retro.blogspot.ca
http://k75retro.blogspot.ca/
    

TrailKlaus

TrailKlaus
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@robmack wrote:Try this experiment.

  1. Pull Fuse 6
  2. Put a voltmeter between the feed side of Fuse 6 (Green/Red which should be on the RHS when looking at the fuses) and frame ground
  3. Turn on the ignition and press the start button for a couple seconds and release


The expected behaviour is that the engine will crank and the voltmeter will indicate 12V (or so) while the start button is pressed and the engine is cranking. Then, the 12V indication will continue for 2 more seconds after the start button is released.

If you don't see this behaviour, then describe what does happen on the voltmeter.   Replace fuse 6 once the test is finished.
Here's what I got: When I pressed the start button (and the engine began cranking) the voltmeter went to .3 volts. When I released the start button the voltmeter jumped to 12v and held for about 2 seconds before dropping to zero.

    

robmack

robmack
Life time member
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So that's a real problem.  It could be the FI relay, or the ICU or the HES, or the associated wiring.  First off, I'd advise you to stop immediately trying to start the bike in this condition.  You might end up damaging the expensive electronics.  Try and isolate the problem first.

Try this experiment.

Repeat the same experiment I detailed above but this time disconnect the fuel injector wiring harness from the main harness by disconnecting the 5-pin connector along the left frame. Again you'll be measuring the voltage at Fuse 6 and cranking the engine for a couple seconds and release the start button.

If the proper behaviour is exhibited, then the problem is within the fuel injection harness.  Maybe there are shorted wires.  If the same misbehaviour as before is exhibited, then try this.


  1. Keep fuse 6 removed and the fuel injector harness removed
  2. Pull out the FI relay in the relay box
  3. Put the voltmeter +ve lead on pin 86 (Green/Yelllow) in the FI relay socket
  4. Put the voltmeter -ve lead on pin 85 (Yellow/Violet) in the FI relay socket
  5. Turn on the ignition and press the start button for a couple seconds and release


Again, the expected behaviour is that the engine will crank and the voltmeter will indicate about 12V or so while the start button is pressed, and to continue to show 12V for 2 seconds after the button is released.  Describe the results of the test.


__________________________________________________
Robert
1987 K75 @k75retro.blogspot.ca
http://k75retro.blogspot.ca/
    

TrailKlaus

TrailKlaus
active member
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@robmack wrote:Repeat the same experiment I detailed above but this time disconnect the fuel injector wiring harness from the main harness by disconnecting the 4-pin connector along the left frame. Again you'll be measuring the voltage at Fuse 6 and cranking the engine for a couple seconds and release the start button.
I was unable to locate the 4-pin connector. It looks like the fuel injector wiring is pretty seamless all the way back to the main controller/computer. There is a 5-pin connector that it sort of nested up underneath the tank, on the left side, but I don't think you were referring to that one.

    

robmack

robmack
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I changed my posting when I went back and examined the schematic.  It's  a 5-pin, not 4-pin.


__________________________________________________
Robert
1987 K75 @k75retro.blogspot.ca
http://k75retro.blogspot.ca/
    

TrailKlaus

TrailKlaus
active member
active member
@robmack wrote:

  1. Keep fuse 6 removed and the fuel injector harness removed
  2. Pull out the FI relay in the relay box
  3. Put the voltmeter +ve lead on pin 86 (Green/Yelllow) in the FI relay socket
  4. Put the voltmeter -ve lead on pin 85 (Yellow/Violet) in the FI relay socket
  5. Turn on the ignition and press the start button for a couple seconds and release


Again, the expected behaviour is that the engine will crank and the voltmeter will indicate about 12V or so while the start button is pressed, and to continue to show 12V for 2 seconds after the button is released.  Describe the results of the test.
Fuse 6 out, 5-pin connection pulled, FI relay pulled, voltmeter inserted into 86 and 85 as described. 
Success? When I pressed the start button the voltmeter showed about 10.2V, and when I released the start button it climbed towards 12V for a second or two.

    

robmack

robmack
Life time member
Life time member
That is the correct behaviour.  So it means that the HES and ICU circuitry is operational, and by corollary the wiring is intact as well.  I'd concentrate on discovering why the voltage is being dragged down to 0V when cranking.  It seems to me that you haven't yet uncovered all of the wiring damage.  Worth taking a closer look at the harness and connectors for burn damage.  Also disconnect all the plugs on the injection harness and test for inter-wire short circuits that may have happened inside the harness. Also carefully check the main harness on the left side where the fire occurred.  Begin your search starting at the FI relay socket pins 30 and 87 and work out from there towards the injector harness.  Don't forget the FI relay itself.  It might be the cause of the problem  Check it for proper operation.  Remember that it is a 2 Form A (DPST) relay with two 87 terminals and not a 1 Form C (SPDT) relay with a 87 terminal and 87a terminal.

Use a good schematic to do the wire tracing:  https://drive.google.com/file/d/0B3UPbNZRyr1rR3dUOHBhQXp2LXM/view?usp=sharing

Hope you find the problem.


__________________________________________________
Robert
1987 K75 @k75retro.blogspot.ca
http://k75retro.blogspot.ca/
    

TrailKlaus

TrailKlaus
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I thought I would share a video I took back in October (after replacing elements of the wiring harness) where I detached the fuel rail and tested the fuel injectors outside of the bike, in order to visually inspect their performance. 

    

44Back to top Go down   Troubleshooting a 1985 K100 that won't start/stay running Empty No go Mon Feb 15, 2021 10:16 pm

daveyson

daveyson
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It looks to me like it was pulsing fine in October. Think of what have you done since then. I think you replaced the air flow meter. I wonder if it's got a short.


__________________________________________________
11/1985 bmw k100rt (late model)  Vin. 0090567
 ~120,000 km
    

robmack

robmack
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This video gives me an indication that the power feed to the injectors is working, that the ground connections  from the injectors to the ECU are working, that the ECU is getting good power because the injectors are firing, that the signals from the ICU to the ECU are working because the injectors are firing.  Therefore, one can assume that the pin 87 on the FI relay that controls power to all that circuitry is working.  

However, the other pin 87 on the FI relay controls power to the fuel pump and the temperature module through fuse 6 and that part is not working for you. My first suspicion would be the FI relay contacts are not working right.  I don't believe that wire between that pin 87 on the FI relay and fuse 6 is damaged because it is inside the relay box. See if you can find a known good replacement for the FI relay or invest some effort to confirm that the FI relay is either working correctly or is defective.  Maybe you can open the relay and repair it if it proves defective.


__________________________________________________
Robert
1987 K75 @k75retro.blogspot.ca
http://k75retro.blogspot.ca/
    

robmack

robmack
Life time member
Life time member
Try this experiment.

First identify the following two connectors on the FI relay socket 

  •  the pin 87 that leads to the power feed to fuse 6 (Green/Red) 
  •  pin 30 (RED). Be very careful because there is constant power on pin 30 whether the bike is on or not.



  1. Disconnect the 5-pin connector to the injector harness
  2. Pull the FI relay
  3. Make sure Fuse 6 is installed
  4. Take a jumper wire and carefully short pin 30 (RED) on the FI relay to the previously identified FI relay socket connector.


The expected behaviour is that the fuel pump will start to run and will continue to run as long as you maintain the pins shorted.  Remove the jumper and the pump will stop running.

This will verify continuity of wiring between the fuel pump and the suspect pin 87.  If that pans out, then the failing element is most likely the FI relay.


__________________________________________________
Robert
1987 K75 @k75retro.blogspot.ca
http://k75retro.blogspot.ca/
    

Point-Seven-five

Point-Seven-five
Life time member
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Rob, nice analysis.

I would put an ohmmeter on that wire from pin 87 to fuse 6 just to be absolutely sure it's not the problem. Will only take a couple minutes to check.


__________________________________________________
Present:
1994 K75RT
1991 K100RS
1988 K100RS SE

Past:
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

48Back to top Go down   Troubleshooting a 1985 K100 that won't start/stay running Empty No go Tue Feb 16, 2021 12:07 am

daveyson

daveyson
Life time member
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In the hope that this saves a bit of time, I believe the 87 pin closest to the centre of the relay is the wire to fuse 6.


__________________________________________________
11/1985 bmw k100rt (late model)  Vin. 0090567
 ~120,000 km
    

49Back to top Go down   Troubleshooting a 1985 K100 that won't start/stay running Empty No go Tue Feb 16, 2021 3:49 am

daveyson

daveyson
Life time member
Life time member
Jumper wire from 30 to the required 87. This photo is from a previous post which required a fuse for a different purpose.

Troubleshooting a 1985 K100 that won't start/stay running Img_2020


__________________________________________________
11/1985 bmw k100rt (late model)  Vin. 0090567
 ~120,000 km
    

Laitch

Laitch
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I think maybe TK should open the right switch housing and inspect the starter button contacts and the wiring solder joints.


__________________________________________________
1995 K75 81,000 miles
Troubleshooting a 1985 K100 that won't start/stay running Usa-lo10
    

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