BMW K bikes (Bricks)

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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 37,190 miles
1996 K1100LT 0233004 Lohengrin Mystic Red 38,000 miles.
    

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.

    

chris846

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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...?


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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

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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 37,190 miles
1996 K1100LT 0233004 Lohengrin Mystic Red 38,000 miles.
    

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 37,190 miles
1996 K1100LT 0233004 Lohengrin Mystic Red 38,000 miles.
    

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 37,190 miles
1996 K1100LT 0233004 Lohengrin Mystic Red 38,000 miles.
    

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 37,190 miles
1996 K1100LT 0233004 Lohengrin Mystic Red 38,000 miles.
    

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

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))


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11/1985 bmw k100rt (late model)  Vin. 0090567
    

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

    

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