The misfire from hell

[Prokeys88]

Hi all, new to the motobrick forum but not new to bricks.

I have an interesting problem with a 1987 K75 I have and for the life of me I can't figure it out.

The Condition: After warm up on the center stand everything seems fine. Revs fine, no misfire, temps good, batt voltage 12.5-13.25. Take it off the stand and ride thru the parking lot, runs great  (even 2nd gear) everything is fine. Turn around and head back and it starts misfiring from hell... normally ending with me pushing. Once I push it back (30-60 secs) it will fire right up and no misfire present.

Here is a video of the condition https://www.youtube.com/watch?v=IkLmm3SaDXI&feature=youtu.be

Things I have tested/checked.

Fuel
1. All new fuel
2. New fuel strainer
3. New fuel lines
4. Fairly new fuel filter and fuel pump (less that 5k)
4. Verified fuel is flowing to the fuel rail

Electrical
1. Voltage is low at idle 12v dipping to 11.8. High idle voltage is 13.3ish
2. Replaced alternator brushes same voltage condition
3. Changed Alternator-including new voltage regulator (new alt same volt condition present)
4. Spark plugs. In good condition
5. Hall effect sensor cold water test. Passed
6. Freshly bench charged battery (14v) same result.
7. Load tested (advance auto) and battery checks out fine
7. Checked Ignition for corrosion

Vacuum lines

1. Vacuum ports closed/plugged
2. Air box vacuum line seems intact
3. New air filter (normal maintenance)

If voltage was low enough, I could see where it could present a misfire condition but I tested with a fully charged battery and condition was still present.

If it had fouled spark plugs then it should consistently run rough...

If it wasn't getting enough fuel, then running RPMs up on the bench should create a similar consumption condition as driving so it should experience it on the stand.


My suspicion is the injectors are randomly stopping. I have tested disconnecting the injectors when it is "misfiring" and nothing changes (up to 2 injectors at one time). I have also unplugged the injectors while the engine is running "normal" and it seems to simulate a similar condition (2 injectors disconnected). I think this may be the correct direction, but I can't figure out how 2 injectors could randomly stop working only to start working a few moments later...

Any thoughts? What am I missing?

[volador]

1. Check/clean with DE-oxit, the 4-Pin petrol fuel level sender connector. Manipulate pins/socket for a solid connection
What does the level sender base look like inside the tank?
2. Check/clean with DE-oxit/reseat the ICU and ECU connector plugs
3. Check/adjust throttle position switch
4. Syncro throttle bodies
5. Valve adjustment
6. Do a Starter Backspin or Rebuild the Starter
7. Soak injectors in Lacquer Thinner for a few days to clean or send to MrInjector for cleaning
Many threads/videos on injector cleaning. Use new o-rings on reassembly
8. check/clean the Temperature Sensor connector plug located behind the radiator
9. Are spark plugs Bosch X5DC or NGK D7EA with spark plug 5KΩ wires

"2. Air box vacuum line seems intact"
Are you refering to the "Z" shaped Crankcase Breather Vent hose on the engine rear toward left (clutch side)

[Chaos]

try the HES test with a hair dryer cover off

[volador]

5. Hall effect sensor cold water test. Passed

Not familiar with this method. How's it done?

Hall Effect Sensor info

Hall Effect Sensor thread

[Laitch]

I think this may be the correct direction, but I can't figure out how 2 injectors could randomly stop working only to start working a few moments later...

Maybe when the engine runs long enough, just enough heat and vibration is created to disconnect some circuits then slight cooling allows re-connection. It might be helpful to substitute a different electronic fuel injection control unit for comparison—as long as it didn't cost you anything. :giggles You might do what member Filmcamera did with his rough running engine and manipulate the wiring loom to see if you can reproduce the symptom.

When you indicate that the engine "will fire right up and no misfire present," how long does good running last—until you ride off a distance then turn around again?

[daveson]

Everything is good until you turn around.  Sounds like turning the handle bar could be the problem. See if this is consistent. Is it always while turning left?  Or right? Maybe check the wiring as it moves with the handlebar. Try the opposite way first,  than you normally do.

[Martin]

A crimped over fuel return line from the FPR can cause bad running. More evident when running a non OEM line which doesn't had the built in bend where it goes into the tank. The crimp over can be hard to detect as it sometimes only occurs when you push the tank into position.
Regards Martin.

[Prokeys88]

Thanks for the reply!

I have now tried several of these and still have the misfire.

1. Check/clean with DE-oxit, the 4-Pin petrol fuel level sender connector. Manipulate pins/socket for a solid connection (Done)
What does the level sender base look like inside the tank? (I had to rebuild this last year as the new pump was intermittently cutting off... ended up running a new positive wire)
2. Check/clean with DE-oxit/reseat the ICU and ECU connector plugs (will do in a min)
3. Check/adjust throttle position switch (Have a donor k100, so a quick switch of the throttle position sensor, same misfire)
4. Syncro throttle bodies (haven't tried that)
5. Valve adjustment (havent' tried that yet either)
6. Do a Starter Backspin or Rebuild the Starter (not familiar with backspin)
7. Soak injectors in Lacquer Thinner for a few days to clean or send to MrInjector for cleaning (I may switch the injectors from the donor bike and see what happens)
Many threads/videos on injector cleaning. Use new o-rings on reassembly (o-rings are new)
8. check/clean the Temperature Sensor connector plug located behind the radiator (I did have a problem with the temp sensor when I bought the bike... a mouse had chewed the wire. Resoldered and it ran fine. It would fire but not quite start... this is different but it could be sensor?) Maybe I'll check to see if the wire has deteriorated again
9. Are spark plugs Bosch X5DC or NGK D7EA with spark plug 5KΩ wires

"2. Air box vacuum line seems intact"
Are you refering to the "Z" shaped Crankcase Breather Vent hose on the engine rear toward left (clutch side) (Yep... couldn't think of what you called it :) )

[Prokeys88]

Similar to the hair dryer except using water to cool the area.

I really am feeling like it may be the hall sensor.

Not familiar with this method. How's it done?

Hall Effect Sensor info

Hall Effect Sensor thread

[Prokeys88]

Everything is good until you turn around.  Sounds like turning the handle bar could be the problem. See if this is consistent. Is it always while turning left?  Or right? Maybe check the wiring as it moves with the handlebar. Try the opposite way first,  than you normally do.

I thought that as well but I have bent and moved the wire harness all different directions and it doesn't seem to change anything

[Prokeys88]

A crimped over fuel return line from the FPR can cause bad running. More evident when running a non OEM line which doesn't had the built in bend where it goes into the tank. The crimp over can be hard to detect as it sometimes only occurs when you push the tank inti position.
Regards Martin.

hmm I did change the return line... will check that

[stokester]

hmm I did change the return line... will check that

Did you use the pre-formed BMW line?

Gaithersburg, MD? 

Where you you on Sunday for the inaugural Mid-Atlantic Meet-Up on Cobb Island?

[riots100]

I'm would suggest looking in the fuel tank for sediment and crude down around the fuel pump/strainer.  Something similar happened to me where the sediments were collecting on the fuel strainer and impeding the flow of fuel at higher rpms.  Then after sitting, the sediment would fall off the fuel strainer thus allowing for more fuel to flow before it would get clogged up again.

[Chaos]

also water in the gas, it settles to the bottom, gets sloshed around and picked up by the pump and sent to the injectors.  Actually had that happen to me, a couple cans of HEET took care of it.

[Prokeys88]

Did you use the pre-formed BMW line?

Gaithersburg, MD? 

Where you you on Sunday for the inaugural Mid-Atlantic Meet-Up on Cobb Island?

Hmm... probably up under the k75 if I can't get it running :) What's going on on Cobb Island never been there before.

[stokester]

Hmm... probably up under the k75 if I can't get it running :) What's going on on Cobb Island never been there before.

http://www.motobrick.com/index.php/topic,12246.0.html

[Prokeys88]

http://www.motobrick.com/index.php/topic,12246.0.html

cool! Well if I can get it running I may meet up... it's not looking good at the moment tho... :(