BMW K bikes (Bricks)

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kennybob

kennybob
Silver member
Silver member
Last week i rode my red 88 k75s to bike night and it was sometimes cutting out/bogging as if water in fuel, on the way home ran great.

next morning, no start
So bought a new battery, old one was reading 11.98 while cranking,
but still no start

Went step by step thru CF's master troubleshooting flow chart

checked everything on the flow chart and got to the end where it seemed to indicate the L-jetronic unit, but it was just running the night before?

pulled the fuel rail and there was no fuel spitting out the injectors, some sort of very weak pulsing measured with voltmeter but no real fuel flow.  ? fuel pressure regulator stopping flow => increased pressure and deadhead pump, but hear the pump running and over-run after releasing starter button.?

removed the rail and found rust in the port fittings, rusty stains and gel in the injector screens [thank you ethanol-watered-down fuel].  Cleaned injectors with compressed air and carb cleaner, cleaned rust from rail, put it all back together--no joy.
L-Jetronic computer bugs, fire (ants) in the hole Rusty_13

L-Jetronic computer bugs, fire (ants) in the hole Rusty_12



Next i pulled the jetronic unit out and noticed drain holes in bottom plastic plate were clogged?

Opened the cover of the jetronic and a nest of fire ants came boiling out—lots of eggs and ants, dead ants and dirt.

Cleaned the board and inspected solder joints and traces—no sign of trace damage, a few cold solder joints touched up with hot iron; cleaned board with alkyhawl and it looked brand new.
L-Jetronic computer bugs, fire (ants) in the hole Cold_s10

Put it back in and got the same result—no start, very little fuel squirting out injectors.

Got another jetronic unit and swapped it out—fired up immediately upon hitting the start button!

Maybe need to modify the flowchart to check for bugs in the computer…
L-Jetronic computer bugs, fire (ants) in the hole Ant_eg11

    

RT

RT
Life time member
Life time member
Wow that beats mice eating wiring.
Those ants are a notifiable pest down here, a serious problem imported a few years ago. I read an article that a woman was killed by a nest of them in USA somewhere recently. I hope you put a match to them, see how they like fire, really.
Good luck with it
RT


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2011 R1200RT
    

Dai

Dai
Life time member
Life time member
Yep - looking at the curvature on that board I'd say there's more than one micro-crack somewhere.


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1983 K100 upgraded to K100RS spec, 1987 K100RT
Others...
1978 Moto Guzzi 850-T3, 1979 Moto Guzzi 850-T3 California,1993 Moto Guzzi 1100ie California
2020 Royal Enfield Bullet 500
    

Rick G

Rick G
admin
admin
Yeah i was looking at that thinking it may have been some moisture from the ant nest


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"Man sacrifices his health in order to make money.
Then he sacrifices money to recuperate his health.
And then he is so anxious about the future that he does not enjoy the present; the result being that he does not live in the present or the future; he lives as if he is never going to die, and then dies having never really lived."   Dalai Lama


Bikes 2004 K1200GT 1998 K1100 LT, 1986 K75 GS.
    

Crazy Frog

Crazy Frog
admin
admin
This is an interesting story. I never noticed that there is a drain hole on the unit.
Would it be possible to install a screen to avoid the critters to crawl in the unit?

Years ago, I had install a screen on the snorkel for the air filter. A squirrel was using the canister to store sunflower seeds. It's not good when the seeds are sucked on the air filter and sprouting. (I had that on my cars too)


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L-Jetronic computer bugs, fire (ants) in the hole Frog15L-Jetronic computer bugs, fire (ants) in the hole Logo2101986 k75, 1985 K100rt, 1985 K100rt/EML GT2 sidecar, 1999 K1200lt/Hannigan Astro Sport sidecar.
    

kennybob

kennybob
Silver member
Silver member
Anybody know the function of this ceramic chip-on-board?  It has a black plastic shield that left an air gap above the exposed components--a great hiding spot for more eggs.  It has a clear jelly-like coating and was likely damaged by the nest.
L-Jetronic computer bugs, fire (ants) in the hole Ant_in10

The little 14-pin dip in the foreground is an unobtanium Bosch chip marked '0124'.  It is a multi-vibrator chip that sends the injection command to the base of the drive transistor.  It sends a pulse of pull-in current to turn on the injector solenoids, then drops the current back to a lower hold value, and then cycles the current on and off at the hold value with a squarewave for the duration of the injection pulse width. 

For some reason it is this chip which tends to blow when vehicles with Motronic are connected with jumper cables and somehow reverse the polarity.  Have never found a source for them and have to cannibalize donor boxes to make repairs.

    

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