BMW K bikes (Bricks)

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futech

futech
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Been going through the basics of getting her up and running since the previous owner had her sitting for over a year, and just found that the injectors aren’t firing. I pulled the injector rail and confirmed and ran some tests. Fuel pump and regulator seem good since fuel pressure is at the 36psi. Each injector fires when 12V is manually applied, and each connector is receiving a signal when starter is pushed (however each is receiving a 10.8V signal rather than 12V). At this point I figure it’s either the ecu wiring harness, or the ecu itself, but not sure how to test that. Would anything else prevent the injectors from firing? Any suggestions on how to test ecu or ecu harness/connector?

    

chris846

chris846
Life time member
Life time member
A common culprit is the 4-pole connector between the FI harness and the main harness. This is under the rear of the tank, and can be identified by the thick (2.5mm) green with red wires going to it.

Not the only cause, by a long way. But it's where I'd start, that's all.


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The Longest Lunch
    

charlie99

charlie99
VIP
VIP
@futech wrote:Been going through the basics of getting her up and running since the previous owner had her sitting for over a year, and just found that the injectors aren’t firing. I pulled the injector rail and confirmed and ran some tests. Fuel pump and regulator seem good since fuel pressure is at the 36psi. Each injector fires when 12V is manually applied, and each connector is receiving a signal when starter is pushed (however each is receiving a 10.8V signal rather than 12V). At this point I figure it’s either the ecu wiring harness, or the ecu itself, but not sure how to test that. Would anything else prevent the injectors from firing? Any suggestions on how to test ecu or ecu harness/connector?

10.8 is what I see a lot and pretty common on a non running engine ....there are some voltage losses along the path though ....a seriously well charged battery often helps raise that voltage a bit ...and why many folks have failed start processes ...with a low battery voltage ...  they just seem to work much better with a good battery charged as it should be .


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cheezy grin whilst riding, kinda bloke ....oh the joy !!!! ...... ( brick aviator )

'86 K100 RT..#0090401 ..."Gerty" ( Gertrude Von Clickandshift ) --------O%OInjectors not firing / how to test ecu and harness Au-log10

'86 k100 rs.. #######..  "Fred " (f(rame) red ) ( Fredrick leichtundschnell ) - -
bits and pieces from many kind friends across the k100 world ...with many thanks ..
    

futech

futech
active member
active member
Thanks for the suggestions. I cleaned up all the connectors with DeoxIT and waiting on my battery to finish a reconditioning cycle. I also took some ohm readings of the ecu connector pins. Is there a document out there on what those pin readings should be? I’ll update once the battery is fully charged.

    

futech

futech
active member
active member
After reconditioning battery and cleaning the electrical connectors, I rechecked the signal voltage and it increased from the 10.8 to 12.3-12.4. However only a couple of injectors only dribbled rather than producing a full stream like when manual 12v was applied to each injector. The bike was able to start however idled very roughly for maybe about 30 seconds max before dying.

    

duck

duck
Life time member
Life time member
One thing I always do with old Ks that I buy is get the FIs refurb'd:
http://www.mrinjector.us/  - only $17.50 per injector.


Also, The Frog put together this excellent troubleshooting info:
http://www.kforum-tech.com/electrical/EFI/bike-wont-start-EN.htm


__________________________________________________
Current stable:
86 Custom K100 (standard fairing, K75 Belly pan, Ceramic chromed engine covers, paralever)
K75 Frankenbrick (Paralever, K11 front end, hybrid ABS, K1100RS fairing, radial tires)
86 K75C Turbo w/ paralever
94 K1100RS
93 K1100LT (x2)
91 K1
93 K75S (K11 front end)
91 K75S (K1 front end)
14 Yamaha WR250R
98 Taxi Cab K1200RS
14 K1600GT
http://www.ClassicKBikes.com
    

futech

futech
active member
active member
Update: so I got the FIs cleaned and reinstalled but still didn’t fire. (Got a dribble from one) I’m currently charging the battery again to double check whether the voltage was a bit too low. I also went through the troubleshooting guide to see if I could narrow it down more. Looks like pin #2 on the EFI connector isn’t showing any voltage (says I should see 12 v). I also did the pulse test using an LED at the injectors and pin 12 on the EFi connector. The LED seemed to only pulse when I released the start button, rather than pulsing while holding. When hooking up the led at pin 12, it turns on when holding the start button and pulses intensity, but stays on (does not pulse on and off). I have not checked ignition control or hall sensor yet

    

duck

duck
Life time member
Life time member
Have you pulled the fuel filter and tried to blow through it?  The fibers in fuel filters can swell if a bike sits for a while.

NAPA 3032 is only about six bucks and good preventative maintenance anyhow.


__________________________________________________
Current stable:
86 Custom K100 (standard fairing, K75 Belly pan, Ceramic chromed engine covers, paralever)
K75 Frankenbrick (Paralever, K11 front end, hybrid ABS, K1100RS fairing, radial tires)
86 K75C Turbo w/ paralever
94 K1100RS
93 K1100LT (x2)
91 K1
93 K75S (K11 front end)
91 K75S (K1 front end)
14 Yamaha WR250R
98 Taxi Cab K1200RS
14 K1600GT
http://www.ClassicKBikes.com
    

futech

futech
active member
active member
The fuel filter and fuel regulator are new. Did not feel replacing the pump was necessary as I ran a pressure test and it’s at 36 psi. When I put a fully charged battery on today, the FIs very minimally spit upon releasing the start button, but didn’t do anything while holding the start. Hall sensor looks good too,. I’ll be testing the ignition control unit either tonight or tomorrow

    

futech

futech
active member
active member
Update: Finally idling! A little rough idling but hopefully it will smooth itself out. Ultimately the problem was a stupid mistake on my part. When replacing the fuel filter, I must have accidentally switched up the direction that it’s supposed to be in. I thought I was consistent with the previous filter, but maybe that was backwards as well. Whoops! Also the fuel line from pump to filter was a little kinked so I straightened that as well. Checked the ignition control pins while I had the tank off, and all look good accept pin 6 (signal from starter switch) as it was showing 8.5 V instead of the 12v listed. If it continues to run rough, I may go ahead and replace the engine harness
Thanks for the help!!!

    

Laitch

Laitch
Life time member
Life time member
@futech wrote: Also the fuel line from pump to filter was a little kinked so I straightened that as well.
A high-pressure, submersible fuel hose within a tank should resist kinking. Replace the hose with an appropriate length of 30R10 fuel hose.


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1995 K75 73,000 miles
Injectors not firing / how to test ecu and harness Usa-lo10
    

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