BMW K bikes (Bricks)

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futech

futech
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New member
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

"redframe" rs "bitsa"  with many contributions from the k100 community ,,with many thanks
    

futech

futech
New member
New 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
New member
New 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


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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
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