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Discussion Starter · #1 ·
Alright, gonna try to lay out EVERYTHING that I've observed, then state my theories and ask my questions at the end.

1999 K1200RS, 38000 miles I think. This bike has been put together from a couple salvage bikes, and I've learned to take nothing for granted. It was 90ish percent done when I got it. BUT, as we will see, TONS of electrical routing and connections were done wrong.

I got everything together and took it out for its first ride on Thursday. It freaking RIPPED... until it didn't.

1. It was really hard to start, didn't want to idle until warm.
2. As I'd roll on the throttle, it would accelerate up to a point and then boom- completely cut all power. Like the throttle was snapped closed, even though I was holding it open. It would not accelerate again until I closed the throttle and opened it again.
3. This happened with NO CONSISTENCY with respect to throttle position, RPM, gear, engine load, time under throttle, or any other variable I can think of.

I got home and started to check a few things.

4. Fuel pressure is good. I took the return line off of the rail and toggled the key, fuel came out of the rail and stopped as soon as the pump stopped. The fuel pump and filter are brand new and the fuel system was DEEP cleaned.
5. The TPS was reset using the WOT procedure like, SO many times.

I suspected the TPS was the culprit, causing the ECU to think the throttle was closing at RPM and cutting fuel. This is its purpose, after all. It was just doing it at inappropriate times, maybe. I borrowed a GS911 from a buddy.
Started investigating the TPS using the GS911, a multimeter, and the clymer wiring diagram.

THE CONNECTORS TO THE TPS AND IDLE ADJUSTER WERE SWITCHED. "Woo-hoo!" I thought. "I'll swap them back and my problems are over!" I thought.

So I did so. And hit the starter. And the starter turned. and turned and turned and turned. And the bike never fired. So I dug in further.

6. I pulled the fuel rail out of the head and hit the starter. NOTHING from the injectors.
7. The idle adjuster takes 12V to pin 2. The TPS takes 5V to pin 2. Big yikes.
8. The GS911 reads the TPS just fine, now that it's hooked up correctly. No fault codes. The realtime values from the GS911 even show that the injectors are getting 3ms pulses.
9. Green wire to the injectors is getting 12V. Strangely... it seems that the yellow wire is ALSO getting 12V?
10. The yellow wire to the injectors is not connected to ground, even when turning the starter.

Did I fry my ECU? What triggers the injectors to fire? I assume it's the ECU switching the yellow wire to ground. The GS911 even says the ecu is giving the injectors the trigger. Any ideas??

Thanks in advance!

49 Posts
Wiring harness connectors to the same too. ECU won't trigger injectors unless it knows it's going round. That sensor tells it that. I believe there are also a couple other sensor outputs that could cause it to cut off the fuel. But I'd have to look into it further.
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