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Thread: Cutting out at high rpm

  1. #1
    We're having an issue with our engine dying at ~11k, and I'm wondering if anyone else has come across similar problems.

    Sometimes we seem to be able to avoid the issue and reach the rev limiter, other times the car will cut. The car is coming to a slow halt, then there's a bang when the car stops.

    I'm wondering if our ECU (Bosch MS4) or our CDI (M&W Pro 14) is the root cause, or if it's a wiring issue. We have a problem with the same symptoms on the dyno, but as our data logger hasn't arrived yet we can't be completely sure they're the same problem.

    We'll be doing some rolling road testing tomorrow to try to find if any particular situations that cause it.

  2. #2
    What engine are you guys using?

    More importantly, what coils?
    Nothing is impossible. Improbable yes. But not impossible.

    Swinburne University of Technology

  3. #3
    It's a 2007 Yamaha R6 and I'm pretty sure they're the coils that came with the engine.

  4. #4
    Looking at those coils on the net (ebay/etc) how do you know that they are CDI coils?

    They look near identical to the cbr 600 coils (f4 - black top denso, RR - blue top denso's), which to the best of my research and knowledge are a hei coil.

    Now, a cdi on a hei coil will work, but it will hit a frequency where it all breaks down.
    Perhaps this is what you are finding.

    Got a spare induction ignition unit (ignitor) or someone with a LS engine (coils have in built ignitors) spare to test the theory?
    Nothing is impossible. Improbable yes. But not impossible.

    Swinburne University of Technology

  5. #5
    The service manual for the bike lists a CDI ignition system

  6. #6
    Hey Boffin,

    Cheers for the replies.

    I've been looking a bit on the net and can't find many references to the CBR on HEI but there are quite a few CDI modules for the CBR for sale on ebay??

    Having never worked with a CBR or an HEI ignition system I'm not in a brilliant position, but I thought that HEI coils had a significantly bigger top (the bit near the connector).

    Tickers, is that the manual for the R6 or the CBR? Have you guys been able to replicate the problem while the car's stationary, or does it only happen at higher loads as on the dyno?

  7. #7
    It might be worth while to but a scope on your crank sensor to see what it is doing on the dyno. It could be possible that your crank voltage thresholds are being exceeded and not crossing a "Zero" for the ECU to recognize the tooth. Therefore loosing sync and causing the ECU to reset which would cut fuel and spark.
    Alex Weissinger
    ECU Systems Engineer
    Apex Speed Technology

  8. #8
    If the service manual lists them as CDI unit's, I'd believe that over what some guy on the internet here is saying.

    There is very little information that I could find on them. After lots of research, I could find one post on an internet forum that mentioned what they were. Additionally, considering the size and shape of a stock cbr ecu, I doubt there is enough size in there for the cdi module, let alone the heat.

    Alex's idea sounds plausible too. Also check sync position (motec thing sorry - relative position of sync signal to the ref). Make sure it's not moving around to much, which it can is things a little loose in the top end.
    Nothing is impossible. Improbable yes. But not impossible.

    Swinburne University of Technology

  9. #9
    Running the engine up at high rpm with the computer connected we've seen that the engine is losing sync.

    We've had to increase the number of teeth on our trigger wheel for the Bosch ECU, so it seems that we must be going outside the range of the sensor now it's seeing 50% more teeth.

    Has anyone ever had this problem before, and if so, do you have any suggestions for higher resolution sensors that will fit in the small space available?

    I'm going to ring round teams that I know are using the Bosch ECU with a Yamaha engine to see what they've done, and also give a few Superbike/Supersport teams a ring.

  10. #10
    It's losing sync, or the crank signal is dropping out / going erratic?

    Can you gap the sensor closer to the trigger wheel?

    Any noise or backfeeding in the signal lines will cause weird things too, is the signal leads ground shielded all the way to the ECU?

    Northwestern Formula Racing Alum
    Head Engineer, Frame/Suspension 2006-2009

    My '73 Saab 99 Road Race Build

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