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    Hayabusa Clutch Switch Secrets
    #1
    Millenium Member plkracer's Avatar
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    I'll start off by saying I was tearing my hair out for the better half of a week trying to pin this one down. If you don't want to read my experience, feel free to scroll down the the explanation below. This most likely applies to all the modern GSXR engines.

    The Hayabusa (along with most of the GSXR line) uses gear specific fuel and timing maps to better control the power from the engine. Most people know the ignition timing is less advanced in the lower gears, so many people fit a TRE (timing retard eliminator) to trick the ECU into thinking the bike is in 5th gear. The fifth gear map is the most radical, with the most advance down low, and the 10,800 rpm rev limit.

    The unfortunate part is that not many know there is also a neutral/clutch-in map to make the bike idle more smoothly when stopped. This map is only 2 dimensional, applying an equal ignition timing to all throttle positions, and a generally richer, far less optimized fuel mixture.

    What is even more unfortunate is that many people are running the neutral map without a clue! Apparently, the harness in my car was reworked by King Sand Cars. (I'll get into the specifics in a bit, the clutch wire was permanently grounded) If this is true, then "all" of their Gen 1 cars would be running in the neutral map, and stories of the huge gains from the TRE are completely false.

    So onto my story,

    I bought a mostly complete 2 seat Hayabusa (Gen 1) rail at the end of last summer, and took it out for a weekend to get a feel for what it needed to be tuned in and completed. Like most kit car engines, the wire harness was a mess. There were fuses all along the loom, mismatched wires, suspect connections, and no documentation to go with it.

    I started the rebuild of the car by completely removing the harness, tearing it all down, and rebuilding it from the ground up with the intentions to have all the relays, fuses, and terminal blocks in the dash. The harness already had a TRE hard wired in (of course) so I tore that out, and replaced the stock wiring, and the clutch switch wire (the black wire with a yellow trace) was permanently grounded. I knew this was a no-no from my previous build, so I broke that wire off, and carried it to the dash. I didn't specifically check the car during the first trip to make sure the gear specific maps were working correctly, but I doubt they were since the wire was grounded.

    In the dash, I used a relay, with the hot coming from the start pin of my ignition, and a ground wire directly from the terminal block. The black/yellow wire was connected to the normally open contact. This would close the relay only when the key is turned to start, therefore only providing ground to the clutch wire during a start, correct? Yes, correct. I thought I had the problem licked, since I only needed to turn the key to get the engine to start.

    After completing the rest of the wiring, and a few odds and ends, I took the car back out. It seemed to run well, and I even managed to hit the rev limiter in third while cresting a roller.

    I installed a speedhut tachometer during the rebuild, so I recalled my peak rpm when I got back to camp. 10,500 right on the money. That's odd, these engines redline at 10,800 (Gen 1). But the neutral map has a rev limiter at 10,500! So after all that, I was still running the neutral map.

    Back to the drawing board. I checked my wiring to and from the gear position sensor, ecu, clutch switch, etc. I checked gear specific resistance and voltage to the ecu. I spent hours searching for a solution all over the web. Then, I came across an interesting post regarding the Gen 2 ECU's.

    Apparently, the ecu puts out a small voltage on the positive starter wire. This voltage is used to monitor the condition of the clutch switch through a "back door". When the user starts the bike, the switch applies full power to the line, causing the relay to close. For this to happen, the clutch switch must be grounded. But if we keep it grounded, this small voltage from the ECU is also drowned out, causing the ecu to fault to the neutral map.

    I somewhat disregarded this theory due to the fact that I have a Gen 1, and the relay I used has such high resistance, it shouldn't be grounding out that voltage from the ECU, but I was dead wrong. (Causing me to waste a couple more hours.)

    Even that large resistance was enough to drain the ~2.5 volts from the ecu. I first noticed it when I was in first or second gear, and I would hit the starter while the engine was running. I had the clutch wire disconnected, so the starter motor would not activate. The RPMs would drop ~100 rpm, which was odd, since there was no load on the system. I then tried it in 5th gear, which caused the RPM's to rise! Therefore, it was indeed changing the map, but how?

    I was putting 12 volts to the starter wire, causing the ECU to read a high voltage on that line. Because the clutch wire was not grounded, the ECU reverted to a gear based map. Releasing the starter caused the ecu to jump back into the neutral map. I finally traced it down to that little relay. Disconnecting it completely, and using a switch to activate the clutch instead proved to work beautifully.

    ----------------------------------------------------------------

    Long story short, I don't know of a foolproof way to bypass the clutch switch. I'm going back to the foolproof method of having a separate switch to activate the clutch when I start the car. (Might tie it into the clutch line eventually)

    Here are some common bypasses, and why they don't work

    #1 grounding the clutch wire
    -This causes the ecu to see low on the clutch wire, keeping the ecu in the neutral map
    #2 Cutting the clutch wire near the ecu, then grounding the wire to the starter relay
    -While the clutch wire going to the ECU will not be held low, the start wire from the ECU will see low. Either pin will cause the ECU to revert to the neutral map.
    #3 Using a relay (like I did) to ground the clutch wire to start the car only.
    -Even large resistances have enough influence over the small ecu signal that it is actually held low, causing the ECU to run the neutral map.

    So all in all, there isn't a (known) good way to bypass this system. (Besides flashing your ECU)

    Possibly a transistor instead of a relay?
    The large input resistance may not drain the ECU's signal, but could it supply enough power for the relay?

    Could we cut the start wire from the ECU? Or is is needed to activate some sequence to start the engine?

    Anyways, just though I would share my finding with everyone. I know a lot of the Edge guys are doing option #2 above, and are actually robbing power from their engines. From what I found with my harness, I wouldn't be surprised if many of the harnesses being reworked by big names are also causing the ECU to run the neutral map. Who knows, maybe yours is the same? It'd be worth a look (and probably 5 HP!)

    Here is a link to the only thread I've found that mentions this "back door" approach.
    Last edited by plkracer; 06-18-2014 at 01:43 AM.
    Proud owner of a two seat pucker-mobile. Funco inspired mini buggy powered by a Busa. Giving out free rides to anyone brave enough.
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    Re: Hayabusa Clutch Switch Secrets
    #2
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    I use a seperate switch on my zx12. But a hydrolic switch on the clutch line (brake light switch) works too. I have read many post about all big liter bikes and clutch switch.

    Great write up!!
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    Re: Hayabusa Clutch Switch Secrets
    #3
    Senior Member JD66's Avatar
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    Very helpful info, thanks for posting. Until I read this, I would have been in the "neutral map" class.
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    Re: Hayabusa Clutch Switch Secrets
    #4
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    I did a fair amount of research on the GSXR 1000 for the XK1000 build, it requires a clutch switch for the very reasons you list above. It will limit the revs if the clutch is pulled in. I have a hydraulic setup with a pressure switch used to active and close the circuit (ground) when the pedal is pressed. That's the same way the stock ones are setup.
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    Re: Hayabusa Clutch Switch Secrets
    #5
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    This is some good information and needs to be made a sticky.Information like this is hard to find and will help many with their builds, Thank You !!
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    Re: Hayabusa Clutch Switch Secrets
    #6
    Keeper of the Asylum K-fab's Avatar
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    Good call on making it a sticky.
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    Re: Hayabusa Clutch Switch Secrets
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    Senior Member studio5o's Avatar
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    Great infoin this thread....while doing a search for my bypassing my tl1000s clutch switch ran into this bit of info and did it to my bike and seems to run just fine.....dont know much about electronics but hope it helps...
    Safe Clutch Switch bypass
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    Re: Hayabusa Clutch Switch Secrets
    #8
    Millenium Member Deranged's Avatar
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    That was quite a read! Great, well documented info, thanks!!

    Justin
    Nowhere near the desert.
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    Re: Hayabusa Clutch Switch Secrets
    #9
    Millenium Member plkracer's Avatar
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    Quote Originally Posted by studio5o View Post
    Great infoin this thread....while doing a search for my bypassing my tl1000s clutch switch ran into this bit of info and did it to my bike and seems to run just fine.....dont know much about electronics but hope it helps...
    Safe Clutch Switch bypass
    Which method did you use? Either one mentioned in the first post will not work properly, as I found out.

    Also, he mentions a starting fuel map, which does not exist. There is the neutral map, which is selected by either grounding the clutch wire or by grounding the solenoid, without a start signal.
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    Re: Hayabusa Clutch Switch Secrets
    #10
    Senior Member studio5o's Avatar
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    I used the #2 option utilizing the relay......perhaps there may be difference between the inline fours and the v- twins regarding fuel maps. Not an electrical guy just followed the directions in the thread and it worked out well for my motor.
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