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    Gen 1 Hayabusa, no top end under load
    #1
    Senior Member
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    Jan 2015
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    Norco, CA
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    well, just like it says, when driving the car I can only use about 1/8 to 1/4 throttle, it acts a bit like it hits a rev limiter at about 6500 RPM, in neutral revs out and sounds fine, not so much duning
    I was kinda hoping it was fuel pressure, it seems right in neutral, 43 psi, I don't have a way of checking under load. I have my exhaust off and at the shop getting an O2 bung installed so at least I should be able to tell something.
    Car ran good last year, took it to Pismo in July, I had a battery issue, something strange part of the battery was melted but not in the area closest to the exhaust? 4 wheel parts warrantied it, thank you very much! I got a new battery, mover it to the cool side of the fire wall, added a battery cutout switch and good feed through for the power, that was about the only thing changed, I checked and cleaned the air filters, they were clean, changed the spark plugs, they looked great and did not get any better, now the only change made was to add a pressure gauge on the fuel line and I changed the fuel filter. there is an outside chance it is the fuel filter but if memory serves me it was pretty new so I doubt that would be it, but it does seem like it is running out of fuel.
    No codes showing up, could something be putting it in limp mode and still not through a code? I'm thinking I need to start checking sensors.
    Any busa experts in the house.
    I have an auto meter oil pressure gauge, anyone tried using it for a fuel pressure gauge?
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    Re: Gen 1 Hayabusa, no top end under load
    #2
    Millenium Member plkracer's Avatar
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    Aug 2006
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    Monroe Wa
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    3,498
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    There isn't limp mode without a code. Even without some sensors, it will tend to run rich.

    I have had ngk plugs crack the porcelain on a couple occasions. It acts like what you mentioned, and it sounds muffled, like the exhaust is choked. I was able to nurse mine up in rpm, then it would fall flat when it was punched.

    Edit, just noticed you said you changed the plugs, not just cleaned them.

    If it has sat for a while, could be a sticking or partially plugged injector. Hard to tell fuel or ignition on these motors. Afr will definitely help, and should weed out most fuel delivery problems, but those can be caused by a bad signal to the ecm by the tps or map sensor.
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    Re: Gen 1 Hayabusa, no top end under load
    #3
    Millenium Member Deranged's Avatar
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    Allendale MI
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    This sounds like the EXACT same issue I had with my GSXR 750. It had nothing at mid to top end, just fell on it's face. I could cruise around and still dune just fine, but when I wanted to really have fun it said nope.
    I went through all the same things you did. I actually pulled my injectors out and did the actual cleaning process with compressed air and cycled the injector o see the spray pattern. It was fine.
    Here is how I did that.
    I took a piece of 3/8" fuel line about 10" long and used a hose clamp to clamp it to the injector. Then I filled the hose with cleaner. Next I adjusted my air regulator to 40 PSI and stuck it on the hose and hit it with constant 40 PSI. After that I used a 12v battery with some clips and just tapped the leads to the injector to pulse the injector. Worked great.

    Now onto my issue. No codes, TPS was reading fine and i had 43 PSI. I literally took my entire fuel pump apart. Took the sock off, the pump itself off, everything. even the fuel bypass valve. This will dump fuel back into the tank under little demand. Take that guy and clean the crap out of it and cycle it with compressed air. Clean the inside and outside of that pick up sock. Now onto where my issue was. That big black plastic thing that the pump fits into, as well as the fuel pressure regulator...yeah, there is a non serviceable filter in there. I soaked it with carb cleaner, shook it, sprayed it and I was SHOCKED as to how much junk was in there!! I sprayed out every opening over and over, filled it, blew it until the cleaner was clear coming out of it. I let it sit over night and re assembled in the morning. It was 100% alive again and better than ever. Our pumps are very similar in design, assuming you have the stock pump. Give this a shot.

    Hope this helps.

    Justin
    Nowhere near the desert.
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    Re: Gen 1 Hayabusa, no top end under load
    #4
    Senior Member
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    Jan 2015
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    Norco, CA
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    I will look into the sensors to make sure they are doing what they are supposed to do, on the suzukihayabusa site it was also suggested to start the engine and unplug the cam position sensor, I was told that that is used for starting and not much else but if funky it could effect the map. I'll clean the fuel pump this weekend, that has been my suspicion from the start that with no load it has plenty of flow, under load where it needs more flow the pressure could be dropping de-fueling the engine.

    So Justin,
    do you think if you had just cleaned the pump, you would have been good?
    Also the pump that is in the car is from the original engine GSXR750, I assume that is where the pump came from, I wondered when I put the busa engine in if it would supply enough, it did before this latest issue.
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