Stranges noise at 3.5k
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From: England
Stranges noise at 3.5k
Sounds something like a Stuka or the noise a jet makes when it spins up the turbines. Always at exactly 3.5k, always under load, doesn’t matter what gear or how much throttle. If you hold revs it’ll make the noise constantly.
It doesn’t do it off throttle letting the revs drop and it won’t if you just rev it in neutral. Sounds like it’s coming from the back so Stu thought it might be the fuel pump graunching, I had some crazy AFRs too. Changed the pump, AFRs now stable, noise still there.
Anyone heard this before?
It doesn’t do it off throttle letting the revs drop and it won’t if you just rev it in neutral. Sounds like it’s coming from the back so Stu thought it might be the fuel pump graunching, I had some crazy AFRs too. Changed the pump, AFRs now stable, noise still there.
Anyone heard this before?
Last edited by jack_am; Aug 25, 2018 at 01:20 PM.
Jack,
If you suspect it is turbo related then you could wire up an external mic and place it near your turbocharger. You will certainly hear all sorts of interesting turbo sounds! What type of exhaust are you using? Do you also have a cat? The "Stuka" sound may be the result of harmonics resonating from the exhaust system.
If you suspect it is turbo related then you could wire up an external mic and place it near your turbocharger. You will certainly hear all sorts of interesting turbo sounds! What type of exhaust are you using? Do you also have a cat? The "Stuka" sound may be the result of harmonics resonating from the exhaust system.
I have the same issue and just came to the forum to find a thread. How serendipitous... I think its a harmonic vibration.
I just got done fixing a 100% broken vacuum tube boost leak, and the car is pulling like a bat out of hell and much quieter, which is why I think I hear the noise now.
I just got done fixing a 100% broken vacuum tube boost leak, and the car is pulling like a bat out of hell and much quieter, which is why I think I hear the noise now.
Last edited by j a r o d; Aug 29, 2018 at 10:20 PM.
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From: England
Yeah, it's an odd one in that it happens at a very precise, very narrow RPM range.
I need to re-build my downpipe to give a bit more ground clearance, so I'll soon find out if it's a resonance thing by making the exhaust shorter. If not then I guess it'll be a heatshield or something, convinced it can't be anything in the engine bay as I'm sure it would have exploded by now if there were metal on metal grinding at 3.5k rpm.
I need to re-build my downpipe to give a bit more ground clearance, so I'll soon find out if it's a resonance thing by making the exhaust shorter. If not then I guess it'll be a heatshield or something, convinced it can't be anything in the engine bay as I'm sure it would have exploded by now if there were metal on metal grinding at 3.5k rpm.
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