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al-jam01
Guest
Ok maybe Ive got the numbers wrong! It's the one to stop the dump valve working when it shouldn't!
N75 is boost control valve not safety valve? The N249 valve is the safety valve... If you rip out N75 wastegate will be left open so will be safer for turbo as it won't build much boost..
al-jam01
Guest
In short - you can't bypass the N75. You can bypass the N249 but don't bother - I did and it made no difference apart from a strange noise on dump so I undid it.
This belief on the forums that "the DV dumps when it shouldn't" is a myth - the ECU will use the N249 to open the dump valve when it doesn't need to run the turbo so hard to meet the requested torque. You'd only have a problem if you found the DV was dumping at wide-open throttle. If not, leave it alone. It's a safety device for the turbo, you wouldn't remove seat belts would you? Or bypass the radiator?
This belief on the forums that "the DV dumps when it shouldn't" is a myth - the ECU will use the N249 to open the dump valve when it doesn't need to run the turbo so hard to meet the requested torque. You'd only have a problem if you found the DV was dumping at wide-open throttle. If not, leave it alone. It's a safety device for the turbo, you wouldn't remove seat belts would you? Or bypass the radiator?
N75 is the boost control valve which operates the wastegate on your turbo - Wastegate open means some exhaust gasses are allowed to bypass the turbo rather than spooling it. This ends up in you only being able to acheive a few psi of boost. (You can see the effects of this by unplugging the N75 - it's at the top of your turbo intake pipe).
N249 is the valve which operates the DV and is used by the ECU when foot is taken off the throttle to release boost as quick as possible to avoid backpressure through turbo. It is also used as part of the traction control system and will open the DV if a lot of wheelspin is detected to rein in the power and re-gain traction.
N249 is used for reducing boost
N75 is used for increasing boost
N249 is the valve which operates the DV and is used by the ECU when foot is taken off the throttle to release boost as quick as possible to avoid backpressure through turbo. It is also used as part of the traction control system and will open the DV if a lot of wheelspin is detected to rein in the power and re-gain traction.
N249 is used for reducing boost
N75 is used for increasing boost
Depends on how you bypassed it. If you took the charge pipe to N75 feed and attached it to the N75 to wastegate pipe, the wastegate would be permanently shut. If you connected it to the N75 to TIP then the wastegate would be permanently open. Neither of the above are advisable.
al-jam01
Guest
Ok so I'm getting the dump valve opening under acceleration, what's the best way to sort this, the only fault code I've got is for the intake air temp sensor fault of which I have one on order!
al-jam01
Guest
al-jam01
Guest
It doesn't do it all the time! No leaks on any pipe work, have just had it all off as changed a piston and had crank reground, as well as many other parts!
What Pat said.
It will either be a leaky/split diaphragm (more likely), or possibly a faulty N249.
Bypass or new DV to eliminate one or the other, obviously bypass is cheaper option to go with first.
It will either be a leaky/split diaphragm (more likely), or possibly a faulty N249.
Bypass or new DV to eliminate one or the other, obviously bypass is cheaper option to go with first.
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