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    Audi A4 2.5 V6 TDi (engine code BFC) Archived Message

    Posted by Dave Hill on July 11, 2007, 4:58 pm

    I have the same Audi in that I recently replaced the needle lift sensor on. It is a 2003 Audi A4 2.5 V6 TDi (engine code BFC). It has repeatedly logged the code 00575 intake manifold pressure (sporadic: resulting limit not reached). Upon start-up the turbo actuator arm can be seen to travel lazily about half way between open & closed positions.

    The vacuum is in excess of 30” at the take off point near the servo hose.

    I have scoped the MAP sensor on the top of the nearside intercooler & it appears to be ok. Although its hard to be sure of a good reading on a stationary vehicle. Also when engine speed is approximately 2,000 rpm & I introduce a simulated voltage into the MAP output wire I can see the N75 valve duty alter in response. Also the actuator arm moves as expected (I think anyway).

    I have activated the variable vane actuator via the Launch (basic settings group 011) this cycles the actuator on & off & the N75 valve duty cycle confirms this. Observing the control diaphragm it can be seen to initially open fully but then it is seen to slowly close, even though the duty cycle is showing fully on. I have clamped off various sections of vac hose whilst observing the vac (on the mitty), in the hope that I could see were the vacuum is being lost, but nothing shows up as wrong.

    I was wondering if it might be a dodgy N75 control valve? When these fail, do they normally just fail to operate or do they lose efficiency?

    Any tips or advice gratefully received.

    Thanks for reading

    Dave (Hill)

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