caddy 1.9tdi overboosting problem please help! ha ha.

Discussion in 'General Diesel Discussion' started by mattez69, Apr 10, 2012.

  1. mattez69

    mattez69 New Member

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    Caddy 1.9Tdi '02 ALH
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    Right then, i have a caddy '02 1.9tdi ALH. I have had a few intermittant turbo problems, one minuite over boosting, the next it under boosting. Stripped the VNT and its nw mint and totally free and functioning perfectly.
    However i am getting too much vac to the actuator, hence it is sticking in the high boost permanantly. i have,

    Checked the correct routing of the vac pipes (all now new and checked again after)
    swapped the N75 with the EGR solenoid, no difference
    stripped turbo and is as free as anything
    Checked that the actuator holds vacuum, it does

    is it possible that the vacuum check valve could be the problem?

    i have got full registered version of VCDS at my disposal, so just need to know how to use it!

    Starting to wind me up now to be honest, and when i get wound up i can't think straight.

    Cheers guys.
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  2. chittychittybangbang

    chittychittybangbang Administrator

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    2006 Jetta TDI
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    yes, check valve could be bad

    I'm 90% sure, VCDS cannot see vac line pressure since it's a purely mechanical thing and I don't remember seeing any sensors on it. You can view EGR and N75 solenoid duty cycle though. Just to take a look, engine measuring blocks -> look for duty cycle boost or MAP, forget what exact name is.
  3. mattez69

    mattez69 New Member

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    Caddy 1.9Tdi '02 ALH
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    zilch
    yea i did have a look on the duty cycle etc, i know it gives you peramiters but still not 100% sure what im looking at.

    Could that valve make it overboost? If i unplug the n75 electrical connector, it stops putting vacuum to the turbo actuator (on tickover) so is the n75 valve getting a false signal maybe? if so how? i didnt think that it should open on tickover or am i wrong? what sort or readings should i see on tickover?
  4. chittychittybangbang

    chittychittybangbang Administrator

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    I'm not sure what tickover means :dunno Hold the mouse over the measuring block and it should give a tip w/specs.

    Purpose of n75 is to control vac going to VNT actuator. No work = slow response or over/underboost.
  5. Seatman

    Seatman Active Member

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    Tickover is idle chitty, he means when the car's idling.

    Although the actuator holds vacuum I've read a number of times about the spring inside going weak and causing boost problems too. It's another possibility anyway.
  6. mattez69

    mattez69 New Member

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    Caddy 1.9Tdi '02 ALH
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    zilch
    sorry chitty, i meant idle! just confused as to when the n75 should be allowing vacuum to the actuator? is there a way to do this through vag com? Also do you know what auctually tells the ecu to engage and disengage the n75? plus i did swap the EGR solenoid with the N75 and it was the same?
    i have ordered the vacuum check valve will be here friday, was only 10 plus vat, so worth a laugh. Driving around atm with the n75 valve unplugged and no boost.

    I have checked the spring in the actuator, when i checked for the diaphragm holding vacuum. did cross my mind, so in that case im getting too much vac, and the N75 is alright, so failing the check valve, what else could it be? im completely stumped, and completely pissed off. Think i need to be looking at how the N75 is controlled if the check valve doesnt work.

    Could check the amount of vac at idle if i knew what it was supposed to be?
  7. mattez69

    mattez69 New Member

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    Caddy 1.9Tdi '02 ALH
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    the n75 holds and prevents vacuum getting to the actuator, until the electrical connector is connected then it holds the vacuum and overboosts hence why im trying to get to the bottom of what makes the N75 work pre-ecu.

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