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Anyone fitted a boost guage to a 2.5 V6 Tdi ?

Discussion in 'Diesel forum' started by Magnet, Apr 2, 2010.

  1. Magnet
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    Magnet New Member

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    [Apr 2, 2010]
    Hi,

    I was wondering if anyone had fitted a boost gauge to the 2.5 tdi v6, and if so where you tapped-in to measure the boost...

    I.e. intercooler pipework or somewhere else?

    I'm looking into fitting a gauge as every now and then I get a hesitation with the car after it's been driven under load... (It happens randomly /occasionally in 2nd, 3rd, 4th at high revs and when I change to the next gear up I get 'Judder judder / hesitation) I think it could be the boost / turbo or load related - sticking VNT or N75 , but I'm not 100% sure, and I'm hoping the gauge will confirm this by showing details of pressure when operating normally and when the hesitation occurs.

    Any thought or experience on this please post.

    Thanks Rob
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  3. fjtwelve
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    fjtwelve Moderator Staff Member Moderator

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    [Apr 3, 2010]
    What has led you to suspect boost pressure? If the N75 is n the way out i don't think you get judder, more a general and softer loss of power. Having just suffered a failed VNT mechanism i got an overall loss of power and plenty of black smoke as the engine didn't get the air to match the fuel injected. I would be more inclined to suspect fuel supply. Anymore details on car or symptoms?
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  4. Magnet
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    Magnet New Member

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    [Apr 4, 2010]
    Hi,

    Thanks for the reply fjtwelve,

    The car is a 2001 2.5 v6 quattro (avant). It seems to run fine 99% of the time, just on occasion when driven hard, high revs and held at high revs before changing to the next gear say from 2nd to 3rd off a roundabout the judder / hesitation will happen and black smoke then appears.

    I'm getting really poor MPG (I think) anywhere from 23 - 26 mpg on 15 - 20 min trips to work, which is mainly A road at 60 - 70 mph. On longer (100 mile) journeys I get 30 - 35 at a 70 mph ish. If driven hard I get around 20 - 23 mpg. These fig.s are all based on the on board comp readings.... around 400 - 430 to a full tank.

    Water temp sits around 80 most of the time, and goes to 90 when driven hard.

    I disconnected my MAF which made no difference to the cars performance so it's probably duff and isn't helping things. I've recently replaced the injector which has the timing sensor on it which has massively improved the car as the judder was happening pretty much every day... Maybe I should get the other injectors tested / calibrated.

    I managed to find a take-off point for the boost gauge.... Just after the intercooler the alloy manifold has a 13 mm bolt which is just after the butterfly valve (throttle control?), just need to find a barbed fitting which will fit.

    Could you tell me what sort of MPG you get from yours?

    Many thanks

    Rob
    Last edited: Apr 4, 2010
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  5. fjtwelve
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    fjtwelve Moderator Staff Member Moderator

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    [Apr 5, 2010]
    Your mpg sounds OK to me for the motorway cruise, otherwise a bit low.
    Your thermostat sounds shot, water should be a solid 88-90C, oil temp around 80 unless driving hard or hot conditions.
    Averaged 33mpg driven enthusiastically in Scotland for 2-3 years, now down to around 30 in Cornish lanes, and below since i started all these changes.
    Have you had a VAGCOM check done and all the faults cleared?
    I wonder if your injection pump timing needs checking if the needle sensor made so much difference, or if the pump needs servicing/rebuilding. How many miles has the car done? Could also need the fuel filter changing.
    If the boost was off all the time then i would suspect a leak, but if its coming and going then maybe the N75 is dodgy as you suspect, or the VNT mechanism is sticking. I have read of both, one case the diaphragm of the N75 had split, difficult to spot.
    I have tried disconnecting the MAF on mine and replacing it when there was no difference, but the problem wasn't the MAF so its not a bullet proof test as i once thought it was.
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  6. Magnet
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    Magnet New Member

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    [Apr 5, 2010]
    Hi, the clock shows 120k miles and the history tie's up. I had the codes pulled a month or two ago which identified the needle lift sensor, but nothing else. When i got the car last year i did the fuel filter. Oil and water and panel filters. since i've had the car i think, (but cant be sure, as after a while you do get used to things) that the power has gone down. I struggled to keep up with a golf today, a 2.0 tdi think it was a 140. Hopefully once this gauge is connected i'll know if it is the boost... By the way do you know what the max boost should be ?
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  7. fjtwelve
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    fjtwelve Moderator Staff Member Moderator

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    [Apr 8, 2010]
    Lift the rocker covers and see if a rocker has popped out
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  8. tekno_al
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    tekno_al New Member

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    [Nov 3, 2010]
    a bit late I know, but did you ever completely solve the juddering problem?
    I have exactly the same problem.. it's going into the local indie garage to see if they can sort it (still under warranty), but interested to know what the root cause is.

    Alan
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