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Thread: Overboost??

  1. 10th September 2011, 02:25 PM #1
    ecn226
    ecn226 is offline Fossicker
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    Overboost??

    I picked up my 2002 auto TD5 disco three weeks ago and so far I am happy with it except for a surging problem under hard acceleration. This was happening at about 3500 rpm on a flat road. I haven't had it on any hills yet so I don't know what it would do there.

    Anyway after doing a few searches I thought that it may have been the boost modulator, so this morning I bypassed it. Problem is still there but has moved up the rev range to 4200 rpm. So I am now thinking maybe a combination of boost modulator and MAF? Is there any way of determining if it is the maf other than using a scan tool which for me would mean a trip to a dealer or other mechanical workshop. Anyone have an other ideas at all?

    Thanks
    Peter
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  2. 10th September 2011, 04:09 PM #2
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    Fluids
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    Sounds like overboosting ... someone has wound the turbo wastegate up too far to increase the boost ... it will cut fuel at over 21psi boost ... find a nearby AULRO member who has a Nanocom, and check to see what the boost is running at ... otherwise, wind the turbo wastegate back in say 1/2 turn increments until it doesn't happen anymore.

    Everything you should need can be found in the "Good Oil" forum area.
    Kev..

    Going ... going ... almost gone ... GONE !! ... 2004 D2a Td5 Auto "Classic Country" Vienna Green

    2014 MUX LST with fruit
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  3. 11th September 2011, 11:52 AM #3
    cozab
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    Obviously there is a problem but You really shouldnt need to drive it anywhere near 4200rpm especially on the road, being a diesel it most likely wont be making any power there anyway..
    Just something to consider..
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  4. 11th September 2011, 12:38 PM #4
    ecn226
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    I agree 100% cozab. Ordinarily I would be lucky to go over 3000rpm but I was just seeing if bypassing the boost modulator had fixed the surging.

    Thanks Fluids. Are you thinking boost modulator and someone has wound up the boost to far as well?
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  5. 11th September 2011, 02:21 PM #5
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    Fluids
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    The modulator wastes boost ... to prevent overboost ... by opening the wastegate ... so yes, it may be faulty.

    You need to get a Nanocom or similar on it to see how much boost it's making first.
    Kev..

    Going ... going ... almost gone ... GONE !! ... 2004 D2a Td5 Auto "Classic Country" Vienna Green

    2014 MUX LST with fruit
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  6. 19th September 2011, 02:30 PM #6
    ecn226
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    Thought I would post back and let everyone know just how far off the mark I was, thinking that the problem was over boost. I was going to book it in to be sorted out this week as I am on holidays at the moment but yesterday I replaced the air and fuel filters and problem solved. So I am a happy disco owner now. Just goes to show that we probably should look at the simple things first.

    Peter
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