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  1. #1
    Join Date
    Mar 2014
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    Somewhere on the Wirral
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    968

    Default 450 CDI not boosting

    My 450 CDI has had a replacement turbo, EGR valve and a new exhaust fitted but it is not making any boost whatsoever and I can't figure out why this might be. The actuator seems a bit stiff but apart from that, the car does appear to be running normally but severely lacking in power, meaning ~55mph at best. I don't recall the engine light being on when this was happening this last time I drove the car.

    My question is: Why would it not boost? As far as I can think of at the moment, there is the following to look at:
    • EGR valve blocked up
    • Boost hoses not tightened up
    • Grease up the wastegate actuator/replace if required?
    • Splits in the pipework
    • Pipework blocked up(?)
    Has anyone had this before? Is there anything else to check on this engine as to what it might be?

  2. #2
    Join Date
    Jun 2005
    Location
    Aberdeenshire
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    2,100

    Default Re: 450 CDI not boosting

    Please add to your list:

    1) No preload on waste gate causing reduced exhaust pressure insufficient to drive turbo.
    2) Severely holed intercooler.
    3) Engine gone into safe mode but then there should be a check engine light. Perhaps blown bulb?

    Cracked waste gate aturator control hose is common but that leads to overboost, check engine light and reduced power.

  3. #3
    Join Date
    Mar 2014
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    Somewhere on the Wirral
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    Default Re: 450 CDI not boosting

    Many thanks tolsen. Will look into those, especially the intercooler as that is the original one from 2001.

  4. #4
    Join Date
    Sep 2016
    Location
    Burnley
    Posts
    653

    Default Re: 450 CDI not boosting

    Seized pressure release arm pivot in the manifold. I do not know if the 450 suffers from that problem but for sure the 451 does.

    Lubricate it with graphite only, the sort of stuff you buy for keys and locks.

  5. #5
    Join Date
    Feb 2006
    Location
    Hampshire
    Posts
    1,113

    Default Re: 450 CDI not boosting

    Not overly familiar with the CDI engine but I understand it's largely based on similar architecture to the 600/700 suprex?


    If so, does it use a cycle valve to control the turbo wastegate as many of the petrol versions do? As these can be a common failure. If it is this, the usual way to find out is to reboot the ECU (battery off & then back on again, or pull out then reinsert the ECU fuse).


    This then restores power for a short time before the fault shows up again.

  6. #6
    Join Date
    Mar 2014
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    Default Re: 450 CDI not boosting

    To close this one out, it looked to be a knackered temperature sensor in the intercooler which wasn't reading and I suspect was loose, losing pressure as a result. Had that replaced and now it is running properly.


    If so, does it use a cycle valve to control the turbo wastegate as many of the petrol versions do? As these can be a common failure. If it is this, the usual way to find out is to reboot the ECU (battery off & then back on again, or pull out then reinsert the ECU fuse).

    I don't believe the CDI has a cycle valve like the Suprex engines does from what I can remember.

  7. #7
    Join Date
    Jun 2005
    Location
    Aberdeenshire
    Posts
    2,100

    Default Re: 450 CDI not boosting

    So temperature sensor had been vandalised by an unskilled mechanic or owner.

    I have seen that before as that happened to mine when being serviced by Aberdeen King Street Mercedes. They broke both cable and sensor housing.

    To remove sensor one must first disconnect connector as the connector locks sensor release levers in place.

  8. #8
    Join Date
    Mar 2014
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    968

    Default Re: 450 CDI not boosting

    Duly noted, thanks.

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