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  1. #1
    Join Date
    Jun 2005
    Location
    Aberdeenshire
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    2,077

    Default 451 Smart Cdi 54 HP - A real Boneshaker

    Just had a 54 HP Smart in for repairs. DPF too sooted to regenerate and faulty temperature sensor, the one fitted in exhaust.

    Replaced temperature sensor and went for a drive to do a forced regeneration of DPF.

    What a bloody noisy car and boneshaker. My 450 Cdi is whisper quiet and comfortable like a Rolls Royce compared to the 451.

    Powerful engine though, more so than mine but not significantly more. Also, not cheap motoring like mine. Temperature sensor alone was 70 from Mercedes.

  2. #2
    Join Date
    Sep 2016
    Location
    Burnley
    Posts
    610

    Default Re: 451 Smart Cdi 54 HP - A real Boneshaker

    I could agree with that. They are not as good a car as the 450 by a long way. I have never driven a 450 diesel though but I hope it is the wheels which is why I intend to stick some narrow ones on mine when I get a round tuit.

  3. #3
    Join Date
    Jun 2005
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    Default Re: 451 Smart Cdi 54 HP - A real Boneshaker

    Pronounced turbo whistle too, tractor like idle and annoying road noise. This 451 has standard tyres and standard suspension. Perhaps the road noise is tyre related. In my 450 Cdi there is no road noise but then I roll on the cheapest tyres money can buy - Rotalla Setula. Paid only 28 each for the rear ones 175/55R15 shipping included.

  4. #4
    Join Date
    Sep 2016
    Location
    Burnley
    Posts
    610

    Default Re: 451 Smart Cdi 54 HP - A real Boneshaker

    Idle on mine is good, not really discernible as a diesel and in truth I like to hear the turbo spool up and down.

  5. #5
    Join Date
    Jul 2005
    Location
    over here
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    13,804

    Default Re: 451 Smart Cdi 54 HP - A real Boneshaker

    When I bought my 45/451 brand new in 2009 , I happened to look over the shiny new engine compartment..... and I just loved the mechanism noises of the brand new engine.
    It was like slick clockwork...
    fq101.co.uk

  6. #6
    Join Date
    Jun 2005
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    Aberdeenshire
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    Default Re: 451 Smart Cdi 54 HP - A real Boneshaker

    Forgot to state this particular 451 Cdi had been to 2 local garages before finally arriving at the not for profit Banchory Smart Centre charity where I am owner, director and sole mechanic. Charged 2 pub pints total for the job plus parts at cost.

  7. #7
    Join Date
    Jun 2005
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    Aberdeenshire
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    Default Re: 451 Smart Cdi 54 HP - A real Boneshaker

    Just received another 54 hp 451 Cdi for repairs. Check engine light on and engine on reduced power. Diagnostics reported no signal from DPF differential pressure sensor.
    What a pig to work on the 451. Sensor is bolted to left side of rear steel bumper hence rear panels must be removed for access.
    This is the worst car design ever for maintenance. Both side skirts has to come off plus rear hatch before rear body panels can be unclippped. Clips are brittle plastic and crack into bits. What on a 450 only takes 5 minutes turned into a two hour job.
    Never buy a Smart 451. Just a very poorly designed car and particularly unreliable.
    Last edited by tolsen123; 28th September 2018 at 08:15.

  8. #8

    Default Re: 451 Smart Cdi 54 HP - A real Boneshaker

    451s are fine, so long as you steer clear of the MHD and the diseasel. If you'd asked beforehand we could have told you that
    2004 Smart Fortwo Passion Cabrio, low miles, relegated to summer fun.
    2019 Fortwo Prime SE 900 - Dacia powered commuting scoot.
    2019 Volvo XC90 T8, 400bhp hybrid insanity family wagon.
    1991 Yamaha FZR600 3HE7 Kocinski edition, owned since new.

  9. #9
    Join Date
    Sep 2016
    Location
    Burnley
    Posts
    610

    Default Re: 451 Smart Cdi 54 HP - A real Boneshaker

    My car has two differential pressure sensors, one where Merc want it that is not connected and one that is bolted to the engine cover lip.

    Be interesting to see if you fix it. Mine still goes into safe mode under a very specific set of circumstances. I think Emily's Dad's ( or another member) does the same.

    Top gear motorway uphill and slightly too much throttle for the speed at between 3500 and 3800 for an extended period (>30 seconds) and it will always go into safe mode.
    Last edited by Mjolinor; 28th September 2018 at 07:35.

  10. #10
    Join Date
    Jun 2005
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    Aberdeenshire
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    Default Re: 451 Smart Cdi 54 HP - A real Boneshaker

    I removed DPF differential pressure sensor last night to bench test it.
    Still no signal. Then connected my China pressure vacuum pump to sensor's downstream DPF sensing port, applied a 0.4 bar vacuum and presto sensor sprang back to life.

    Got no idea as to why that worked and do not know how these sensors are constructed.
    Continued testing sensor with pressure applied to upstream DPF sensing port. Concluded volt signal and pressure now were withing spec.

    Won't be fitting this sensor back in the car as not mine. A new sensor should arrive just after lunch today from Mercedes together with a bag of assorted plasting fittings so I can get this useless Smart back together.

    To connect leads to sensor for bench testing I used short length of earth sleeve, the green yellow sleeves used in mains wiring to mark earth leads and short leads of test cable. The earth sleaves allow connecting test leads to the wee spade terminals on sensors and actuators without risking shorting out test cables. For larger terminals I use small insulated alligator clips.
    Last edited by tolsen123; 28th September 2018 at 08:59.

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