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A4 Tdi AFN starting issues...

Discussion in 'Diesel forum' started by Final 3Green Land, Apr 30, 2011.

  1. Final 3Green Land
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    Final 3Green Land Member

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    [Apr 30, 2011]
    Hi... I wonder if I can pick the brains of the experts here as I am a little lost as to the cause of my problem....


    Three days ago, I was driving my TDi along the road when the auxiliary drive belt failed, possibly due to the Air Con Tensioner allowing movement of the a/c belt which failed then shredded the main drive belt... (alternator, water pump etc...)

    The engine continued to run albeit with vastly reduced power. Got to the hard shoulder with the engine still running but with the alternator charge light illuminated, as expected... Went to move forward a little to get off the road but the engine stalled and would not re start.

    Had a look under the bonnet and could see that the shredded belt, (now wrapped around the crankshaft pulley) has torn out some wiring from the front of the car, the green and yellow A/C wire and a four wire loom which runs from somewhere near the Mass flow meter across the front of the engine bay and enters a large red round connector plug, located next to the power steering fluid reservoir. It had also detached one of the vacuum hoses, connected to a small valve, located above the air con compressor, (this valve? looks like a window washer pump but has three air outlet/inlet pipes, made by piershrader? and a two wire connector block with 12v and 6v on these wires/terminals respectively. Have been told this might be a N75 valve what ever one of those is) the pipes route up to another valve along side the turbo unit and up to the air-box I seem to remember....


    All the wires were replaced in the correct combination, ie brown/white to brown/white etc, the green and yellow wire replaced and the disconnected pipe reconnected, inspected all fuses I could find, in the fuse box on the right dash end and under the bonnet also on the drivers side and they are all fine. A new alternator drive belt was fitted, battery charged (due to the vehicle being recovered to home with the hazards going)....


    Turned engine over, which it does freely but fails to fire up.


    Does any one know a likely cause or where I should start looking. I do not have access to a code reader.

    Any suggestions would be appreciated.
    Last edited: Apr 30, 2011
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  3. adamss24
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    adamss24 Well-Known Member

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    [May 1, 2011]
    Take the rocker cover off and look for smashed followers, i none found (pay close attention to spidering on the flat side of the lifters as it means the valves hit the pistons (wich i am shure they did !) as the engine timing jumped. It will need resetting the timing (cam at TDC,pump in the locked factory position and crank at tdc) then pray it starts and no valves are bent. I bought a few cars with bent valves due to the aux. belt tensioner failling and the belt jumps then wraps round the crank thus the cambelt jumps a tooth or two. If the engine starts and runs then it might do that for a good few thousands miles after wich it drops a valve (ussualy the no.2 piston wich will destroy the engine:scuffed piston bore and cracked pistons + damage the head beyond repair) dont know why but i had a few engines with this failure. I would get a good 2nd head and fit that or rebuild the existing one you have at the moment with new lifters, seals and valves... If you're interested to sell the car as it is, i might be interested...
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  4. Final 3Green Land
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    Final 3Green Land Member

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    [May 1, 2011]
    I think we have crossed wires here... (not the rewiring)

    It wasn't the cam belt that failed. It was the auxiliary drive belt. And the engine was running nicely after the belt came adrift.

    And Not a snowballs chance in hell of selling the car. If I wanted to sell the car I would have listed it in the for sale section.


    Any sensible offers of faults please.
    Last edited: May 1, 2011
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  5. Final 3Green Land
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    Final 3Green Land Member

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    [Sep 1, 2011]
    Well I thought I would post what was wrong with the old girl...

    When the belt failed it, tore some of the wiring loom from under the bonnet, this went under the cam belt cover, wraped itself around the crankshaft pulley and caused the timing belt to jump three teeth!

    All going well now.


    So no cheap easy fix car for you Adamss 24!!
    Last edited: Sep 1, 2011
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  6. adamss24
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    adamss24 Well-Known Member

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    [Sep 1, 2011]
    I do hope you did not bend any valves mate, they will rub against the valve guide and drop in a few thousands miles... Also when the pistons hit the valves all that energy hits the follower and it breaks the top of the lifter (that's why i mentioned spidering on top of the lifters). I did rebuild a few dozens of them engines, last one dropped a valve due to running for a few thousands km with one tooth off on the belt. Result: bent rod, cracked piston, funked head and scored piston bore on cyl. 1 ! 3 teeth is a lot for the belt to jump and i would replace the lifters just as a precautionary measure. Also, the valves bend at the cotter end and what usually happens is they tend to shear due to extra stress as the valve spring puts pressure sideways ! I have loads of bent rods in the shed just can't be arsed to look for then right now ! Here's what you should look for:
    [​IMG]
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