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Common rail injector testing (leak off method)

Discussion in 'Engine, Drivetrain, Fuel and Exhaust' started by premmington, Feb 14, 2007.

  1. premmington

    premmington Senior Member

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    Common rail injector testing (leak off method) This is very simple. I hope you can follow the following text. Remove leak off pipes from injectors, connect soft transparent 1/8" or 3.2mm pipe of the same length from each injector leak off fitting & place other end in an identical 250ml (ish) transparent bottles. Start-run the engine for a few minutes, all bottles should have the same amount of diesel in them, after the test run at idling speed. Any bottle with more fuel in it, indicates a fault with the injector connected to the bottle in question. It is possible for the injector to have a fault and have less in the bottle, but normally a faulty injector will leak off more fuel due to a worn internal injector components. If it has less derv in it, the chances are the coil in the injector is not being activated due to, dodgy internal injector coil or the host wiring to it .
    My leak off test kit has six identical "tesco indian tonic water bottles" connected to a short length of wood by screws thru lid, from the inside. A small hole is bored on the neck of each bottle, to make a snug fit for the pipe to enter the bottle. The wood, has a length of welding wire connected to it, so that I may suspend the whole thing from the bonnet catch while conducting the test. Another small hole in the neck of the bottle is needed to allow air to escape. This second hole is handy to put the other end of the pipe, when testing is over, so not spilling fuel everywhere.
    Larger bottles will exaggerate the test result, but four or six 500ml bottles could weigh up to 3kg when full and make a vile mess when the welding wire gives way. Oh... obvious point I missed, four bottles = four cylinder, six bottles = six cylinder.
    One last thing, I have proved function several times with this method, but I've had to reach for the engine degreaser afterwards, due to pipes coming adrift.

    www.remmington.plus.com
     
  2. Sprint'n'Go

    Sprint'n'Go Senior Member

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    Great post, I have had this test mentioned to me a few times and understood the theory behing it but your description makes the procedure crystal clear. It really is as simple as I suspected.

    My only problem is that my engine has 5 cylinders, what do I do :rolleyes:
     
  3. OP
    premmington

    premmington Senior Member

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    at idle the injectors will only be about 250-300bar but at full revs pressures of about 1000bar can be expected. disconnecting the fuel pressure regulator will up injector output pressure for full dynamic test. i have never done this thou, as the longer you let motor idle, the more fluid gets in bottles, the more differing levels show up.

    Merc W124 300D 1990 480.000miles
    well I am a diesel fitter!!!!!!!!!!!!!!!
     
  4. ammanant

    ammanant New Registration

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    Hi i have a mercedes sprinter 311 cdi,whenever the air temperature falls below 0 the van fails to start,i have replaced all heater plugs and relay and all is working correctly,if i apply heat to the sensor on the common rail the one nearest the front of the van it will eventually start,my wife would like her hairdrier back so can someone please help to sugest what the problem can be,thanks
     
  5. 220swift

    220swift New Member

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    i have a 2002 c class 220 that starts straight away then stops. Then it has to be cranked over and over again until it starts again. Then the same thing happens again next morning. This happens particularly when it's weather is cold. Can anyone suggest a fix for the problem because my wife's getting cranky!!
     
  6. Cole@MBS

    Cole@MBS Forum Supporter Authorised Forum Supporter

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    Your Mercedes:
    124 300 CE 24 Coupe, 209 240 CLK
    you have a injector leaking off or a air leak into the system!!!

    Some garage time is needed!!!
     
  7. 220swift

    220swift New Member

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    Thanks to the forum I have manged to fix the fuel air leak on my C220 CDi. It turned out to be the fuel line between the filter and pump..

    Many thanks, misses now happy..!!!
     
  8. viscousv6

    viscousv6 New Member

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    Your Mercedes:
    Evo VIII
    will this method work on my 1999 Transit Di non turbo?
     
  9. dieselman

    dieselman Senior Member

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    Your Mercedes:
    A diesel
    No, because that uses a distributor pump, not a common rail injection system
     

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