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W209 CDI wont start after injector seal change

Discussion in 'Engine, Drivetrain, Fuel and Exhaust' started by mr spanner, Oct 15, 2012.

  1. mr spanner

    mr spanner Member

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    I wonder if anyone can explain why my 2003 CLK 270 CDI won't start since I have removed one injector to replace the leaking copper washer.

    I think this is a fuel problem just because I can't think of another explanation. I know these engines can need quite a lot of cranking to get the fuel pressure up when the fuel lines have been opened. I have changed the filter before and I remember it took quite a while to get the engine started.

    Prior to the injector removal it started and ran fine. I had just taken it for an MOT after having put some Wurth additive in the tank to get the emmissions down.

    Can anyone tell me:

    Do the solenoids on the injectors only open if the sensor on the common rail senses high enough pressure?

    If one solenoid does not operate does that stop the engine starting?

    The resistance of the solenoids (the two I measured are 0.3 and 0.5 ohms) I assume that is normal? There is another injector leaking that also needs the seal replacing but I planned to do one and see how it went prior to doing the next one.

    I know I have diesel in the common rail and the pump can pump it to the injectors. What I don't know is whether the pressure is high enough.

    I am wondering if the pump is worn and was able to maintain the pressure before doing the work but cannot build enough to raise it passed the sensor threshold.

    It seems unlikely this would be the case but I can't think of another explanation.

    I have tried cranking the engine over and over and I have primed the pump with a hand primer. As far as I can see the air is out of the system. I can use the hand primer to push fuel through the high pressure pump and the common rail into the injector pipe so expelling the air. There is no firing at all which I think is to be expected if the pressure sensor in the rail is not seeing high enough pressure.

    I appreciate anyones advice before I begin removing the lift pump and getting it tested.
     
  2. Uncle Benz

    Uncle Benz Senior Member

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    Take a close look at the injector electrical plugs for a bad connection. The engine will not fire unless all the injectors are plugged in.
     
  3. OP
    mr spanner

    mr spanner Member

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    All injectors are plugged in (all the plastic latches are down) and all look to be in good condition. I really don't think it is a connection problem.

    If one wasn't making contact does that stop the engine running?
     
  4. WG M-B

    WG M-B Senior Member Authorised Forum Supporter

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    What about the camshaft sensor toward the back of the rocker box. Is the plug home properly???
     
  5. Uncle Benz

    Uncle Benz Senior Member

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    Yup.

    Sometimes if the seal has been blowing a while the insulation degrades on the wiring. Wires shorted together will stop it running too.

    Any fault codes?
     
  6. OP
    mr spanner

    mr spanner Member

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    There are no fault codes showing.

    I have checked all plugs are pushed home but I am going to check again just to make sure. I am not aware that I disturbed that one at all.
     
  7. WG M-B

    WG M-B Senior Member Authorised Forum Supporter

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    If no fault codes you cannot have an open circuit. And changing one injector seal should not cause a starting issue either. Are the plastic fuel pipes full of fuel???
     
  8. Uncle Benz

    Uncle Benz Senior Member

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    Faults with the wiring or plugs will show as a fault code. Perhaps it is an air problem. Are any of the Plastic fuel line terminations damp? Particularly look around the smaller lift pump on the front of the engine.
     
  9. OP
    mr spanner

    mr spanner Member

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    I have only seen fault codes after the engine light has been on.

    If plugs are removed and then a start attempted would a fault be logged? Or does the log only occur after a successful start?
     
  10. Uncle Benz

    Uncle Benz Senior Member

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    It will log fault codes if the engine doesn't start. (provided it is something that the ecu can see that is preventing it starting. Air in the lines cannot be seen by the ecu, so you won't find a fault code for that)

    Edit to add, prolonged cranking with air in the lines *might* log a code for low rail pressure...
     
  11. OP
    mr spanner

    mr spanner Member

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    There is plenty of fuel getting to the pump. When cranking if you take off one of the unions the fuel is pumped out. I am not sure whether the pressure is high enough though. With unions closed and 20 seconds or so of cranking it wont start.

    I guess the next step is to measure the rail pressure. Are there gauges around designed to do this? other than using the STAR diagnostics.
     
  12. Steve@Avantgarde

    Steve@Avantgarde Forum Supporter Authorised Forum Supporter

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    Do not open the fuel system when cranking, doing so allows air in, drops the rail pressure below 150bar and the ECU will cut the fuel supply to the injectors anyway and it will still not start!! You cannot do this on CDIs to check fuel pressure. You need to use a fuel pressure tester or STAR diagnosis actual values function. You could be creating your own problem.

    Try a bit of easy start on cranking. If it starts I would suggest high leak off on the injectors and again make sure the connections are fully home
     
  13. OP
    mr spanner

    mr spanner Member

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    Thank you for your advise. I have tried cranking with all ports shut as I am aware that the rail pressure needs to be maintained. I haven't tried easy start, I didn't want to introduce an uncontrolled explosion that could be damaging? I guess this is supposed to have the effect of turning it over faster and therefore getting the rail pressure up.

    What do you mean by high leak off? I presume you mean the leak off of excess fuel through the top of the injectors. Why would that be too high?

    Can you advise exactly when the fault codes get logged and recorded? For example if you try cranking with one of the solenoid plugs removed does this generate a fault code? It does not seem to be stored. With the tool I have only faults resulting in an engine light on seem to be displayed?
     

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