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ML270 engine won't start

Discussion in 'General Mercedes-Benz Related Discussion' started by Nickvdm, Jan 12, 2018.

  1. Nickvdm

    Nickvdm New Member

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    Your Mercedes:
    Ml270 cdi 2004
    Hi, we own an ML270 CDI yr 2004. We started having problems (difficulty to start & then stalling while decelerating). Once, after stopping for a break on a long journey, it took 20 mins to start. We then took it to a Mercedes Benz dealer for servicing & to review the problem. It came up with fuel injector faults (? Not sure of actual codes) & they changed relays around to attempt to fix. The next day, after driving home it stopped in mid-drive, at 60kms/hr & would not restart and has not since. Mercedes then diagnosed it as an air leak between the intake manifold & engine block and $5000 to fix. We did not go ahead. We have since (at home) taken the engine apart & replaced the gaskets on the intake manifold, but it has still not started. Further, he has: a fuel leak-off test on the injectors; the high-pressure fuel pump & the fuel pressure regulator. The regulator & injectors gave minimal returns, but the hug-pressure return line delivered 60ml of diesel over 60secs. Does anyone know if the internal engine computer detects a fault, does it bypass the fuel pump - is that normal operation? Or do you think there is a problem with the high-pressure pump? We would appreciate any advice please.
     
  2. mercedes13156

    mercedes13156 Senior Member

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    Location:
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    Your Mercedes:
    CLK 200 Cabrio and a Ford Kuga
    Are you saying that you've tested all of these items and found them OK? Try looking for a loose electrical connection on the top of the engine, or a broken wire that has intermittent contact. Click the connectors off one by one, give both ends a scoot with contact cleaner and click them back on again. Crank the engine after each plug is treated.

    I had a nightmare trying to start mine. It would crank but not fire. I had accidentally moved a connector on an injector that hadn't been clicked on properly by the previous owner. The diagnostics showed an open circuit on that injector. Click! Vroom!

    You never know.
     
  3. OP
    Nickvdm

    Nickvdm New Member

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    Thanks very much for the advise mercedes13156.... I will try that out. One question I do have is, is it normal operation for the high pressure fuel pump to have a continuous flow of diesel through the return to tank line.... the return from the injectors and common rail pressure regulator were minimal.... but there seemed to be a lot of fuel coming out of the hp pump return to tank line.
     
  4. mercedes13156

    mercedes13156 Senior Member

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    Your Mercedes:
    CLK 200 Cabrio and a Ford Kuga
    Someone more experienced like Steve from Avantgarde would know a lot more than I do, but as far as I can recall, the fuel is drawn up by a low pressure camshaft mounted pump (just above the HP pump) and circulated through the low pressure side of the HP Pump back to the tank via a block mounted heat exchanger. The HP Pump takes a supply from the circuit and compresses it to about 300 BAR into the common rail. The injectors are opened electrically and allow a 300 BAR squirt of fuel into the upstroke. The leak off pipe at the top of the injectors collects any excess fuel, normally a trickle, and delivers it via the black braided pipe into a banjo connector on the rear of the head and this returns it to the tank for recirculation. You should be able to follow the process on the engine. Again, if I recall, the supply from the tank pops up at the rear of the engine on the right in a black ribbed plastic pipe with the clear plastic fuel pipe inside. it runs across the top of the fuel rail and into the LP Pump. From there it runs to the bottom of the HP Pump and then back up to the heat exchanger and back to the tank. all of the Low Pressure pipes are in plastic. From the bottom right of the HP Pump there is a steel pipe which runs to the Fuel rail and from the rail, there are five kinked pipes leading to the injectors.

    The low pressure pipes all have rubber o rings to seal them and they wear with the vibration of the engine. They flatten off and eventually suck air into the low pressure circuit when it cools down. Once that happens, it's a sh*t to start from cold. The answer is to replace all of the o rings. Then when you get it started it should self bleed. Problems with the HP pump are usually associated with fuel leaking out of it. You can get a scrapper or a refurbed pump quite easily and they're dead easy to replace. I assume the "hug" pressure pipe delivering 60ml in 60 seconds is the black braided leak off pipe, if not, you're referring to the low pressure plastic return pipe. that will deliver an awful lot of fuel in a very short space of time. I had one crack on me and it was scooting everywhere. Even if you have one dicky injector and everything else is OK and electrically connected, it should at least try to fire up.

    Finally, where are you? One of the other guys will be able to recommend a trusted garage anywhere the UK and beyond.
     
  5. OP
    Nickvdm

    Nickvdm New Member

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    Thanks again Mercedes13156..... sounds like it is pretty normal (this is my first time dealing with common rail deisel engines so a bit of a learning curve). Other people I've spoken to have also suggested an electrical fault of some kind so I will continue to investigate down that path.
    I'm located in Sydney Australia, so I will have to find a local European car garage.
    Once again thanks for you help
     
  6. Steve@Avantgarde

    Steve@Avantgarde Forum Supporter Authorised Forum Supporter

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    Your Mercedes:
    Mercedes-Benz C32AMG, SL55AMG, C320CDI Sport Edition Estate and SLR McLaren Coupe Roadster.
    First question,

    Do you have fuel pressure from the lift pump (3 bar ish) - if yes - Do you have fuel pressure from the high pressure fuel pump (289 bar no less than 150 bar on cranking)?

    You will need a fuel pressure tester and a sealed system to be sure. But its the first place to start. A diesel engine without the right fuel pressure won't start no matter what you do to it.
     

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