Sprinter Fuel Rail Pressure Regulator Problems – Poor Starting

 

The Mercedes CDI series of diesel engines have an electronically controlled fuel pressure regulator mounted on the end of the fuel distribution rail. This controls, as the name suggests, the fuel rail pressure. It relies on the seal made between a single small O-ring which is backed by a split fibre backing ring.  What happens over time is that the O-ring wears and often fails allowing pressurised fuel to bypass the valve and ebb away the required running pressure that the injectors need.  Often the problem becomes more noticeable once the engine is warm and poor starting results.

Usual symptoms for this can be laboured starting when warm and occasional non starting, if the fuel rail cannot maintain the required minimum of approximately 300 bar at crank to allow the injectors to fire.  If it is possible to monitor rail pressure using Live-Data, you may see the rail pressure dancing between 266 and 550 bar. Instability of pressure when holding a steady throttle will be the clue as to a problem with the fuel pressure control.  If you do not have access to a compatible code reader thankfully the repair is simple and not costly so easy and cheap to eliminate as a cause of poor warm/hot starting. (Under £10)

Sprinter fuel pressure regulator fault 1

Remove the upper section of the inlet manifold to allow access to the rear of the fuel rail, just under and against the bulkhead/firewall.  Identify the electrical connector and remove it, select a 1/4 drive socket wrench and appropriate small reverse torx socket and short extension.  Remove the two opposing pins on the regulator flange (left and right as fitted).  Pull out the fuel pressure regulator from the end of the fuel rail.

Sprinter fuel pressure regulator fault 2

Keeping the device clean, remove both the green O-ring and fibre backing ring from the tip of the regulator and replace with new components.  Refit the regulator assembly to the rail.  It makes it easier if you have the left hand threaded pin in place in the regulator flange mounting hole, before offering it into place. (left hand in fitting position, if standing at front of engine)  Once the two pins are re-fitted the electrical connector can be attached and the intake manifold upper half rebuilt.

Sprinter fuel pressure regulator fault 3

Back of the fuel rail where the regulator mounts (normally hidden from view)

It is important to note that a failing fuel injector can also deprive the fuel rail of its operating pressure. If you suspect that this is the case, perhaps after changing the regulator O-ring to find there is no difference to the fault then you must carry out or entrust a garage to do a diagnostic ‘leak-off test’ to prove the injector system is sound.  WARNING a failing fuel injector that is passing unmetered  amounts of fuel can soon damage the engine catastrophically, either through piston overheat or engine seizure and any suspected problems must be investigated promptly!  See this interesting and descriptive forum post regarding leak-off testing.

Sprinter fuel pressure regulator fault 4

Fuel rail pressure regulator seal kit part number

22 thoughts on “Sprinter Fuel Rail Pressure Regulator Problems – Poor Starting

      1. I have the 906 sprinter on a 2006 year. I have fluctuating fuel rail pressure, and the merc guys say you can’t get a kit for it, as it comes with the rail. Cost £600 plus V.A.T. So do you know if this kit will fit it?

        Thanks

        James

      2. Hi James,
        The pressure regulator on the later sprinters is sold as a complete regulator rail by Mercedes as a new part. The early ones you could take off the regulator and change the ‘O’ ring for a few pence, now you have to purchase a assembly. If you shop around you can get a good used part for about 60-80 GBP from such as Ebay like this one here. Tremendous saving on the new part price and is the route I would take, especially as there is a few other things that give the same symptoms and I for one would want to be 100% sure it was the fuel rail/reg assembly before buying one off the shelf.

        There is a known problem with the later fuel pump where the internal fixing bolts ‘loosen off’ and affect the fuel pump delivery. Often if the pump is removed from the front of the engine, the ‘nose bolts’ (which you can only get to with the pump removed) are found to be loose. Once tightened correct fuel delivery is restored. May be worth investigating. Also be doubly sure you can see no air in the hard plastic hoses from the low pressure pump to the HP pump, if so look no further! Once that is sorted (fuel filter return valve or delivery pipe O rings) you could find that is all that is needed to get you sorted.

        All the best
        Steve

  1. Thanks for this info. What year is the cut-off? I have a 2005 that my mechanic says the regulator is going out on. He said I’d need to buy the whole rail, but I see regulators on ebay that suggest they are compatible with a 2005 Sprinter. What info is correct? I’m paying the mechanic for a new injection pump, new injector, plugs, etc….
    I’d rather do this myself and save the cash if possible.
    Thanks again,
    Steve

    1. Hi Steve,
      Rule of thumb – If its the old body shape it should be replaceable as a device and not unit. Later newer body shape is sold as complete part of the rail, however it is removable from the rail and a few used items (just the valve) are creeping onto the used parts market. ie. Ebay.
      Hope that helps
      Steve

  2. Hi thank you that great to know !! As my sprinter did just that !! But after cleaning injectors it’s got worse !! EDC LIGHT came on so I suspect fuel got mix with some metal parts from the high pressure fuel pump so I’m taking that apart and see what happened

  3. hi!!
    I have a big problem with my clk 320 cdi 2005..
    remove the diesel pump for repair losses diesel and when i have reconeccted everything in my car,the problems start..
    the car start and only maintain 400 RPM and releases a large amount of white smoke.
    you talk about some problems of bolts internals……could you explain better?
    very very thanks!

    1. Manuel,
      The bolt problem is to the pump rear impeller section, they become loose. There is more chance that fuel supply is poor – check fuel feet to and from the filter, also check and double check the O rings on the clear plastic pipes feeding the HP pump from the LP pump.
      Regards
      Steve

  4. Hi
    Need help, I have Vito 2004 115cdi w639. Today the van cut off while driving, engine light came on parked on side of road tried to start after two minutes it started prefectly. Drove about another 4 km same thing happened. It continue four more times before I could come home
    Need help plz
    Alam

    1. Alam,
      Could be a number of things, most usual would be an electrical problem/faulty sensor with crank sensor (or synchronisation with cam sensor), this would cause the engine to die and flag a fault light. Poor fuelling usually allows idle but once you accelerate engine dies off, so not thinking fuel related, especially as it restarts.

      Best bet is to get a fault code read as this will indicate the source of the issue as it will have stored the fault code in the ECU.

      All the best
      Steve

  5. Hi Steve
    Thanks for prompt reply, highly appreciated.
    My mechanic put the car on computer, two fault code 2017 and 2051 (low pressure in common rail system) he checked every thing and changed air and diesel fuel filter and
    clear codes. Took it for test drive (50km) no issues.
    On my way to home took highway van died, wait two minutes restart prefect, drove it
    abou 40 to 45 k on highway speed over 100kmph no issues, as soon as I took exit it died
    again.
    I think the van speed under 60 to 80 kmph dies and go in limp mode over 90 or 100 kmph
    Runs perfect.
    Called mechanic he said next step to change diesel rail which come with sensor next step
    Is to change hp diesel pump along with fuel pump in tank and…..
    He is talking never ending costly repairs
    Your option plz ??

    1. Hi Alam,
      He is on the correct lines with his assumption however the sensor combined in the fuel rail is an expensive part and if available a used part (or sensor that someone has removed from a used rail) that would be the best way to go. If any fuel blockage was present you would have a reduction in power and feel the engine dying away (starved of fuel) before it cut out. I don’t think this is the case. There could be a faulty injector that is depressurising the rail, either having a cracked body or faulty internal parts. Check your oil level and see if it mystically rises over a few hundred miles, this would be an indication of any over fuelling by one or more injector and washing diesel into the oil as blow by.
      I would be very cautious going down the expensive route before doing either an injector leak off test (google or youtube to discover how this is done with four pieces of plastic tube) and last but not least by making sure I has a genuine Mercedes diesel filter fitted. Fram and the like are notorious for using different internal filter material that can restrict fuel flow. After this you are down to pure fault finding.
      Ask your mechanic to monitor live data on the High Pressure circuit, if you are reading about 270-350bar minimum at 1000-1200rpm spot-on, a great deal more than this and the sensor could be measuring out of range. Both of the codes your guy gave are generic codes that would be further drilled down with a Mercedes STAR or compatible reader – I guess he is using something much more universal. Live data will be your biggest help as it shows whats going on in real time and may help to pinpoint the issues.

      I presume that restarts are without problem and no extended cranking is needed to get the motor back into life after an ignition cycle.

      Good luck,
      All the best
      Steve

  6. Hi pal I have a similar problem with my 08 315 sprinter that is starting up cold no problem but after a while running takes longer & longer to start! Had new key port installed & still same as I was told that’s what it was! Any ideas mate it’s driving me mad.

    1. Hi Lee,
      It could be fuelling, maybe a worn injector or failing HP fuel pump. Best bet is get a good independent with the right code reading tackle to give it a diagnostic session. Live data reading of fuel rail pressure cold and hot should be a good first start.
      All the best
      Steve

  7. Hi Steve

    Just an update, new code came up y94 sensor/Valve faulty, goes on HP
    clear all codes test drive for 20k it’s not cutting while driveing, tomorrow
    I will post again.
    Just one question, the Valve we replace was used it has two rubber rings
    was not available at dealer so we bought the generic rings from local
    parts shop. Must I order Oem rings and replace with generic once ?

    Thanks
    Alam

    1. Alam, If that is the long tower device on the triangular HP pump, then the purpose of that is to shut off one element of the pump if fuel pressure raises dangerously high. Check for damaged wiring to this and also in the main loom back to the ECU. I am unsure regarding the O rings. I have always taken from BOSCH rebuild kits and although some are white in colour (some purple) I cannot say if they are anything special. Certainly I would not expect them to cause a problem in the short term to prove/disprove any problem you may have.
      Regards
      Steve

  8. Hey Steve,

    My van broke down on the motorway the other day. When you spray easy start into the air intake manifold the van keeps running as soon as you stop spraying the engine cuts out. So obviously its a fuel issue.

    How can you tell if it’s the high pressure pump or low pressure pump? Or the fuel sensor on the end of the rail? is there anything I can do manually to cross any of these of the suspected list?

    One last thing, a guy came out just before this happened to drill a snapped injector bolt out, so I removed the injectors and found that there was some metal filings on the injector tips. Some metal from the drilling has definatly gone into the combustion chamber, is this really bad or will the filings just blow out of the exhaust?

    Thanks.

    1. Hi Berrera,
      Should be OK with the filings most should burn off and be blown out once it fires up. You would need to look at live data to see what was going on in detail using a compatible Mercedes Sprinter code reader, this is pretty much your eyes and prevents unnecessary parts swapping. Check fuel delivery and for leaks in fuel supply and return lines as primary fault finding exercise.
      Hope that helps a little,
      All the best
      Steve

  9. hi Steve
    i am having a problem with my sprinter 311 cdi. on cranking the rail pressure dances between 70 and 150 bars according to diagnosis machine… when i remove the rail return pipe it has diesel coming from it. even tho the pressure is not yet enough in the rail. i have removed the rail pressure regulator and it is measuring fine (resistance) are there any visible movable parts on the valve that i should see and how do i test it to see if it is working properly?

    1. Hi Farai,
      If you have not blanked off the injector feed pipes then your test proves very little. It is entirely possible you have a failed injector that is leaking past and allowing the rail pressure to be a sub-starting value. Conduct an injector leak-off test and make 100 percent sure your injectors are sound.
      Hope that helps
      Steve

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