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)
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.
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.
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.
50 thoughts on “Sprinter Fuel Rail Pressure Regulator Problems – Poor Starting”
Done this now runing properly thanks for the info nice one
So glad it helped you out.
All the best
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?
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
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.
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
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
Sounds like the HP pump is probably the culprit.
Let me know what you find.
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!
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.
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
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
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
I think the van speed under 60 to 80 kmph dies and go in limp mode over 90 or 100 kmph
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 ??
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.
All the best
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.
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
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 ?
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.
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?
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
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?
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, we have an issue with an 2010 2500. Seems to have fluctuating fuel rail pressure at idle. We are seeing 195 bar to 211 bar at idle. I am under the impression I should be seeing 300. We recently did the turbo base gasket, oil cooler and seals and the rear main seal / plate. During the repair , we replaced the fuel filter also. Everything went back clean and leak free. Owner drove vehicle 65 miles without issue. Next day encountered a long crank before start and drove about 5 minutes. Check engine light came on an reduced power due to limp mode. Code was 11bd00. Is it possible that this vehicle with 190,000 miles had the pressure regulator take a dump on us while doing this repair? Specifically, having the fuel system open and then having to repressurize? Customer is having a hard time understanding this possibility. We could not have damaged the regulator doing these repairs! Any help would be much appreciated. Thank you.
Check the fuel delivery, long crank could be air in fuel, especially as rail pressure is on the up and down. The Low pressure pump may be delivering air into the HP pump that is fluctuating. Make sure all the lines you could have disturbed are back in place and clamped correctly. Bin off any jubilee clips and get the correct hose clamps if not fitted. Check the fuel filter delivery pipe for splits and the o rings that seal the rigid pipes to various points on the delivery run. I am betting if you pull back the protective black cover on the centre pipe on the filter body you will be seeing air bubbles when running.. This air in fuel will trigger limp as there is insufficient delivery pressure.
All the best
my sprinter 308cdi just cuts when driving 200m, 300m, 400m but when it stops i put quick start and it starts and drive the same distance please help am stressed.
Sounds like fuel delivery problem, check all lines and make sure there is no leaks allowing fuel to run back to tank.
i have a 2002 308 cdi sprinter i replaced the oring in the fuel pressure regulator due to a starting issue 2 days later i have the same problem but it will start after some time
any ideas where i should start looking
It sounds as if fuel is running back to tank and there is a leak in the fuel delivery system to air. The first thing to change is the filter for an OEM unit without water indicator (these often leak and are best avoided). Check all pipework to the filter and also the O rings on the clear pipes to the High and Low pressure pumps.
All the best
Have a 515 cdi sprinter 2009 have put 3 high pressure values on injector rail in last 8mths
Gone again any ideas goes on to limp mode machine states high pressure value
Have injectors tested as one may be leaking back compression gasses from the cylinder back pressuring the fuel rail.
My 2004 – 318cdi Sprinter has developed cold start issue. Noticed air in plastic fuel lines. Replaced HP fuel pump 8 months ago due to failure, so have now replaced all plastic hoses (OEM). Engine will not start & noticed still large amounts of air pumping through plastic hoses & LP pump seems to pump little pressure. Could it be the LP pump or do you have other suggestions ?
Engine fires on a spray of easy start, but will not continue.
Replace fuel filter with correct Mercedes part and replace the black plastic non return valve on the top of the filter canister. If you have a water in fuel sensor type of canister exchange this for a non sensor type and tape up the sensor. This may help you out as often the main culprit is the o ring seal on the plastic non return valve or Water in fuel sensor.
HI Steve im getting a fault code p0193 fuel rail pressure circuit high input(bank1) the engine light is on i have replaced the fuel sensor and the regulator can you please give some advise
Could be a faulty injector allowing the rail to be pressurised from the compression stroke?
My 311cdi has two leaking injectors would this be the cause of my poor starting? It runs great but struggles to start
Any leaks will result in lost compression and without doubt will make starting harder.
2005 sprinter 5 cyl.
New fuel rail.
New intank fuel pump.
Still no power.
Will not pass 3000 rpms.
Code reads 2021-1 (rail press is too low)
Check clutch switch and brake switch above pedal box.
Best Regards Steve
Hello I have a 2003 sprinter starts no problem and ticks over but Edc light comes on and stays on I would be grateful for any advice thanks
It could literally be one or a selection of things. You won’t know until you get a code read to at least give you a starting point. Hope that helps!
My 2008 Sprinter 311CDI suddenly cut out whilst driving and wouldn’t start again my mechanic plugged it in and there is no fuel pressure registering there is a good supply coming from the low pressure pump so the high pressure pump was removed and tested by a specialist result being the pump is good,what would you suggest we try next?one thing that did show on the diagnostic machine was a faulty crank sensor which was renewed but the machine is still saying incorrect signal from crank sensor but my mechanic says this will not effect the fuel pressure?
Hope you can help.
There may be an issue with the cam sensor. The crank and cam sensors work in tandem to time the injection system. If there is a recorded Synchronisation Error code this will hold off the fuel pressure and prevent starting. Fuel pressure is cut if there is any factor occurring with the engine controls that could cause damage.
Hi .. I have a problem with the Viano 3.0 cdi 2007. After changing the fuel filter, the yellow engine fault warning light comes on and the fault is 2020-001 .. which is the most likely fault: pressure regulator carill, or flow regulator by the low pressure inlet? Thank you very much Regards
Start by replacing that filter with a genuine MB part, often there are different filter screen sizes in the aftermarket ones, if there isn’t a leak or something similar on the replacement then try fitting a genuine part with new seals.
I have a 2500 2011 sprinter Mercedes-Benz it was running good no lights o advice, I park go to the store get out and don start, check, high pressure pump, pump fuel, good ,but cut the fuel suply and don’t starts any advice ,thanks
Be sure there is no problem with the key and its key coding. Try the spare key an see if that works correctly.
i hope you can help me as i see you hava e loot of experience. i hav MB B200CDI,W246, year 2013. I have error code P025218. When i erase the code, car goes ok for 10 miles, and then engine light goes ON again, and I have the same error code : the output for the quantity control valve has malfunction. Otherwise motor is runing smothly without shaking or strange noise, only the power is reduced.
Can you please give me some advise.
Thank you in advance.
I guess you will need a new High Pressure diesel pump to rectify this. The Quantity Control Valve sits in the High pressure fuel pump.
Hi…I am in France with a 316 5 cylinder diesel sprinter and I have identified that the pressure relief valve o ring may be the problem with starting when cold…no fuel pressure…and the longer you leave it when it has run the harder it gets to start…but it always starts..sounds like a leaky o-ring. Done everything else and now focussed on this. I have the service pack for the seals. You mention…and there is in the pack…a fibre seal. Before I take the thing out and drop the fibre seal which I am certain to do…where is the fibre seal located. I cannot see one on your images..you say “o-ring backed by a fibre seal” but I cannot see it. Can you enlighten me please. A mercedes specialist said he had never replaced the fibre seal and didn’t know what it was for and I could miss it out–not so sure.
The fibre seal is at the back of the green o ring as pictured.