I had an interesting fault to deal with the other day on a 2004 (T1N) 313 LWB Mercedes Sprinter. The driver reported that the van would not go above 70mph and the ‘fuel filter clogged’ light was illuminating. Switching off and on the engine cured the fault, until trying to attain over 70mph where it would fail again.
The first port of call was to check the fuel filter, as if its badly choked this is the ‘bog-standard’ Sprinter fault with dash ‘check filter’ indication just to compliment the issue. This item was replaced a week or so earlier during a normal service and a genuine MB part was used. What is more this would have been the first item to have been thrown away, suspected faulty even when new, of being the wrong flow rated item if it was not of MB manufacture… So it was not that.
Read fault codes were: ‘Fuel delivery pressure not as anticipated’ and ‘Fuel delivery pressure low’. Sure enough if you maintained a constant 3500rpm with the vehicle stationary, after about 30 seconds the revs began to drop to about 2000rpm and immediately pulled back up to circa 3000rpm, all repeating in a one or two second cycle. Idle was normal, regular and unaffected. Inspecting the clear LP to HP pump fuel delivery hoses – all looked perfect with no visible air circulating, all the connections to the filter including the non return valve and supply checked out fine.
I suspected, against my better judgment, that the low pressure fuel pump had developed a fault. Strange, because I have never replaced this item on any of the Sprinters I have had through my hands and perhaps this was going to be the first! Disbelieving it could actually be the low pressure pump, I checked the from-tank fuel delivery hose and blew back the line with low air pressure to prove the flow. This was fine too. So lets change the low pressure pump…
To change the low pressure fuel delivery pump first remove the top turbo hose to gain unrestricted access to the area. Release and pull off the hard black vacuum pipe that serves the brake servo and tuck it out of the way. Now undo the two reverse torx head bolts that hold the vacuum pump to the cylinder head. You can use an 8mm multipoint socket if you do not have the appropriate tool. Take care, as one of the fixing bolts also supports the dip stick tube, make sure you twist this tab carefully out of the way so as not to foul the vac pump as it is withdrawn.
Now with a straight controlled pull remove the vacuum pump from its recess in the head, noting how it engages in the cam shaft and the orientation of the coupling, as this will have to maintained to allow you to refit the pump later. Once the vacuum pump is out of the way the low pressure fuel pump can be fully accessed to the right. Next the input and output fuel pipe unions have to be released and withdrawn from their spigots. This is achieved by pushing back the white plastic forks on the snap fix unions and twisting them carefully out of the pump housing ports. Tuck the two pipes out of the way, making sure that the unions are kept clean and not damaged in any way while you work.
The low pressure fuel pump is now removed by taking out the two remaining reverse torx housing screws and withdrawing the pump from the cylinder head, in much the same way as the vacuum pump, noting the position of the drive coupling. The replacement pump can be fitted in an exact reversal of dismantling, along with the vacuum pump and finally the servo vacuum and turbo hoses.
Since you have probably lost some fuel in the lines, possibly you have fitted a new dry-pump be prepared for a delayed start of the engine. Usually it fires immediately on turning the key then dies. This is to be expected, keep turning the engine over and within 10 sec or so it should fire. If not, wait for a minute and then try the starter for another 10-15 second burst, repeat until it fires which should be well before the third try. Do not ‘hang’ on the starter for long periods, this does no good to either the starter or battery and is best avoided if at all possible. If it doesn’t start, check your work. Make sure you have not damaged any O-ring seals on the click-on fuel unions and that are connected correctly.
The Sprinter fired up on the second pull and ran wonderfully, I sat with my foot on the throttle, holding revs steady at about 3500rpm – at about 30 seconds into the test the revs dropped and the whole pulsing/revving cycle began again. Well, my gut instinct was right about the low pressure pump, it wasn’t that either!
The only thing left to replace was the low pressure fuel sensor, this lives beneath the inlet manifold on the right front as looking in. It is tee’d into the low pressure, hard plastic clear fuel line on the LP pump output. Once the electrical connector is released, it takes either a large deep socket or a big ring-spanner/adjustable to crack and remove the sensors taper fit union and unscrew it out of its receiver, make sure you observe and recover the small aluminium seat washer that slips over the brass thread on the sensor, as sometimes this sticks to the casting. Because the sensor is inverted the seal cannot always be seen to be stuck on the receiver, and the last thing you want to do is to fit a new sensor with new alloy washer while the old one is still in place!
Needless to say, once the van was restarted the fault had been cured. Although not completely faulty, the sensor must have been signalling incorrect pressure readings back to the ECU that was cutting the engine, when the LP pressure measurement reached its switching threshold, the engine picked up again and the whole vicious circle ensued.
Hopefully this section has given you an idea of things to check if you have a Mercedes CDI diesel engine with similar issues. Things to check in order are: Filter, fuel line connections/condition, blocked delivery pipe from tank, fuel pressure sensor and last – Low Pressure delivery pump!
31 thoughts on “Low Pressure Fuel Pump – Mercedes Sprinter Surging Engine – Will not go above 70mph”
Thank you for this description. It will likely be helpful talking to mechanics.
Can you give me a part number for the fuel pressure sensor / low pressure fuel sensor? Does it cost around $265, which is what one place thinks might be the part, but no one seems familiar with it? I am not in the UK, so can’t have you fix it.
Hi there Carole,
Please understand this is a part number for the UK part for a Euro 4 cylinder engine. It may differ to your model/country but here goes: A004 542 16 18 The cost for a non-MB OEM part is about $80.00 see here
All the best
Hi Steve Ball, Thanks for replying. We replaced the part. Unfortunately, that was not it, so it went in to a Mercedes dealer and their analytic machine decided it’s something with the transmission, which is now fixed, but now they cannot get some kind of computer working right.
I have a Mercedes vito diesel van which cuts out whilst driving. It restarts no problem then will cut out again. I have had the fuel pump replaced.fuel filter,camshaft sensor replaced.Took it to Mercedes for diagnosis after 3 weeks they now say it’s swalf in the fuel tank and to rectify the problem the whole fuel system has to be replaced.Can you possibly help me out on this issue. Many thanks Ron
There is a known issue with the wiring loom to the injectors, if one of the wires shorts to the cylinder head/rocker cover it shuts off the ECU and the engine dies. See here,
Its well worth investigating and if you can get to the loom section in question slip some cut up lemonade bottle plastic under the loom to further insulate it from the surface beneath. My money would be on electrical problem if it restarts no problem. It may also be the crank sensor that is giving issue, this runs in synchronisation with the cam sensor and could give rise to the symptoms you describe.
All the best
Thanks for this guide, it’s just what I was looking for as the Haynes on removal of the LP pump is wrong.
My 2001 2.2 311 was running perfectly for ages, after refuelling with some slightly dodgy (dirty container but filtered) fuel I drove about 5 miles and then the engine started acting as if it was starving, firstly at top speeds it was loosing power and then by the time I got into town it was down to only running with my foot to the floor, would stall at idle and then it stalled completely, to me it seemed like a more gradual version of the symptoms of running out of fuel.
So “ok” I thought, “you idiot Duncan”, dirty fuel has probably blocked the filter, got a new filter, replaced, refilled and re-sealed, no joy, van would crank and almost run on one cylinder (sounded like it anyway) and then die as you stopped cranking, that’s the best it got. Next I stripped the tank off the chassis, took the fuel lines off and blew both of them out, there was some restriction in the return line, probably in the cooling coil, but a bit of isopropanol and a compressor I blew that restriction clear.
Re-assembled everything, cranking and nothing, topped up filter twice, still nothing, I can see fuel going in and out of the low pressure pump and some fuel is going down the return line but no fuel is coming up the feed line, could this be a faulty LP pump? I am at a loss.
Hi there Duncan,
Obviously I would be checking my work and making sure all seals on the hard plastic pipes were doing their job.
If all that looked good then I would be looking at a blown or passing seal on the pressure regulator control valve at the back of the fuel rail. It is just worth checking the ECU fuse hasnt blown for reassurance that all is well in the electrical department.
Hope this helps.
Thanks again Steve,
Both lines are sealed, eg. if I put a bit of clear pipe on the end of them and suck I see fuel rising out of the tank, and with my thumb over the end the fuel does not drain back down.
ECU fuse is fine, so I am now going to pursue the Pressure Regulator as you suggest, in your experience is it usually a case of replacing the o-rings or am I better off buying a new part and o-rings?
Many thanks for your help, you are pulling me back from insanity 🙂
Its easy to do the O-rings and costs under a fiver. The only issue is access is tricky at the back of the fuel rail, its a fiddle put possible. It may be worth taking your VIN to the dealers when you go for the O rings as there were some later models made with a different pressure regulator that unsurprisingly has non-replaceable O-rings!
Hope that helps
All the best
Well Steve, your instinct was right, I could see a v in the green o-ring where pressure had been bypassing the pressure regulator control valve. So I replaced all the rings on it, still wouldn’t start. I had a spare LP fuel pump, so I put that on, still wouldn’t start.
So I am now at a situation where the engine will turn over for a while, and it will emit thin clouds of unburnt diesel vapour from the exhaust, ie. it feels like it wants to start, but is not getting quite enough fuel pressure to combust the vapour. Admittedly I am clutching at straws now and this is only a theory, but all I have left to point the finger at is the High Pressure Pump, unless you can suggest anything?
Both ECU fuses are still fine, I had the codes read at the start of this process and it was reading low pressure, and a mixed bag of older codes, so we cleared the codes and even after cranking for a long time on and off yesterday, we now get no error codes.
Am sorry to bother you with this, but I live in the remote reaches of NW Scotland and getting hold of anyone that has experience of merc engines is not easy.
Hi, great site. For a number of months now I have been experiencing an intermittent fault of non starting, e.g, 9 times out of 10 it starts and runs fine.
311 cdi 2004, recent work includes May 2016 2 injector seals replaced, and 4 glow plugs renewed, April 2016, water system refilled after replaced metal bar beneath radiator, February 2016 (perhaps significant) the fuel tank holding straps had to be replaced as the tank was hanging down, prior to this the van was experiencing a boost problem where for about 3 seconds the engine would not respond then returned to normal. Since fixing the straps that has gone away but still this intermittent non start, having to resort to easy start. I dont know how long the tank straps were broken for.
Someone mentioned it was perhaps drawing air and the tank being displaced might have been a factor. In March the fuel filter replaced.
Ps sorry, forgot to mention also replaced the seals on the rail at the back about 4 months ago as it was doing it then but very rarely. The oil light also comes on and stays on but level fine.
I wonder if there is a break in the engine loom that is causing a short, the place to check is the section that drops from under the inlet manifold down past the engine mount. Cut back the braided outer and inspect inside, on occasion the engine mount wears through the loom if it is not secured correctly. The intermittent non start could be electrical, possibly an injector cable or fuel reg/ pressure sensor line.
Worth a look, but I would not discount a faulty oil level sensor in the base of the pan and an O ring/non-return valve issue as previously described.
There is a non return valve on the fuel line on top of the fuel filter canister. This or its ‘O’ ring can become faulty and allow air into the system causing fuel to run back to tank. Also if any of the ‘O’ rings on the hard clear pipes from the low pressure to high pressure pump are hardened this can have a similar effect, often intermittent due to temperature/pliability of the seal. The black non return valve and O rings are a cheap thing to replace and although a bit of a fiddle often fix this kind of issue.
Let me know how you get on.
All the best
Hi, thanks for your reply, I have not sorted it yet but I can supply some more info. The van starts most of the time but more and more it won’t start, its the same hot or cold. When it decides not to start after a few seconds of cranking the EDC light comes on. I use the ether start and it starts, sometimes the light stays on but mostly not. In the clear pipe on the filter I have noticed large single bubbles.
Obviously the bubbles are not good, and the few things previously mentioned should address those. Electrically there could be a couple of things preventing regular starting. Cam or Crank sensor. The can sensor is above the starter motor on the edge of the casting that bolts engine to the gearbox. When it cranks you should see a small flicker on the tach needle, if you don’t get this during the starting cycle suspect the sensor. Again there may be a synchronisation error caused by the cam position sensor being faulty, this is on the back of the rocker cover and picks up signal off a point on the camshaft. Address the seals/air in the system fist before looking elsewhere.
All the best
Hi we recently brought a year 2000 Mercedes Sprinter 313 CDI manual took it on a 7 day trip all seemed good until our last day when all of sudden it just dropped speed from 100 to 80 and would not go any faster even when I had my foot flat on the peddle. The previous owner indicated that he had once the same problem he said it was an air intake temperature sensor that had oil on it, I sprayed it with contact cleaner and all back to normal drove home ok, no warning lights came on. Is this a comon problem do I need to simply replace the sensor. I touched the sensor & it was wet with oil, where is the oil coming from. No warning light came on. Appreciate your diagnosis.
It is normal that some oil residue exists in the induction hosework, intercooler and charge air system, this is mainly from the crank case breather system that this engine adopts and is nothing to be concerned about. I doubt the cleaning of the sensor actually cured the problem and it more likely to be something else causing the limp home. The fact you turned off the ignition and restarted the engine, this often resets the condition and you are back to normal until it happens again.
Usual culprits of limp home under full load are slight leaks in the turbo boost pipework, normally indicated with black oily staining around the leaking hose clip etc. You may get lucky in changing the induction air temp sensor but my money is on a boost pressure leak of some sort.
hope that helps,
All the best
Hi I have a 2013 c180 which comes up with fault low fuel preassure I have replaced all the injectors and the fuel rail preassure switch it still has the fault car won’t go more than 80km/h any suggestions please.
First off you need to to change the fuel filter if you have not already, as a restriction in supply will give you this warning. Delivery is obviously a problem. Have you measured the fuel pressure using live data on the diagnostic tool? Then consider low pressure fuel pump or electric delivery pump if fitted in tank. Is in limp home with EML illuminated?
Where can i find the low pressure pump on the Mercedes E320 CDI 2002 W210. I have no fuel coming from the tank meanwhile the tank is half full.
Car on cranks, but can’t start.
The low pressure pump should be at the front of the engine as shown in the article. The pump only functions when the engine rotates and relies on a sealed system to hold the fuel in the pipework until the next run cycle. Any leaks from either the hard plastic fuel pipe seals, fuel filter, non return valve or LP to HP clear lines will cause the fuel to run back to tank and prevent starting. Check all seals for leaks (fuel filter to non return valve o ring most likely culprit) Make sure fuel filter is full to the top and crank engine, extended cranking may be required to get you running if air has been drawn into the LP/HP pumps but once started the system should not leak back to tank and you will once again have reliable starting.
Hi Steve, I wonder if you can help me. I’m a taxi driver from York driving a 2001 208 cdi that I converted to take wheelchairs. My head gasket went on the 2nd Dec no warning other than it stalled in traffic but started again after being stood for 15 minutes but then stalled again after 2. the head gasket was caused by the water pump propeller becoming disengaged from the pulley. when we ran checks having found the temp gauge to be through the roof ( I have to admit to not having noticed it before the stall), we found the radiator and all hoses to be stone cold with the exception of the hose from the thermostat to the expansion tank which was red hot and under pressure. Anyway I got another engine from Prestige Allparts over in Oldham as I considered this to be the quickest remedy, taking out the blown one while waiting for the new (second hand) one to arrive. Having transferred all external components and fitted the new lump I started it with the aid it has to be said of a little squirt of easy start to help the fuel get through the system. once running it ticked over like a dream but when revved past about 1800 revs it rose and fell as if a cylinder wasn’t getting fuel and on each occasion that the engine was turned off would not start again unaided on almost all occasions. I had only replaced all for injectors on the 2nd having gone to Horwells in Stanningly and had them all top to bottom reconditioned so thought I would put the old ones back in to see if that cured the problem. It didn’t. My next thing was to check the wiring harness as they do go brittle especially around the injector plugs, as a result I have put a new harness on from Mercedes ( Northside truck and van) to no avail. we tried driving it down the road but under load (the weight of the vehicle) it has no power whatsoever there wasn’t even enough grunt to get it back up the wheel ramp in 1st. I am fast running out of money and letting wheelchair users down at a time of year when they really do need me. I would be grateful for any help urgently. the rise and fall of the revs as I said over 1800 rpm is consistent with the cycling rate of the engine leading me to discount air in the system. bearing in mind that everything that came of the old engine was working just fine and has been put on the replacement, I am led to believe that I have an engine which has little or no compression on one of the cylinders and as such is replicating the effects of a faulty injector. if you take the metering valve wiring off it is possible to start it, a mechanic friend suggested that but that is as far as it gets you. Just as point of interest Prestige pressure wash the sump and head before sending the engines out to do the checks that they do however the inlet ports on the side of the block were still very clogged with tar like oil deposits
Sounds like fuel, or lack of it.
Replace the fuel filter with an OEM Mercedes one. Replace the back non return valve on the top of the filter canister along with its O ring. Double check the small O rings on the clear pipes from the LP to HP pump. The reason it will only start on ether is that the fuel is running back to tank because of system leak to atmosphere. Sort that and she should both start and run a great! Probably that £5 non return valve or its O ring.
Sprinter cdi 208 2004 24K on the clock
Hi we have just purchased the above van to convert to a Camper its in mint condition for the year but we have a very loud knocking coming from what I think is the same part in the pic above. In the cab its very loud and is defo coming from the floor between the seats. When I get under i can feel it knocking in what looks like some sort of valve. I have taken a pic put cant attach to your web page. This noise comes and goes and does not effect the performance of the van. Can I mail you a pic any help would be appreciated.
send the picture to firstname.lastname@example.org I will take a look and post it up.
All the best
Hi am in right pickle I got cdi 110 2002 reg plob I have it used to start in a sec or two now takes lot longer to start than normally but when started runs fine well untill I get random when driving with out any warning engine dies and edc comes on turn off wait 10 secs or more and it starts up after gd few turns away I go till I accerate harder cuts out again ramdon and got worse I check fuel filter and air in line and lp pump all ok took to my bro got the kit to read ecu comes up fuel pressure senor fault which got on order but reading the forums this is rare hoping it’s gonna do the job if not what else could be causing this or causing the senor error many thanks on ur though
often the seals on the top of the fuel filter leak air into the system. A new fuel filter usually fixes the job. There is a black plastic non-return valve on the top of the filter canister replace this it only costs a few dollars and is known to hairline crack and simply fall apart inside. Changing this also is a positive step.
Hi all, very interesting and helpful comments. thanks all.
I just had a problem with my Vito 112 CDI with it cutting out due to air bubbles in the fuel line. Air bubbles were clearly visible in the centre pipe going from the filter to the (low pressure pump?).
Replacing the centre plastic pipe from the filter seemed to fix the issue.
Thanks for all your comments and thanks Steve for your ever informative suggestions and recommendations.
I had this same problem for a year and half and have been meaning to get round to fixing it but have only been using the van on local roads. I tried fuel filter and then read this article went straight to mercedes and paid £52 for a sensor and it’s cured it . thankyou