S210 diesel estate 2002, location of low pressure fuel pump?

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BobHUK

Member
Joined
Apr 30, 2017
Messages
54
Location
South Hertfordshire
Car
Mercedes E 220 diesel estate
Hello,

I have an E220 S210 Estate auto diesel. Recently the low pressure fuel pump stopped working. So now when I want to start the car I have to open the bonnet, and spray easy start or cold start into the air intake and crank the motor for about 15 seconds before it will pick up and run. Once running it runs as though nothing was wrong, but I know the low pressure fuel pump has packed up because I used to be able to hear it pumping as toon as I turned the key and before I started cranking the engine. Now that initial sound is gone.

I looked on Youtube to see how to change the pump, and there are several videos of how to get to the pump and the large canister type fuel filter that sits next to it. These are located under a plastic cover just in front of the rear axle on the near side.

So I dutifully jacked up the car and removed the plastic cover to find only a small radiator that seems to be used to cool diesel that returns to the tank from the injector line. It seems that the videos only apply to saloon cars, and estate cars have the pump mounted elsewhere.

That being the case, I now need to find out where the low pressure pump is located on my estate car, in order that I can remove and replace it.

Anyone know where I can find it? If so, do you have any diagrams or photos of where I can find it and how to get to it?

Many thanks,
 
Well,

It seems I was wrong to assume that there was a low pressure pump on a diesel. Instead the diesels have a predelivery pump that sits just above the main high pressure pump that's mounted on the front of the engine. As it is, the thing still won't go unless I spray lots of cold start into it before cranking it. Also, when a local garage had a look at it, they noticed that the fuel filter chamber was more or less empty. So I can only assume that it's having to pull fuel all the way from the tank to the predelivery pump before the engine can fire up, and the cold start helps to spin it up faster so that it can pull enough fuel in to start it.

Thinking the predelivery pump may have packed up, I took it off this afternoon, and I've dismantled it to find out how it works. It's very simple, just two gear wheels spinning against each other, like a mechanical oil pump, same kind of design. There's literally nothing to go wrong with it as long as the two wheels spin, and from what I can see, they both spin like brand new. The pump is driven by the inlet camshaft, and as that must be turning for the valves to open, the pump must be spinning as it should.

This means the problem I'm having isn't anything to do with the predelivery pump, but must be to do with the tank instead. If there's any kind of blockage in the tank, it could be causing the predelivery pump a problem in trying to suck through diesel all the way from the tank while its little wheels are turning at half engine speed. So next up is to see if I can replace the fuel tank strainer. It's easy to get to, all I have to do is empty the tank before removing it. Trouble is, I've got around 40 ltrs of diesel in there at the moment, so I guess I'll be doing some siphoning first to get as much out as I can. Then I'll put a big bucket under it and undo the strainer till it drops out. I'm dreading what I'll find when it does come out, as the car's done 179,000 miles, and this is probably the first time it will have been removed.

Wish me luck, and I'll try to keep you informed of what I find.
 
I think the problem will be with the rubber o-ring seals.

On the end of each plastic fuel pipe, there's a o-ring which degrades over time letting air in. I'd be sure this is your problem, you can tell by looking at the rubbers. They can be replaced separately and keep the original plastic pipes to save money. If you search on the forum, lots of threads that cover it.

I'd start with the two rubbers on the low pressure pump that you have already removed.

Let us know how you get on.
 
yeah, aux pump rarely fails. Suggested o-rings are most common culprit, and low pressure fuel lines itself may brittle too. You can see air bubbles running in 'clear' fuel lines if system is drawing air in. Is cap of the fuel filter tight? Then I remember couple of cases where fuel filter housing was cracked.
 
91dm and mersum1es,

Thank you both for your suggestions. I must admit the O rings hadn't occurred to me, but now that you mention it, I'll see if I can remove and replace them. I also thought about blowing air back down the fuel line to clear any blockage that might be slowing the fuel from exiting the tank.

The odd thing is that the garage where I took the car first of all, thought the fuel filter might be dirty, so they fitted a new fuel filter, but told me they were surprised to find no fuel in the filter chamber. This would indicate that the pump is having a hard time trying to suck fuel from the tank. As you say, it could be down to the O rings letting air in at the pump junctions. It could also be a combination of that and a blockage in the line. Either way, I think a trip to the main agents is on the cards, to get new O rings for the pipes. I might also fit a one way valve in the fuel tube down by the tank, so that whatever is sucked out of it can't then flow back into the tank, leaving a half empty fuel tube from the tank to the filter if the pump stops sucking.

I've had the fuel filter lid off, and put it back on again, so I know that's done up tight. As to the fuel filter case being cracked, I think there'd be fuel all over the inlet manifold if that were the case, and it's currently dry, but thanks for the warning, I'll keep an eye on it for the future.

Many thanks to you both, and I'll keep you all informed as to how I get on.
 
I've never seen a blockage in the pipe yet, always air getting in past the rubbers. Best to replace all at once if you can, be very careful with the pipes if you're just replacing the rubbers as the clips easily break.
 
91dm,

The pipe clip on the inlet pipe has broken, well the hard white/yellow plastic bit has anyway, The softer black polythene bits that actually grip the lip on the inlet of the pump are not damaged, so they should clip back on easily. The ones on the outlet pipe are undamaged (thank goodness!). However, I may try to get hold of new clips while I'm collecting the O rings tomorrow. I've ordered the O rings for the vacuum pump as well, as the manual says that if ever this is disturbed then new ones should be fitted.

If the engine is still hard to start after the O rings have been replaced then it can only be air getting in to the pump from the crankcase, or from a cracked pipe on the inlet side. Although, if it was pulling air in from the crankcase then I'd expect to find engine oil in the pumping chamber, and there's none at present so I'm hoping that it is just the O rings that have caused all the trouble.

Similarly, if the inlet pipe was cracked then I'd expect to see fuel leaking on to the crankcase when the engine has stopped. However, the crankcase is dry, so I don't think the pipe is cracked. While I'm at the parts department I may well try to get hold of some new pipe anyway and replace what's there.

After this is all done, I may well see about fitting an electric pump somewhere between the tank and the filter, so that the filter chamber is always full. You can get pumps off Ebay for around £10 - £15, and one of those will help to ensure that the predelivery pump isn't having to suck fuel, but instead it will be receiving pressurised fuel from the filter at around 4 - 6 psi. I've already got an electric pump fitted on another vehicle and that has a pressure gauge, so I know what pressure they run at.

Many thanks for your information on that, it may well have saved me from spending hundreds of pounds that I can ill afford, as I'm an old age pensioner and just have my state pension to live on, so not wealthy by any means.
 
Ooops! Just realised that the pipe clip that's broken is the one on the outlet pipe, not the inlet on the pump.
 
Fuel is not leaking always out from low pressure side... and If fuel drains back to tank it means it can get air somewhere. Sometimes injector leak connectors can let air in (circulates back to filter case), which brings one more place need to check; injector back leak test! Usually leak is there worse at cold but I remember few cases where leak was started at hot engine first (it will escalate...) and definately cause long cranking. One additional place came up my mind; o-ring of the pressure regulator valve (end of the rail) may be broken, rare thing as well. Valve and seals are not any more sold separately...
 
When you replace the rubbers, it will be a similar case of cranking before it will start. Just make sure you've a second battery/power supply. It'll be the next day before you know if it's fixed.

We fitted hand primers and electric pumps but took them off again, once the system is working, it works well without any extras.

Let us know how you get on. We've a scrap 220 CDi here and dealers usually have the pipes in stock if one completely breaks.
 
Hello again,

Someone has just suggested that the preheater element may have failed. Is there such a thing as a preheater element? I know the car has glowplugs, and the glowplug light comes on and stays on for about a minute as soon as I turn the key to start the car. So it stays on while the engine is running. It has done this since I bought the car, and I took it that this was normal, but the bloke who suggested a failed preheater element has now said that the glowplug light should only show for 3-5 seconds. Is that right?

The thing is, the car has never failed to start on even the coldest of days in the past, so why it should suddenly fail to start when the engine is already warm is a mystery.
 
Back to square one. I've charged the battery, bought new heavy duty jump leads, connected everything up as it should be, primed the fuel system by filling the fuel filter chamber to the brim, sprayed cold start into the air inlet and after cranking for around 20 odd seconds it suddenly fired up. So I put everything away and went for a test drive. The car drives as though there was nothing wrong. All cruise, acceleration and tickover are as per normal.

When I got back from the test drive I turned the motor off, then immediately tried to restart it. It took around 10 seconds or more before it fired up, but then it went as per normal once more. So I stopped it and left it for 5 minutes, then tried to restart it. It wouldn't fire after repeated 10-15 second bursts of the starter. So I sprayed cold start into the inlet and after around 10-12 seconds it started. I then turned it off and left it for about 10 minutes and tried to start it again. Nothing! It just cranks and cranks, but doesn't speed up which would indicate it's firing.

Someone on another forum has suggested the glow plug relay (controller) may be at fault. This is not a cheap item. On Ebay the cheapest listed is £64 and from a local parts dealer they are quoting £203. I haven't got round to phoning the Merc main agents yet, but when I do I expect it will cost somewhere north of £250 for a genuine one.
 
Yep, you have faulty glow plug or controller. You can measure resistance of the individual plugs by disconnecting connetor from control box. This will not always tell the whole truth but at least you will find if some of the plugs is totally short or open circuited. But that lump will start even at -20C without pre-glowing, so I believe you have separate problems. Faulty glow plugs will slow down starting a little bit, then you have fuel line leak which prevents rail fuel pressure to rise fast enough. I believe fuel pressure is the dominating reason. Do you see air bubbles running in clear fuel pipes?
 
Someone on another forum has suggested the glow plug relay (controller) may be at fault. This is not a cheap item. On Ebay the cheapest listed is £64 and from a local parts dealer they are quoting £203. I haven't got round to phoning the Merc main agents yet, but when I do I expect it will cost somewhere north of £250 for a genuine one.

I've got a spare OEM controller available, I think.
Test the GPs via the 6 pin plug that connects to the controller.
Around 1 Ohm means the plug is OK. They usually fail open circuit.
 
mersum1es and a111r,

Thank you both for your suggestions. I phoned the local Merc main dealers to get a price and availability of a new controller, and was surprised that their price was £104 + VAT, or £125, so much cheaper than I expected. As it is I've ordered a new controller that I found on fleabay for £42, so with luck that will cure the immediate problem.

a111r, I'll check the resistance of each plug tomorrow and hopefully I'll be able to find out which plug is at fault, or whether they all are. If one or more of the plugs has died then I'll see about replacing them, bearing in mind the dire warnings I've read on here about plugs snapping in the head. One thing I have noticed is that in order to get to the glow plugs I have to remove the high pressure fuel rail, so it's not going to be an easy job trying to remove them. Furthermore, I'm worried about broken plugs, so I'll be following the advice of someone else who posted on this forum, who took his out, and make sure to spend lots of time adding easit or plusgas to the tops of the plugs over a period of weeks in order to help the removal process.

As to the fuel pressure not rising quickly enough, that could also be true, although fuel is being drawn through. Furthermore, when I spray cold start into the inlet and then turn the key, it starts after about 10 seconds of cranking, so yes, if the plugs are dead then it is starting without them, but it will only do this with the cold start. Without that it just cranks until the starter begins to slow down.

I've replaced the O rings at the pump, but have now noticed that there is another one at the fuel filter end, so I'll see about replacing that one as well. As I'm doing all this on my own, I can't spin the motor while standing in front of the engine, so I can't actually see whether there are any bubbles in the fuel pipes. Also, all the fuel pipes have some black plastic cladding round them, so I wouldn't be able to see any bubbles anyway without breaking the cladding away.
 
Then the air ingress issue is probably the fuel filter O rings, hopefully..

You can do this single handed. Turn the key to position 2 and it stays cranking, until it starts or otherwise cuts out.
One of the only good things about a poorly designed fuel system..
 
Just to add ... set your sights a bit further for the air ingress issue, if it's not the engine bay area O rings:
1. Check the rubber pipe from the steel fuel pipe to the fuel sender.
2. On the 210 320cdi, there is also a 'well hidden' fuel return heat exchanger (like a FPHE) in front of the near side wheel arch, a return but worth a look, though..
 
a111r,

My 220cdi also has the hidden fuel cooler for the fuel going back to the tank. That's what I found when I took the plastic cover off, expecting to find an electric pump and canister type fuel filter. I was most disappointed to find just a cooler instead.

Meanwhile, this morning I've taken the fuel rail off and undone all the miriad cable ties that hold all wiring tightly together. I've also checked the resistance on each glow plug by using my ohmeter at the controller end of the wires. The plugs with the blue and black, and purple and black wires are showing 1 ohm. The plug with the red and black wire is showing 2 ohms. The plug with the yellow and black wire is off the scale. So I guess that one isn't working.

As I want the engine to start so that I can use the car over the winter, when I find out which plug has the yellow and black wire, I'll disconnect it and leave the cable disconnected till next spring. The controller will hopefully not burn out if one plug isn't there, but if there's any likelihood of that happening then I'll see about buying a new plug, and sitting it in a safe place somewhere on the engine, where it can be plugged in and heat up without causing any problems. That way the controller will still see a glow plug working even though it's not in the cylinder.

I know it's a kludge to do this, but I don't want to burn out an expensive item like a controller if I can avoid it, and having only 3 plugs working should still get the engine to start.

When the weather warms up I'll see about getting the dead plug out of the engine, but till then I'll keep soaking it with plusgas or something similar (not WD40) to try and make sure it comes out without breaking.
 
By the way, does anyone know the make and OE part no. for the glow plugs for the 611.961 engine?
 

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