Fuel supply problem - W203 220 cdi

[nujon]

PROBLEM - Fuel is not transferring from the n/s to the o/s portion of the fuel tank - so the car runs out of fuel with the guage showing 1/2 full. Problem started 4 months ago after changing fuel filter and putting injector cleaner in the tank. I still use the car daily but take care to keep the tank above 1/2

With a full tank of fuel, at rpm of ~ 2000 and above, air bubbles can be seen in the feed pipe from the filter to the lift pump - but non below 2000 rpm. With a lesser amount of fuel in the tank (1/2 to 3/4 full) air can be seen in this pipe even at tickover. In addition, intercepting the fuel return to the tank n/s at 1000 rpm and above reveals air / fuel slugs.

I suspect the air is responsible for the problem - i.e. the air-laden return will not initate the required venturi suction effect within the fuel transfer eductor in the tank n/s (I suspect air in the fuel supply will also result in the rail regulator restricting the tank return flow as it attempts to maintain rail pressure)

I have so far replaced the lift pump, rail regulator and pressure sensor, fuel filter and all the rubber and plastic fuel pipework between the tank and the HP pump. I presume the HP pump is ok as with any fuel in the tank o/s, the engine starts readily and runs normally

I am inclined to think that the source of the air ingress might be the o/s swirl pot due to some internal failure (eg separation of welded seal)

Been on with this for months now - can any experts suggest a way forward please?

 

[television]

Sorry that your post has been missed this is a known fault and I can look it up in the morning

 

[turbopete]

i used to get air in my fuel in my 210 (different set up, i know) but various diesel specialists said it was normal.

i seem to think there was a problem with the 203 having a fuel pump in the tank, to transfer the fuel from the n/s to the o/s section of the tank which was prone to failure IIRC

 

[S.Speed]

I had a Rover 75 once and it too adopted the so called "Saddle" fuel tank.
On the Rover forums there was loads of issues with the in tank pump..
I always thought it a crappy design that should have had an external balancing pipe and just 1 external fuel pump..
Sorry to digress a bit but it is the same sort of set up.

 

[teddycatkin]

You actually owned a "Rover"--oh dear!- I am very dissapointed in you Simon.

 

[Steve@Avantgarde]

The fault is most likely within your high pressure pump. This fault is getting increasingly common i'm finding, I have had this fault on 6 cars in the last 2 months.

There is a plunger valve inside the pump which jams open and returns all its fuel that is leaked off back to the left side of the tank, supply is drawn from the right hand side. If this valve jams then it will, as you are finding, eventually run the right side dry and then non start!!

You can get the HPP overhauled for about £200 or a recon one is around £300+vat.

 

[nujon]

Don't recognise the 'plunger valve' Steve talks about - the CN7 pump has three spring-return pistons (one per pump cylinder) driven up on their compression strokes by the cam on the pump drive shaft - and a spring-loaded N/R valve on the fuel inlet (from the lift pump). All fuel returning from the engine (i.e. via the rail regulator valve + injector leak-off manifold) is routed to the n/s of the fuel tank - the flowrate of this return should be sufficient to induce suction at the in-tank 'spray pump' (eductor) and so transfer fuel to the tank o/s - in my case, the actual flowrate is inadequate and air-laden for reasons I have yet to discover

 

[Steve@Avantgarde]

Nujon, I have to be honest, im not familiar with the internals of the HPP, I never strip them down to refurb them, I always send them to DTM in Bristol who are specialists in this arena. The "plunger valve" is what they call it over the phone to me, that maybe a slang term for something. All I know is after an overhaul the engine runs with no issues!

I diagnose the HPP being at fault for much the same reasons for the fault you describe looking at the actual values of the tanks and seeing one is full and one is empty. That can only be down to the HPP being at fault as fuel is being drawn to the engine by the tank pump when it has fuel there and then rail pressure is sufficent to run the engine.

Would you most likely see some air bubbles because the right side of the tank is near emty and is sucking up part fuel part air?

 

[nujon]

Thanks for the reply Steve - I'm going to take the plunge and get the CN7 refurbished (I've exhausted just about every other option). You raise a good point re. air ingress when the o/s tank level gets low - this could be the 'bath plug' vortex affect (and even occur at higher tank levels when the rpm and hence fuel line suction is high?) Also since posting, I've found a number of references to the presence of some air bubbles in diesel fuel feed lines at higher rpm - most report that they don't know where they come from but that they don't seem to cause any proglem (in contrast of course to gross in-leakage due, say, to a failed O ring). I have wondered if such bubbles could be vapour caused by nucleate boiling on the filter medium - but then the vapour pressure of diesel is so low that I tell myself that's unlikely

 

[nujon]

SOLVED after 4 months thanks to advice from Steve@ AvantgardeAutomotive - cheers Steve !

 

[Steve@Avantgarde]

Nujon,

No problem and a pleasure, glad you got it sorted!!

Seeing quite a few of these at the moment.

 

[dieselman]

Nice fix.
To add a bit more info, the bubbles develop as a result of the fuel being drawn by use of a venturi.
If the chamber becomes low the venturi will draw aerated fuel as a result of cavitation.

 

[or.invernizzi]

Hi Nujon. Sorry, but I have the same problem with my CDI 270 W203. The technical guys said that I need to change the rear pump and auxiliary pump inside the tank.
Could you explain me what was the solution for your case please?

 

[Silver_Star]

Hi Nujon. Sorry, but I have the same problem with my CDI 270 W203. The technical guys said that I need to change the rear pump and auxiliary pump inside the tank.
Could you explain me what was the solution for your case please?

From reading the entire thread, I should imagine he either refurbed or replaced the high pressure pump on the front of the block.

 

[MBW203]

Air Bubbles w203

I have some problems, air bubbles in fuel circuit.

I put an auxiliary tank for tests, just behind the fuel filter, no air bubbles, but, when i start the engine requests 6-7 seconds ignition time to start.

If a put again the fuel tank entry to the fuel filter, again Air bubbles.

I have seen what Steve said, and i filled up the fuel tank.
When the fuel tank is full, at:
a) at 900 rpm engine, There are very few air bubbles in the fuel circuit.
b) at 2000 rpm engine, i have few bubbles in the fuel circuit.
c) at 2500 rpm i have bubbles in the fuel circuit.
As far, i replaced the fuel filter. What should i do? To replace high pressure pump or the fuel tank is causing the air bubbles ?

 

[television]

Is this not the O rings on the pipes the should be replaced.

 

[robmalden]

I had exactly this problem with my 2000 C220CDI, it "died" on the motorway with half a tank of fuel. We had it recovered to our local garage and there was a lot of headscratching when the tank was found to have one side empty & fuel in the other. The garage asked Mercedes but their offered solution did not seem to make sense & wasn't cheap. Then I found this forum, we had the main fuel pump overhauled and the car has been fine ever since.

 

[television]

I had exactly this problem with my 2000 C220CDI, it "died" on the motorway with half a tank of fuel. We had it recovered to our local garage and there was a lot of headscratching when the tank was found to have one side empty & fuel in the other. The garage asked Mercedes but their offered solution did not seem to make sense & wasn't cheap. Then I found this forum, we had the main fuel pump overhauled and the car has been fine ever since.

Hello Rob and welcome, and thank you.

 

[ampwhu]

You actually owned a "Rover"--oh dear!- I am very dissapointed in you Simon.

I've owned a few. I started with a P6 in the early 90s. cracking power from the rumbling V8 engine.

then I went through the whole range and ended with a 75 around 5 years ago. can honestly say that the only problem in all that time was a blown head gasket on the 75. (K-series). my own fault as I ignored the leaking cooling system.

I then purchased my 1st Mercedes. no way back now...........