w209 2002 CLK270 Delivery / Primer Pump? Failure

[MackScania]

Hi All!

I've managed to get myself into a bit of a pickle and would appreciate some help and advice if anyone is able!

The cars been in my possession for about 7 months now and It's never really managed to get to operating temperature and I've suspected the likely culprit is the thermostat. So I decided yesterday afternoon I would go get myself a new thermostat and attempt to fit it myself.

Upon removing the cover and locating the install location it then became clear I had to battle with some fuel lines. During installation, I've managed to break one of them (of course). It was almost impossible to see where the pipe had actually broken from. Rather than waste anymore time I enlisted the help of my favorite mechanic who diagnosed the issue straight away as he's had the same problem with his wifes CLK. I can't remember exactly the name of the pipe that was broke but I believe it was more of a bleeder.

Anyway, had to wait until today to get the part from a Mercedes main dealer in Glasgow and after £40 for the plastic pipe, it was installed and she started with no issue. She literally ran for about 30 minutes+ at idle while up on the ramp (mechanic managed to lose a screwdriver in the engine bay) and then she simply gave up. They suspected air in the system and they just decided to keep trying her every now and then with the battery on charge. Still nothing.

After litrielly an hour they went back to check the seals weren't letting air in. Long story short, he's now discovered that the pump (delivery pump?) under the rear passenger seat isn't pumping any fuel to the front (removed main feed and pipe was bone dry - cranked it and no action from the pump).

It's been a bit rough at idle for a good while and he suspects it hasn't been working but because the system has been primed the pump at the front was sufficient to keep it going until I managed to break the pipe !!!

We tested and we're getting power to the relay but no power is actually getting to the pump. We've replaced the relay and still nothing getting to the pump.

Does anyone have any experience of this sort of issue? Does anyone know if there might be a fuel cutoff switch fitted to the car?

It's a 2002 CLK270 CDI.

Many thanks

We'll be back tomorrow spending more of my Christmas dosh trying to revive her! I don't even know if the thermostat has solved my original issue!

 

[Westheath]

I think you will find there's no electric fuel pump on the early engine, later ones perhaps.
Look at the front of the engine find the high pressure pump
and above it should be the fuel feed pump from the tank (29).
Part number A6110900350

 

[MackScania]

It's got something like this in the rear passenger side under the seat which they told me was a fuel pump :S!

 

[Westheath]

That's the fuel gauge sender unit, the electric pumps on the other side when fitted.

But I suspect you have dual fuel sender units in the tank only.

https://www.ebay.co.uk/itm/MERCEDES...d=172359125772&_trksid=p2047675.c100011.m1850

 

[Uncle Benz]

Have you checked there is fuel in the tank? I had an SL55 recovered to me the other day that had mysteriously stopped. The AA man was adamant it was pump failure. Turned out the sender was stuck on half full.

 

[MackScania]

Checked today buy putting 2 gallons in and then manually running the sender unit with external power. Got the fuel to the high preasure pump. Started no problem. Ran like a treat as always. Took her a 10 mile run to check that the original thermostat issue was resolved (Yes it was) went back to garage. After dealing with that, drove off and was just pulling onto the M8 and she died. No life. Recovered back to the garage to be looked at again tomorrow.

The fact the pump runs on external power is reasuring... Just where the wiring issue might be is the next mystery!

Thanks for your help, will keep you posted.

 

[MackScania]

The car is still off the road. 8 weeks and hasn't turned a wheel, new fuel lines, two fuel pumps and still nothing. Anyone got any ideas what else it could be. If it's primed up using a primer ball (courtesy of an old pug) she will run for 10 minutes then the diesel runs back to the tank.

 

[LostKiwi]

It must have an air leak somewhere.

 

[MackScania]

That's what the mechanic is thinking also. But I'm sure he's almost replaced every part of the fuel system. He's going to have another bash at it tomorrow. I'm pretty demented without it at this stage. Thanks for your help.

 

[mersum1es]

What exactly is your fuel system like, do you have that aux pump too in front of the engine (part 29 above), is your hp pump type 5 or 8? Have you filled your tank near to brim, and still the same?

 

[MackScania]

As far as I know and from what I've picked up, I only have the one pump and its the high pressure pump. Turns out there is no pump in the rear. The tanks about 3/4s full and there are no obvious leaks. My HP pump looks like 5 above. Fuel filters been replaced along with all plastic/rubber lines. Metal pipes have been inspected and "look" ok.

 

[mersum1es]

Do you see air bubbles in clear pipes?

 

[Westheath]

Check there's fuel in both sides of the fuel tank.

Could be saddle tank syndrome.

 

[MackScania]

I did see air bubbles in the clear pipes after the pipe was replaced in December. I don't know what it is like now post pump change. I suspect it to be the same since the problem persists.

 

[mersum1es]

Sounds like saddle tank syndrome

If 3/4 full should be not a problem

 

[mersum1es]

I did see air bubbles in the clear pipes after the pipe was replaced in December. I don't know what it is like now post pump change. I suspect it to be the same since the problem persists.

Check o-ring seal of pressure regulator valve too (back of the rail)... not common culprit but reported few times

edit: fuel filter on its own housing in this model? Check cap is tight, no crack on housing...

 

[Westheath]

I've seen saddle tank syndrome at reported levels of 1/4 1/2 and 3/4

If the senders screwed levels can be wrong, the venturi might be blocked but usually its the HPFP return valve stuck.

 

[Uncle Benz]

Have you carried out an injector leak off test?

 

[MackScania]

As far as I'm aware they haven't I'll give the mechanic the info above and see were it leads. I'll keep you posted. Thanks!

 

[Taffy7hfa]

I did see air bubbles in the clear pipes after the pipe was replaced in December. I don't know what it is like now post pump change. I suspect it to be the same since the problem persists.

Sounds like you already have the answer....
The fuel lines from the low pressure pump (directly above the HP Pump) to the tank are drawing in air somewhere, its a fairly common fault but can be hard to trace as it may be intermittent.
In order to protect the HP pump the ECU will shut the engine off without warning if fuel supply to the HP pump is interrupted or weak.