'99 C250 TD W202 with air in fuel line - won't start

[purps]

Hello all, not had to post before due to the wealth of information available, but now I could really do with some advice please.

Our C250 TD isn't starting properly, due to air in the fuel line. I assume it's probably a leak somewhere from other posts I'v read, but it's not obvious to me where or how. I am very confused as what the various pipes are all doing!

Please see picture attached. We can JUST start the car with the nose pointing down hill, and after a few cranks to get rid of the air, it starts. Once we get it going, the car runs just fine. When you switch off the engine, you can see tiny bubbles moving in the direction indicated in the photo (there are two arrows, one has light reflecting off it!). The pipe with the larger arrow has slightly larger bubbles.

Does this give any clues as to where the problem is? Definitely a seal, or could it be a valve? Or the lift pump?

Cheers,
Matt.

 

[neilrr]

O rings leaking?

Are your lines opaque or is your fuel that murky? What fuel are you running it on?

 

[purps]

Thanks for the reply!

Nope they are see-through and look quite clean to me! Bad photo perhaps.

Just running it on bog-standard diesel - whilst I am planning to run it on biodiesel at some point, it's not had any in it yet.

Cheers,
Matt.

 

[Dieselman]

Have the engine idling then rev sharply. Wherever you see the bubbles first is the leak point.

 

[purps]

Great suggestion, I will try my best but I find it very difficult to see with the vibrations. Will give it a go though.

I've just bought a new fuel filter, seeing as it needs doing anyway. Are these the 'o' rings you are referring to neilrr?

What/where are the other 'o' rings to check out?

I was going to replace the pre-filter as well, but my local autofactors doesn't carry it - where can I get one of those from? Any 'o' rings there? Worth doing?

Cheers for the help guys,
Matt.

 

[neilrr]

Search the forum for 'o rings' & you'll find info like - http://www.mbclub.co.uk/forums/engine/31269-fuel-leak-606-td-engine.html


Also have a look here - vegetableoildiesel.co.uk - Powered by XMB

Search for 'C250 TD O rings'.

The veg oil seems to damage the OEM ones & these boys know all about replacing them.

 

[SilverSaloon]

you can clean the pre-filter as its just a mesh filter.

buy the replacement viton o-ring kit from ebay

 

[purps]

Do I need to do anything before I start from the point of view of fuel piddling everywhere, or can I just start whipping fuel lines off?

Do I need to remove the manifold to get at all of these 'o' rings or can it be with it in place?

OK that's all good to know, no need to waste money on a new pre-filter then, as cheap as it is. And the eBay kits includes and 'o' ring for that I see.

I am somewhat torn - whilst I am cynical, the stealer recommended I get 6 all new fuel pipes for ~£60, but of course they would say that wouldn't they. I just can't see any obvious splits in these lines.

Cheers for all the advice guys,
Matt.

 

[purps]

This is the view into the top of the lift pump once I had removed the fuel line (with the pre-filter at the other end).

As you can see there seems to be a ring in the top of the lift pump (sort of looking at it end on, the black thing) - what is that?

Cheers,
Matt

 

[Dieselman]

Don't know as your photo is of a glow-plug and the fuel heater, not the lift pump.

 

[SilverSaloon]

thats the fuel heater, not the lift pump.

is that ring an old perished oring? if its rubber try to pull it out with thin-nosed plyers. that could well be a reason things are not sealing. there isnt any "loose" rubber things in there so if there is its an alien part! you should be able to see the little thermostat inside and nothing else.

once all the orings are replaced, you'll be able to trace any airleaks if there are still any by identifying the pipe where the bubbles 1st appear... the airleak will be in the oring at the start of that pipe. the main thick black rubber pipes ends go brittle with age too so dont discount these aswell.

try the orings 1st. its unlikely but possible the clear pipes have hairline cracks in due to age but doubful. orings usually are the cause and brittle main black pipe that runs from the metal pipe that runs under the car into the fuel heater

 

[Olivier]

It might be the SOV Oring leaking? Did you change it?
As Silver Saloon said, change the Oring and it might help?
I had troubles with the pre-filter leaking air, the car was trully hard to start in the morning, no matter how big, small, new or old orings I was putting in.
I just bypassed it and voila, no more fuel going bak to the tank
Apparently there is no tank strainer on the 250? I might be wrong there tho, but if you have one, take it out and clean it as if its clogged ant teeny air leaks that you have will show as the LP will try to suck anything it can.
Olivier

 

[purps]

Thanks for all the advice guys, it's been really helpful.

Sorry, it's my first diesel, didn't even know it had a fuel heater. Anyway, once I got the manifold off, it became obvious (I think) that the "ring" was normal/supposed to be there.

Replaced all the 'o' rings, including pre-filter, car ran great for a week, brilliant.

Then today, bam, same problem again. Air in the same place. I'll check the main thick black pipe, but are there any other suggestions?

Cheers,
Matt.

 

[ozzy1000]

Matt, did you ever get the bottom of this problem?? my C250td is doing exactly the same thing. I have a feeling mine might be the black pipe as when I poke it more bubbles appear....

all the best,

Owain

 

[guydewdney]

main fuel line from hard line on the bulkhead is a known leak point. cut back and re-clamp. also leaks around the other end - the fuel thermostat under the inlet manifold.

 

[stability]

be careful these lines can be very brittle when disconnecting !!!!!!!!!

 

[ali.shaikh22]

Hi did you replace the O'ring on the Stop solenoid too?
I had the same issue last week but after replacing the O'rings the car still wouldnt start.
I ended up spraying easy start into the manifold whilst trying to turn it over and eventually it started. Could be worth a try?

I was told in my post, once the car does start, turn it off, take the manifold off and turn it on again to get a clearer view of the fuel lines and where the bubbles are appearing. But to not rev it at all and to be very careful to ensure nothing gets into the holes.

Its been going for a week now and fingers crossed will carry on going.

Let us know how you get on

 

[hondo]

Don't get carried away with easy start your engine will become addicted to it ! Also o-rings and washers on delivery valves on top of pump are problematic on om605

 

[purps]

I hate to leave threads hanging, really sorry I have not rounded this one off. I was googling around another issue I am now having with my C250 and happened to find my own thread again and saw I hadn't replied.

Back then, it turned out to be the black plastic part, sorry, I can't remember what part it is! Had two lines going into the top and one into the bottom if I remember correct. I took the car to Merc Medic in Woking 3 times in total, and eventually that part was replaced. It has 2 circular bung looking things on the end of it if that makes sense, and it was those that were leaking.

Cheers,
Matt.

 

[purps]

Ah, shut off valve?