W124 Fuel Filter

[MB250TD]

My 1995 W124 E300 diesel (606 engine) failed to start. The starter turned over, but the car would not fire. Lots of cranking (2 batteries worth) eventaully got her to fire up and I suspect fuel starvation was the problem. On starting, diesel leaked from the top of the fuel filter from under the engine stop knob. I cleaned this up, and ensured kob was fully turned to open. The car ran perfectly over 2 days and 700 miles; started next day fine, then later that day, the problem above repeated itself. Again, it took all the power of the battery to crank it, and a fuel leak followed. I checked the fuel filter and it was full of diesel. Can anyone advise - is the problem leaking o ring seals or likele to be something else? Thanks in advance.
Regards
John

 

[Number_Cruncher]

The stop tap shouldn't leak - you need a new one.

Don't be tempted to replace the tap with a cheaper bolt from a W210.

 

[Dave Lewis]

Sounds like you might be getting air in the fuel pipes. The o-rings on the flexible plastic pipes from the lift pump to the filter get hard with age, and the pipes get hard too, and air is pulled in. Have a look for any bubbles in these pipes. The lift pump itself can wear and suck air in.

 

[230K]

The stop tap shouldn't leak - you need a new one.

Don't be tempted to replace the tap with a cheaper bolt from a W210.

What is your reason for not buying the ordinary bolt?? Is it because you cannot stop the engine if the stopper fails?

230K

 

[Number_Cruncher]

>>Is it because you cannot stop the engine if the stopper fails?

Yes, it's there for a reason. Unlike virtually all other modern engines I know of, the diesels in W123s and W124s rely on the vacuum system working properly to enable the engine to stop. Vacuum must be applied to the shut off valve to stop the engine rather than the other way round. On non-multivalve engines, the pump is accessible enough to have a manual stop lever as well as the vacuum shut-off. OM60x engines have the pump hidden under the manifold, so, there's no access to a lever.

OM60x engines in W210s are OK, because there is the electrical stop solenoid on the side of the pump which fails safe - i.e., it stops the engine.

It's the lack of a failsafe engine stop that makes it necessary to have a backup method of stopping the engine - especially in a runaway situation (which is thankfully rare).

 

[230K]

HI

Yeh i had thought of that but the "STOP" valve isn't exactly lightening fast. Frome memory the proper bolt is £20 or was it £40 can't remember and i thought if it was really needed you could pull a hose or slaken the filter........



Oh and i don't have one but a neighbour has and he bought the cheap bolt, if it was mine i am not sure which one i would have went for.

230K

 

[Number_Cruncher]

>>you could pull a hose or slaken the filter........

I think that you would struggle to do that unless you had some tools handy.

The stop tap is a bit like a fire extinguisher - 99.9% of the time everything will go just fine whether it's there or not, but, when you do need it....

One of the cruel things is that one of the jobs most likelly to precipitate a runaway is the replacement of the vacuum shut off valve - if the new valve doesn't engage the lever in the IP properly, the engine can runaway, and can't be stopped from the key.

 

[SilverSaloon]

the proper 124 stop bolt is £65 last time i checked (about 6 months ago)

the 210 version (just a bolt) is £3 odd.

i had the 210 version in my estate for about 4 months before i cheekily swapped it over with the 124 saloon i sold

my view with using the 210 version was that if all failed, and the engine didnt stop, i could just unscrew the fuel filter or pull one of the plastic pipes out and let the fuel run into a bottle or onto the floor/whatever in an emergency.

you can also remove and dismantle the 124 stop bolt and repair it. there is a thread somewhere at www.mercedesshop.com forums but unfortunatly i cant find it on a quick search - but its there somewhere and contains pics

you could of course, just require the 2 new rubber o-rings on the bolt - you will get these with a genuine MB fuel filter. always replace them.

failing that, see this thread for all the info you need on fuel leaks on your 606 engine:

http://www.mbclub.co.uk/forums/showthread.php?t=49844

the last posts on that thread has all the part number details required to fix all the common fuel leaks

 

[MB250TD]

Thanks all, and especially Silver Saloon for the very useful link. Last night the car started fine after sitting in the garage for 2 days. There was no sign of any leaks, and no air bubbles in the hoses.
However I am concerned that the problem may occur again. The only place fuel leaks were visible before was below the shut off valve (ie on the stem above the nut, but below the plastic knob with the arrow and word stop).
I am hoping that by replacing the o rings that come with a new filter, all will be well. Am I wrong here? Is it more likley that the shut off valve itself is faulty as NC suggests? Can this be serviced in any way? I am nervous at this stage about disturbing the whole system, and ending up replacing every hose and o ring as described chasing leaks that I may be creating!
As far as I can tell, my problem is a fuel leak out on top of the fuel filter, rather than air being sucked in via the hoses or connections, but I suppose one can lead to another!
Thanks
John

 

[Number_Cruncher]

>>I am nervous at this stage about disturbing the whole system, and ending up replacing every hose and o ring as described chasing leaks that I may be creating!

You shouldn't end up needing to change hoses, but, if you change all the O rings in one go (they aren't expensive), then, you can forget about it, and enjoy your car.

I know that sometimes it sounds like extreme advice, but, in my experience, it's best to plan to do the job properly, and then do it properly, and do it only once. If you start doing piecemeal repairs, you'll end up doing them again and again.

The 2 seals which come with a new filter would result in leaks lower down, between the hex and the filter head.

I think the stop valve can be dismantled and the seals within replaced. The sizes for the O rings aren't published anywhere - you might need to take the dismantled parts to a bearing & seal stockist, to match them the replacements up. If you do this, please post up the seal sizes. If possible, obtain viton seals.

 

[MB250TD]

Thanks Number Cruncher; I think I will follow your advice and replace all the O ring seals - I would rather know that it is all done properly. The hoses look yellow, but I cannot see any splits or wear, and they do not feel brittle; the connections look in good condition. The major decision will be whether I need to obtain a new shut off valve - I will report back when I have replaced the O ring seals and removed and stripped down the existing valve.
Thanks
John

 

[230K]

>>

One of the cruel things is that one of the jobs most likelly to precipitate a runaway is the replacement of the vacuum shut off valve - if the new valve doesn't engage the lever in the IP properly, the engine can runaway, and can't be stopped from the key.

Believe me i have been there with a 603, thankfully no horror stories to report but i did worry before the initial start up.

Thanks,

230K

 

[MB250TD]

Update: W124 fuel filter

I checked the car again tonight. On examining the fuel filter, I noticed that (1) the hose to the prefilter had air in it, but that (2) there was no diesel fuel around the shut off valve (ie it was clean and dry). The car started first time, and once running, (1) all hoses were air free, but (2) diesel was dribbling from a hole half way up the shaft of the shut valve. Can anyone tell me how fuel is reaching this hole, and is this normally some sort of breather hole?
Thanks for any further information on this.
John

 

[MB250TD]

Today I removed the shut off valve, and gave it a thorough clean, before replacing with a new fuel filter (topped up with diesel) and 2 new O rings. The upper (larger) O ring was dirty, and the piston in the valve looked contaminated too. I took the opportunity to remove the pre filter and clean this too (although it looked pretty clean - I only run on diesel and not veg oil!). On reassembly, the car started immediately, and ran without any diesel leakage. The shut off valve stops the engine when turned, so all looks OK. I will leave the car overnight, and check again tomorrow, but so far it looks as though cleaning the shut off valve has worked. I have not disassembled the tap (I understand that there may be a 3rd O ring in there, but some very tiny alan keys would be needed I think, and anyway, cleaning accessible parts seems to have stopped the leak). I have on order all of the new fuel hoses (about £26 + Vat), and so will probably do these as a precautionary measure - mine are all original and after 13 years, I think they deserve replacing before a problem occurs! If all is well over the next few days, then I will cancel the shut off valve (which is on pre-order at £55 + vat). Thanks for the guidance Number Cruncher and others - really useful advice.

 

[rjgodbey]

Does your engine have the plastic clip type connector on the center fuel line from the fuel filter to the injection pump? When I replaced this fuel line I was dismayed that the parts illustration at the dealer showed that it had been modified to use a banjo bolt at the connection to the IP. I couldn't believe that a bolt was going to thread into the IP where no bolt had previously been used. To my shock and awe, the IP DID have internal threads and DID accept the banjo bolt. I didn't believe the dealer/parts supplier until I took that fuel line off and looked with the help of a mirror and a flashlight...they were right and I was wrong. Turns out their technicians didn't believe it either until I showed them my now banjo bolted, air free fuel line!

 

[Uberwagon]

Just as an addition on this, if your engine does start to run away, then just shut the door and walk away, don't attempt to stop it.

Dave!

 

[MB250TD]

Yes Rjgodbey, the illustration does show this fitting and it is what I have got.
It is part 107 in:
http://www.detali.ru/cat/oem_mb2.as...GM=717.433&CT=M&cat=19T&SID=07&SGR=120&SGN=04.
John

 

[SilverSaloon]

yes the last post of the thead i linked to earlier details this:

http://www.mbclub.co.uk/forums/showpost.php?p=680905&postcount=125