Replacing clear plastic fuel pipes and o rings

Ad777

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Hi there have just got 6 new pipes and o rings from dealer for my 99 c250 td. Can anyone give some advice as to how to approach this..the old pipes are rock hard, maybe heat gently with hairdryer?! Any advice appreciated, Adam
 
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Ad777

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Nobody got any advice? Am doing this tomorrow. Cheers Adam
 

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Wear gloves and pull on them hard , but be aware they will all of a sudden pop off so you need to be careful you do not smash the back of your hands.
New ones just push them on but lube the o rings with a bit of fuel to make them go in easier.
Refit an old one to get a feel of it going back in to get an idea of the force needed , its not much but the new ones will need a little bit more push.
On my 97 w210 om606 the fuel would keep running out from the tank when any fuel hoses were removed including injector leak off pipes, so may pay you to clamp off the fuel to engine and return lines where the metal lines exit from under the car and join up with the rubber lines front passenger side back at bulkhead... 10mm id in and 8mm id return respectively.
 
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Ad777

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Thanks Doug, exactly what I was looking for. Greatly appreciated, Adam
 

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Thanks Doug, exactly what I was looking for. Greatly appreciated, Adam

You may have problems starting the engine after replacing the pipes. If you do, feel free to give me a call at work on 01707 395999 and I’ll help you out all I can.

Phillip.
 

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Use a small screwdriver to prize the pipe up out of fitting.
 
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Ad777

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Thank you both. I will let you know how it goes, and will take you up on that Philip, if required! Appreciated, Adam
 

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As above, plus the pipes are brittle and may break as you pull. No matter, they are scrap. Make sure you clean the connections before installing the new pipes. As also said, the motor may take ages to start as the air gets purged from the new pipes. Be prepared for a long starting procedure - in small doses - and have a battery charger handy in case of need.
 
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Ad777

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That's it done..it wasn't too bad! All came off quite easily. The gaskets were shot in the inlet manifold so replaced them too. Started after a couple of minutes so quite lucky i think! Still air bubbles going through pipes so not holding my breath..we will see how she starts over the next couple of days! I will update. Thank you very much for offers of help and input. Cheers Adam
 

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If the filter set up is the same as the om606 engined cars there will be a small pre filter that has a small tab and a 10mm bolt holding the filter in place, I always would just fit two of the small o rings to the pre filter and this would stop air getting in.

Pre filter is highest point in fuel system that air can get into pipes and it will let fuel drain back to tank overnight, you will read lots of posts where car is parked facing downhill and starts but will not start when parked uphill and this pipe join is normally the problem.

Being its a c250 I expect you are aware of saddle tanks and to keep tank level always over 1/3 minimum ?.
Laser pointer or temperature gun shone on pipes will show bubbles more easily.
 
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Ad777

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Thanks Doug. That is exactly the issue. Always keep the car nearly full, but still have to reverse onto a couple of bricks to be sure of starting in the morning! Can you tell me where about in the engine bay the pre filter is likely to be..assuming it's in a similar place to yours.
I can quite clearly see the bubbles in at least 2 pipes. Appreciated, Adam
 

Doug1234

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https://forums.mercedesclub.org.uk/index.php?threads/c250-td-fuel-filter-housing.135628/


The last picture in the above link, pre filter is circled and marked as ‘input’
You can see the 10mm bolt that holds the tab down that keeps the pre filter in place.

All I would do with mine was replace the o ring as normal and then just fit another ( same size) and just roll it above the one that is fitted correctly and that would keep the air out.
In an ideal world just the one o ring works ok but the tab that holds down the pre filter is soft metal and over the years the tabs bend upwards and do not hold it down as tight but you can slightly bend them back with pliers.

The 10mm bolt just needs nipping up , going to hard on it just bends the tabs again.
 
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Ad777

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That makes perfect sense. I found it this morning..it had new pipe and o ring fitted yesterday, but I will slide another o ring on to be sure, and straighten the bracket which looks slightly bent. It started this morning on the level so looking hopeful...touch wood. Veering off topic..my alarm has been going off intermittently today. I have read a few threads saying it is located behind plastic passenger side wheel arch, and I can just disconnect it. Any chance you could confirm this! Cheers, Adam
 
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Ad777

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https://forums.mercedesclub.org.uk/index.php?threads/c250-td-fuel-filter-housing.135628/


The last picture in the above link, pre filter is circled and marked as ‘input’
You can see the 10mm bolt that holds the tab down that keeps the pre filter in place.

All I would do with mine was replace the o ring as normal and then just fit another ( same size) and just roll it above the one that is fitted correctly and that would keep the air out.
In an ideal world just the one o ring works ok but the tab that holds down the pre filter is soft metal and over the years the tabs bend upwards and do not hold it down as tight but you can slightly bend them back with pliers.

The 10mm bolt just needs nipping up , going to hard on it just bends the tabs again.
I have done the above, as well as all the fuel pipes and o rings..Still a pig to start in th morning unless I am pointing downhill! Is there anywhere else to look that may be letting air into the system/ fuel drain back into the tank? Advice as always appreciated! Adam
 

Doug1234

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Leak off lines between injectors replace those , fuel will run out as you remove them so have them cut to length ready to put on.
On the rear injector don't use the soft rubber cap that is often supplied in a hose set but instead cut a short length of hose and but a bolt in one end and use that.
 
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Ad777

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Thanks Doug..I have just finished reading an old post describing that very procedure! I will get on it and post back when done. Thanks again, Adam
 

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Did you change the O ring behind fuel shut off valve? D06DE3F2-E84F-429B-9A94-34DAC16A9B92.jpeg
 
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Ad777

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I did not.. where about is that located please?!
 

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Side of delivery pump.
 
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Ad777

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Thank you.
 

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