Pre filter/piping leaking diesel

d215yq

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Hi all, just found why theres been an intermittent wet patch under my car for the last 6 months. Ive just seen the pre filter/pipework nearby has diesel on it. Im assuming that its actually the ancient pipework which is covered with fabric that is leaking but want to replace all pipes in area and prefilter to be sure to eliminate..they all look accessible so less fuss to do it all than try to find which one is leaking...so questions...

1) over last 600 mile trip from uk to toulouse car harder to cold start and very slight misfire type vibration at 3k rpm up hills, could this be the cause as its drawing in air? Also mpg down a little than expected but if its losing some diesel then fair enough.

2) ill order a new prefilter when i get back but where do i get the pipes. Could i get say 1m of a certain diameter fuel hose (which diameter?) and cut to length as needed or do i need to get individual mercedes parts. do the pipes have to have fabric protector or will any rubber fuel hose do?

3) ill fill pre filter with veg oil but when i fix it will it need a lot of cranking to fill pipes?. Also when i disconnect will it explode with pressure or is this part not under pressure at all as i think it is fed by being sucked from the tank?

4) im 400 miles from home. Assume car can be driven as has been for 6 months unless the pipe bursts completely which is unlikely?

Thanks in advance.
 

LostKiwi

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1. Yes.
2. Yes any fuel tubing of the same size will do. Fabric covering is optional.
3. Probably, No, Not sure.
4. Yes but if you can get tubing why not fix it and remove the risk?
 
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d215yq

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1. Yes.
2. Yes any fuel tubing of the same size will do. Fabric covering is optional.
3. Probably, No, Not sure.
4. Yes but if you can get tubing why not fix it and remove the risk?

Thanks, very helpful, definitely diyable then...regarding 4) not even sure what diameter it is until ive taken it apart and im struggling to think of where i could get it in spain let alone france. Id also rather do it at home chilled out with a beer not worrying about being stranded in case it doesnt have enough crank after or something breaks while doing it...also im going to replace prefilter (its 80k miles) so have to wait for that to do in one go. I assume i can reuse the jubilee clips?
 

LostKiwi

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As long as they're in good condition yes.
I personally prefer this style (in stainless) for fuel lines:
hose-clip-mini-14-mm13.jpg

For large hoses I prefer Mikalor clamps.
 

om613

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Take it to a commercial diesel place, explain the predicament, and they'll sell you the 8 or 10 mm pipe and clamps needed.
The pre-filter is not really needed, so you can eliminate this and simplify.
No exploding will happen ... the IP driven mechanical lift pump is doing the work.
 
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d215yq

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Thanks for suggestions, it already has the clamps shown and they look non corroded. Does anyone know what mm the pipe is or where i coudl find out? I know i could take some pipe off and ask for replacement but then i would have to fix it where I buy it from. I've also got some important journeys for a few weeks and little time for agro so would like to cut the pipes to length and stick them in the boot and then do it when convenient (or if it leaks a lot more).

I appreciate the pre-filter is probably not necessary but at 2 euros for a bosch one happy to keep it in there anyway, also does this diagram suggest the pipe is 8mm (measurements on the pre filter are 8.1mm?) so fit an 8mm hose?

https://www.mister-auto.es/filtro-combustible/bosch/0-450-904-077/
 
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d215yq

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Was I not meant to do it with 2/3rds full of diesel?

I disconnected pre filter and its just pouring diesel non stop. About 5L in containers and 1L on the floor whilst trying to contain it! In the end I've got it so that the pipe is wedged high and therefore no longer leaks. So can change the whole thign engine side as it's stopped leaking. But when I reattach the final pipe to the fuel line it will be leaking diesel all the time, as teh fuel hose is lower than where i've wedged the pipe, unless there's a trick to stop this?

Also although the hose i bought was the correct internal diameter it's thicker so the clips don't work so I have to wait til Monday to finish it all anyway. TBH wish I'd just stuck with the small leak....

What's the deal with starting it after? Presumably I've introduced a lot of air into the system now so maybe it will run on the fuel in the filter but then will stop running a few miles later when it hits air. Or have i misunderstood it?
 

LostKiwi

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Why will it be leaking once you reattach the pipe?
 
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d215yq

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Its not leaking because pipe attached to
Why will it be leaking once you reattach the pipe?

Well i cant reattach anything as the clips are wrong for new thicker pipe. Its stopped leaking because ive raised the height of the pipe attached to fuel line and wedged it there. So it no longer leaks and i can buy my clips and do the engine side stuff without worry.

But when i need to attach new piping to fuel line then it will be leaking. So can i stop this or just do it quickly and let it leak everywhere while changing?
 
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d215yq

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Sorry if im being dumb but i didnt expect this. I thought as filler line is higher than tank then i could catch the diesel in the pipes/prefilter and it wouldnt continuously leak...
 

LostKiwi

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Your tank is either under pressure or its siphoning. Remove the filler cap to release any pressure.
You could always clamp the flexible line to stop the flow. Wrap the jaws of whatever you use as a clamp to prevent damage to the pipe.
 

Doug1234

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It will always run out from the tank if any hose that is removed is below the level of fuel in the tank.
So if fuel tank was full and car is parked facing downhill then even an injector leak off pipe coming off will empty the tank.
Let it leak while you quickly put the hoses on it but just do it quickly and do clips up once hoses are on and then straight away start engine and hold on about 1500rpm while it bleeds any air out.
The pre filter is very handy as any crap blocks it up and engine will run rough with a lack of revs ... but you can then swap another in or run without it and carry on ... but if it wasn't there the main filter would block and you would be stranded.
 
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d215yq

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It will always run out from the tank if any hose that is removed is below the level of fuel in the tank.
So if fuel tank was full and car is parked facing downhill then even an injector leak off pipe coming off will empty the tank.
Let it leak while you quickly put the hoses on it but just do it quickly and do clips up once hoses are on and then straight away start engine and hold on about 1500rpm while it bleeds any air out.
The pre filter is very handy as any crap blocks it up and engine will run rough with a lack of revs ... but you can then swap another in or run without it and carry on ... but if it wasn't there the main filter would block and you would be stranded.

Thanks, maybe the tank is higher than i think. If id known id have done it empty. Car is not facing downhill.

Ive bought some clips and so can do all piping on engine side and then swap fuel line while leaking. As itll be my last one should be able to do it very quick by then.

Will include pre filter as i bought a new one and then see what happens when i start it and rev it.
 

Doug1234

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Its better to let it keep leaking out as you change the pre filter because otherwise you may need to crank the engine over a lot to get it running.
Remember its running out of both pipes ... the one on engine and obviously the pre filter one... the suction pump on the injector pump lets it run out as well which will drain some fuel from main filter and empty the clear pipes to and from it .
And no matter how you try the pre filter will always have an air bubble in it, its nothing to worry about its normal.
 
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d215yq

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Thanks all for replies. With the proper connectors was fine. Started it and revved and never missed once. Started immediately. Left it idling 15 minutes and all ok and theres some fuel.in pre filter (though its not full but the old one wasnt either). Was also extremely clean of smoke while cold idling, so.maybe it is running better already...

Does that mean job done and ok to drive now? And it wont suddenly stall a few km later?

I notice theres two other pipes but they must have been put on with inlet manifold in place as cant get to connectors easily. I might try those when its got less diesel in and uphill so i can take my time. Will need to wait a while to see if ive fixed leak as theres diesel evrrywhere. Lucky its not on exhaust side!!
 
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d215yq

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Forgot to add in all the excitement didnt prefill the pre filter. But as i say checked once running and it had filled itself? Is this ok?
 
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d215yq

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Done a few hundred miles and realise the car is smoother than it was before and also produces no smoke at idle even up to 3500rpm, where it used to smoke a lot more if idling just after starting/also with revs of 2000rpm. Also starts a lot better.

Just out of interest is all that because I've fixed the diesel leak/air getting into the system or is it more likely to be the new pre filter? Be good to know in case I get the symptoms again in the future...
 

Doug1234

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Mainly the pre filter change but air leaks will sap power and the pre filter blocking up will cause air to be pulled in on fuel lines.
It may seem impossible but if the fuel tank breather blocks on these old Mercs then the fuel suction pump on the injection pump will suck the fuel tank nearly flat.
 

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