: Master 2.5dci air in fuel


trampintransit
9th June 2010, 02:45 PM
My '04 Master 2'5DCi is picking up air in the diesel supply from the tank. question is this....can the air be being introduced by a common point between the return and the supply in the tank. I understand there (is there?) a low pressure pump in the tank. could the fault be that the pump mixes fuel from the return ( thereby including air, if the leak is between the injectors and the tank on the return side) or is the return isolated from the supply completely at the tank end. In which case does the pump become the main suspect? last thing i want to do is drop the blasted tank only to finf the leak is up front somewhere. I cant see a any obvious leaks on the injector returns.

madnoel10
9th June 2010, 05:16 PM
I doubt very much if there is a primary pump in the fuel tank. But check anyway. You should be able to hear it run for a few seconds when the ignition is switched on.
The most common area for air ingestion is usually on the injector fuel return pipes so it may be worth checking that aspect first.:)

trampintransit
9th June 2010, 08:53 PM
Yeah, I was suspect too, but have seen a number of references to a 'low pressure pump' in the tank!
I've got a manual coming in CD form so we'll see what that reveals.
Thing is, if air is bleeding into the return, how is that finding its way into the up supply from the tank? There must be some point in the tank where the return and supply meet for that to happen. I assumed any air in the return would simply vent into the tank void space??

trampintransit
10th June 2010, 10:28 AM
OK..have now come to the conclusion that the rate of rising air bubble in the line from the tank is minimal. It doesn't explain the large bubble that collects quickly at the clear tube going into the filter housing from the priming pump ( I've changed the filter and seals) suggesting the the bulk of the air is coming up from the injection pump. If the injector returns are leaking that air presumably is in the pump and finds it's way up through the pump and the line supplying fuel to the pump and therefore up into the filter...does that sound possible?

Ralph
10th June 2010, 10:52 AM
Lots of DCi's seem to have some air in the pipes
unless it's causing problems leave it alone you may
never stop it.
I suspect the air is normal and comes from the injectors via the leak back pipes.

trampintransit
10th June 2010, 11:10 AM
oh I'd be happy to ignore it,:d thing is it's brought the van to a stop a couple of times, and prevented it starting once:crazy:. I now have to give the filter a quick bleed before starting at the start of the day. It worries me that running it with air going through the pump will cause cavitation and damage. thanks tho for telling me about a little air in the up line being normal......but i still think i've got a problem that needs fixed. if it is coming from the returns, the plastic pipes look ok, can it be seal or whatever in the top of the injector? what about the 'clickfit' connector where the return line goes to the pump..its that a known weakness?

Ralph
10th June 2010, 11:53 AM
Sometimes a bit of grease or Vaseline round the connections
will seal them temporary and allow you to track down
a air leak, I don't think it will have a pump in the tank
as it as a primer under the bonnet, so the injection pump
is pulling the fuel through the pipes so any slight leak
will allow air in, fuel wont leak out could be worth having
a look if any of the pipes could have been damaged by
a stone or such chucked up from the road, and it could be
worth taking the fuel cap off then seeing if the bubbles
stop as that will lower the vacuum in the tank if you
have a breather blocked,
On mine a dci 1.5 there's a very slight trail of bubbles that
come from the return from the injection pump but the
leak off from the injectors join at the pump end and are
a black pipe I think the air is from the injectors on mine
I was getting some air in the feed line but a couple of
cable ties round the ends of the primer ball cured that,
on older injectors when they got worn they would allow
excessive air back through the leak offs I don't know
if this holds true on the electronic ones on the DCi but that's
an expensive last resort.

madnoel10
10th June 2010, 01:30 PM
oh I'd be happy to ignore it,:d thing is it's brought the van to a stop a couple of times, and prevented it starting once:crazy:. I now have to give the filter a quick bleed before starting at the start of the day. It worries me that running it with air going through the pump will cause cavitation and damage. thanks tho for telling me about a little air in the up line being normal......but i still think i've got a problem that needs fixed. if it is coming from the returns, the plastic pipes look ok, can it be seal or whatever in the top of the injector? what about the 'clickfit' connector where the return line goes to the pump..its that a known weakness?

The click-fit connectors on top of the injectors are a known problem area on many diesel engines and not just Renaults.:)

trampintransit
10th June 2010, 07:42 PM
I think I've cracked it. After much mucking about with bits of clear hose, couplers and jubilee clips, it seems that by bypassing the filter altogether has mad the bubbles dissapear.....so far!
I fitted a new filter and seals last week so there is possibly a crack or wear in the filter housing, or my fav theory, its the snap fit connector on the 'in' side on the filter. Since I replaced the filter' out' to pump line with clear hose i could see bubbles rushing down it at tick over. but not appearing in the clear plastic bit of hose between the priming bulb and the filter 'in', so it had to be the filter housing. Temporarily I've just put clear hose between the priming bulb out straight to the pump in, with a big plastic filter in the middle. seems ok so far, no bubbles are appearing at the new clear section at the priming bulb output. made a bloody mess of the drive though!
thanks all for your input.

trampintransit
15th November 2010, 06:18 PM
just FYI...several months later, and having installed a generic 'bloody great big metal diesel filter' from the motor factors. And everything is fine. never seen another bubble since. I'd thoroughly recommend anybody who is having rough running to look for air in the supply and junk the rubbish plastic filter housing/pushfit hose setup that's under the bonnet. Big metal filter, some hose and a handful of jubilee clips...way to go!