Citroen XM Forum

Yes, rather a lot. Does suggest air getting in there, or fuel leaking back to tank.

Assuming the filter/priming unit is the normal Purflux one (vertical aluminium filter container, with priming button on top), worth taking the unit out of the car, and stripping (and cleaning) the filter head. There are two non-return valves in the head IIRC, meant to stop fuel going back to the tank. Also a small in-line internal sintered brass filter on the output side.

When taking bits out, ensure you make a sketch of what went where, and which direction it was pointing in!

Pump diaphragm is available as a repair item (from Purflux agents/motor factors).
Check/renew the large O-ring seal on the filter bowl (also available as a spare), and make sure its seating groove is spotlessly clean.

Might you have an engine-block fuel heater, some of which are known to go leaky/porous and let in air. By-pass it if necessary.

The usual short length of transparent pipe between filter unit and pump will show up any air-in-fuel.

russ92xmsed wrote:24 hours later and it took 6 pumps of the filter head primer untill it was solid. Which to me is too much????

6 pumps is a lot, i take it she started faultlessly after priming?

D

Mmmm, it's my thoughts too. It is too much.
No I didn't start it, but i am going to see what it has done tomorrow and then start it if it needs further priming. I want to see it if looses pressure overnight.

The purflux filter is actually new. The whole lot I got last year, or year before last. So why it would have gone pop I don't know. That's why I swapped this newish one with the old purflux filter the car came with to iliminate a leaky head.

The fuel heater has been bypassed Chris, so I doubt it is that, unless the job was done badly.

I expect it could be the pipe joins on the bulk head. One thought....

Probably no help at all, but I fitted a new Purflux filter unit complete to ours about a year ago (leaky diaphragm on old one), and then suffered really bad air-in-fuel. When I looked at the new unit closely, I found that there was a machining fault in the large annular groove that holds the big O-ring seal . . . there was a lump of unmachined metal in the groove, and no amount of bowl tightening would seal it. (Swapped back to old head, and new everythingelse.)

Thing is Chris, I used this filter on my other Xm with no issues at all. And swapping over these two on the mandarin has had no real effect. So I doubt it is the filter head.
Changing the paper fuel filter did improve things a bit, but that was last year I did that.

I finally have some time this weekend, so I will investigate all the pipes and check the fuel tank pipes, also the filter head seal. I think I will get some clear hose and fit it too.

Hi Russ

On mine I still had fuel leaking back to the tank overnight even after having bypassed the fuel heater. As I used transparent hose (PVC I think), I could see little bubbles travelling upwards. Little I mean pin-head sized. While, with the fuel heater in-line, the hoses where practically emptying of fuel with engine off. With engine running, it was plenty of large bubbles travelling upwards. As the starting up was not perfect even with the fuel heater bypassed, I decided to replace all hoses -they are 20 years old after all, how much can rubber last. So I now have transparent hose from the pump inlet, back to the metal pipes coming up next to the manifold. Solidly full fuel hoses now at all times, and not the tiniest of bubbles visible. Start up is instant even at -5C (and that's on 3 glow plugs!), and a hesitation I was getting at around 1800rpm has completely gone. Still have to do the fuel return ones, but you need to remove the inlet manifold to get there.

Hi George,

What sort of transparent hose did you choose to survive the high underbonnet temperatures?

That's very interesting Jorgy. Thanks for that suggestion. I have sort of come to the same conclusions about that too.
Right I will do that as a matter of course anyway and then I at least know it's not the pipes.

I have found a diesel place Chris that sells clear braded fuel hose for a stupidly cheap price per meter.
Just need to check sizes as I think there is 10mm and possibly 8mm.

Hi Chris and Russ

As it was meant to be temporary (for observing bubbles) I used the cheapest ebay PVC transparent (but braided), like this one: http://www.ebay.co.uk/itm/PVC-BRAIDED-C ... 3184wt_897

Still, it's been a year now, and all is fine. I heard fuel will melt PVC within a month etc, but nothing has happened. The ones I bought were explicitely advertised "for fuel", so maybe this makes a difference. There are no signs of any sort of degradation of the material.

One thing I observed is PVC may not be as elastic as black rubber hose, so the more you tighten, the more it just gives in. At the start I thought this would be a source of trouble soon, but again, all good. Just check all is tight after a few first runs. Being paranoid, I used 2 clips at every end, and of different types too (jubilee + another one).

Yes, the big supply hoses are 10mm and the smaller one returning fuel to tank is 8mm or so. The 4 or 5 little ones returning fuel between injectors under the manifold may be 6mm or so -I've bought various diameters not to be stuck when I'm in the area.

Be careful that some sellers advertise a hose as "10mm" while actually it's not metric gauge and you'll find it's more like 9.5mm when it comes to your hands.

My main concern was that the plastic hose might actually soften in the engine bay heat, to the point it might become dangerous. Good to know it doesn't.