Air In The Fuel

[colin]

Maybe all is not going too well with my new XM.

The last few mornings I have had to spend about 30mins bleeding air out of the fuel lines before it will start. Once this is done it goes well all day, only to do the same again, and there's lots of air to bleed!

It seems pretty obvious that I have a very small air leak in the fuel line, most likely between the filter and the tank somewhere back under the chassis.

Has anyone else experienced this and is there a typical rub/bend point where it goes?

Or do I have to just start at the beginning (its raining again)

[noz]

Hi Colin,

The two favourite locations on the 2.5 are:

A leaky diaphragm on the primer pump. Not sure if you can buy a spare.

A leak in the rubber feed hose just where it joins the steel tube on the bulkhead behind the inlet manifold. It will be difficult to spot because its on the suction side so no fuel will be evident. Feel teh end of the rubber tube with your fingers and you'll be able to feel the wet surfaces and your fingers will smell of diesel.

Please let us know how you get on.

Cheers

noz

[colin]

Noz,

Is the primer pump submersed in the fuel tank, if so I dont have a primer pump (or I didnt yesterday)

Cheers

[noz]

Hi Colin,

No, the primer pump is located on the top of the fuel filter which is bolted to the battery tray. The little black knob on the top is the plunger. Just push it down repeatedly until it goes almost solid. There's also a black plastic knurled thumbscrew at the top of the filter towards the front of the car which is an air bleed. Just slacken by 1/4 of a turn as you pump.

I now have to ask the question though, when you say that you had to bleed for 30 mins, how were you bleeding and what was providing the pressure to bleed with? Were you cranking the engine for 30 min?

Cheers

noz

[colin]

No, I was using the priming pump but didnt know the name of it (too much time working on my own).

I have just stuck my hand down the back of the engine and there is definately no leak at the union between the rubber and metal. I will have a think on this since its raining again!!

I may just go and replace every pipe I can see.

The junction on the fuel supply line about 6" on the tank side of the fuel filter...is that supplying a bit of fuel-preheat via the radiator?

Cheers

[noz]

Wow, sounds like you have the last 2.5 in the country to have its fuel pre-heater bypassed. I didn't think there were any left.

There is a pre-heater block bolted to the side of the cylinder head exposed to the passing hot water at the rear. The block is diecast and is notorious for being porous. All other 2.5's have the pre-heater bypassed.

Just locate the two tubes taking the fuel into the bowels below the water pump and back out again. Either undo the jubilees which hold the tubes onto the heater or cut them. Then install a short length of 10mm copper pipe in the open tube ends and a couple of jubilees to hold the tubes on. Bob's your Auntie.

Cheers

noz

[colin]

Noz,
You saved my life, I could have spent a lot of time looking for the air leak if I didnt know about the problem with the heat exchanger.

I have bypassed it and its all very different now. No more air in the fuel and it starts and runs perfectly.

Thanks very much

Colin

[noz]

Glad to be of service. Thats what were here for after all. Glad to hear you got it sorted.

Happy XMing

cheers

noz