For those with XUD / XUDT that smoke in the morning.......

8304 · Unread post by **8304** » 26 Feb 2006, 10:15

hi

there have been loads of posts on here about psa diesels smoking on first start - up in the morning generaly considered to be as a result of air in the fuel line....

Ive changed all leak off pipes and all fuel pipe under the bonnet leaving the metal pipe under the car as the last suspect place for letting air in.

i changed the metal under car fuel pipe yesterday with one from citroen (£18 ) . It will be interesting to see if it is cured this morning. if it stops mine smoking - try it on yours!!

alastair

8304 · Unread post by **8304** » 01 Mar 2006, 08:39

there was a small crack in the metal pipe where it runs up the bulkhead.

the pipe has been changed now and there is a definate improvement but its not perfect.

i now suspect the fuel filter housing - or the seal in the top.

im going to fit a standard inline fuel filter like on a petrol to see if there is any improvement, bypassing the big diesel fuel filter..

ill let you know..

Unread post by **Peter.N.** » 01 Mar 2006, 09:59

Dont leave the proper filter out for to long, its essential that the pump has clean fuel. If you replace the section of pipe, or part of, between the filter and the pump, with a clear piece, you will be able to see any air bubbles. Pleased to hear that you have found some elusive leaks. I dont expect you will stop it initially smoking completely, unless the engine is in almost new condition. In this cold weather you will get incomplete combustion until the combustion chambers warm up, which may take a few seconds to a minute

jeremy · Unread post by **jeremy** » 01 Mar 2006, 15:39

If you have the black plastic fuel filter remember there is a heater in the bottom and this si controlled by a thermostat which is a round device in the filter body. This thermostat can leak and let air into the filter. . .

There are instructions on dealing with this problem on this board somewhere

Kowalski · Unread post by **Kowalski** » 01 Mar 2006, 17:48

jeremy wrote:If you have the black plastic fuel filter remember there is a heater in the bottom and this si controlled by a thermostat which is a round device in the filter body. This thermostat can leak and let air into the filter. . .

Thermostat?

I know that the fuel filter sits on top of the thermostat housing (i.e. the water / cooling system thermostat), I've had a filter apart but never seen a thermostat or a heater apart from the fact that the filter sits on the thermostat housing. There is a sensor in the bottom of the housing too that is there to detect water in your fuel, is there a separate fuel thermostat too?

jeremy · Unread post by **jeremy** » 01 Mar 2006, 21:26

The question of the thermostat in the filter unit came up several times towards the end of last year - and I recall someone even posted some photos . The only reference I can find now is:

http://www.frenchcarforum.co.uk/forum/v ... hp?t=17271

pugxpert · Unread post by **pugxpert** » 01 Mar 2006, 21:49

the coolant will heat the diesel and not cool it,there is a valve inside which directs fuel through heater to warm diesel when very cold ,as engine warms this closes and diverts diesel not near heater as no longer required.hdi has electric diesel heater in fuel filter and also a fuel cooler on the return.

BonceChops · Unread post by **BonceChops** » 01 Mar 2006, 22:58

The fuel cooler seems a little pointless. It will soon cool down when it travels down the fuel line and into the tank.

pugxpert · Unread post by **pugxpert** » 02 Mar 2006, 07:51

when fuel is put under extreme pressure the tempreture will rise as well,hdi runs at high pressure to a max of 1350 bar fuel pressure,unwanted fuel that is returned to the tank can reach near on 60 degrees this has to be cooled ,if you only have 10 liters of fuel in tank and no cooler by the time it has been pumped round the system a few times its going to get bloody hot

Mandrake · Unread post by **Mandrake** » 02 Mar 2006, 07:58

1350 bars ?

or 1350psi ?

1350 bars seems almost unbelievably high when you compare it to the 170 bars (2400psi) used in the hydraulic system in the suspension

Regards,
Simon

Unread post by **RichardW** » 02 Mar 2006, 08:17

1350 bar - on the first generation. Second generation is 1600 bar.

Indeed!

jeremy · Unread post by **jeremy** » 02 Mar 2006, 09:54

I confirm that the injection pressures used on HDi engines is enormous and many times that used on meachanical systems. The pressure of the mechanical systems had been increased gently over the years presumably in the interests of better atomisation and no doubt is part of the reason that black-smoking diesels are relatively uncommon except for 4 X 4's around London.

Presumably the use of electric pumps and injectors has enabled higher pressure to be used.

Kowalski · Unread post by **Kowalski** » 02 Mar 2006, 10:53

When Volkswagen was banging on about the PD system they were saying that it had a major advantage was that the pressure it used was higher than common rail systems. At the time common rail systems were only running at 20000 psi (1350 bar) where as the common rail system could run at one and a half times that pressure, i.e. 30000 psi (2000 bar). So it seems like things have moved along but the newest common rail systems only run at 24000 psi (1600 bar)!

I think that the mechanical pumps on the TD engines would inject at something like 100-200 bar. The limiting factor here would seem to be the injector pipes, when you subject them to great pressure, they stretch and expand so your not all of the pressure you produce at the pump reaches the injector. The pipes get hammered too, constantly being pressurised and depressurised so they can and do suffer from metal fatigue. PD got rid of the injector pipes and common rail got rid of the pressurisation / depressurisation and pressure loss problems on the injector pipes because the common rail is at a near constant pressure.