Maintaining Fule Pressure

[MickR]

Hi

Hope someone can help.

Am having trouble starting my L reg ZX Volcane 1.9 turbo diesel.

The engine runs fine when started but needs a combination of many pumps on the hand pump bulb and a heavy foot on the throttle to get it going.

It feels like I am loosing pressure from the low pressure side of the fuel system (pump it up with the squeezy bulb but the pressure drops quickly and the resitance against the hand pressure dies).

 

Can't find any leaks in the bleed off pipes from the injectors (have replaced those many times in the past) and have blanked off the fuel pipe into fuel pump and the pressure holds.

 

Do not know whether it is significant but if I take off the bleed pipe from the injectors that meets the fuel pump on the same side that the injector pipes are situated (on the same manifold as what I assume is the fuel return pipe) the fuel pumps out of there when I squeeze the hand Bulb suggesting that the pressure is being lost as the fuel is being returend to the tank, is it supposed to do that?

 

The engine has done 128K miles and the car has been the failthful family runaround for 10 years (never though I would say that about a French car) :lol: suprising us year on year with 1st time MOT passes. Hope someone more clued up than me can point me in the right direction

 

Many thanks

 

Mick

[Guest Colin Hunter]

Hi Mick.

 

Because the XUD engine doesn't have a seperate "lift" pump, the fuel injection pump draws the fuel from the tank itself. This means that the part of the system before the pump is under negative pressure (suction) when the engine is running, and any imperfection could lead to an ingress of air. This will be the cause of poor starting at the very least as the fuel system needs to be purged of air before the engine will start. This is why you are having to pump the bulb to get air free fuel to the injection pump. I would look for an air leak in the pipework between the priming bulb and the injection pump. The cover of the fuel filter is a favourite, and has been the subject of another, similar thread in the Xantia forum.

 

Because the system is "Self Bleeding" it is perfectly normal for the fuel you are pumping up with the priming bulb to find it's way back through the return lines. This is also connected to the injector leak-offs and this fuel finds its way back to the tank.

 

When you blanked off the fuel pipe to the pump and the pressure held, you were simply preventing the fuel reaching the return side. When you did this did you notice any leaks in the pipework between the bulb and the blanked off end. Any fuel leak, even minute, in this area would lead to air ingress when the engine is running, or when stationary, as fuel will leak back to the tank instead of staying in the system. Air will find a way in where diesel may not find a way out!

 

Citroen actually say not to use the accellerator when trying to start the engine as it intruduces excess fuel which cannot be burnt,"Quenching" the heater plugs and resulting in a shedload of black smoke when the engine eventually starts.

 

It may be a good idea to check out the heater plugs as well as the XUD (and any other indirect injection engine) really needs them to be in good order. My TD Xantia needed a full heat cycle even when the engine was hot!

 

Cheers Hope you get to the bottom of it! :rolleyes: