Hi
A friend of mine has just saved a XJ6 from the scrap heap , the problem is it does not want to start.
It was described as having bad fuel and needing a fuel pump. New fuel pump , filter and plugs fitted and now the car fires and dies .
My question concerns the fuel system
How does the return fuel system work , on this car it appears to return to a junction block on the pump outlet to filter line , is there some sort of "valve " in this junction .
How can the fuel rail can bleed itself of excessive air if it just returns to the filter.

 

Unused fuel returns to the tanks via a return pipe that is routed at the very front of the cylinder head, thru the fuel cooler, downward and along the underbody. The piping splits left-right so that fuel can be returned to the same tank is was drawn from, via solenoid valves located in the rear wheel wells. When the left tank is in use, the left return valve is opened and the right is closed, and vice versa.

The return fuel is sent directly to the tank in use. If you open the gas cap and look inside the tank you can just see the returning fuel entering the tank from a small metal pipe. If you have the flapper door in the filler neck for (unleaded fuel nozzles) just hold it open with a screwdriver. A small flashlight helps as well.

The gizmo you are referring to at the pump outlet is the air bleed. As I recall it works within the tank venting system. It is separate from the return system.

The symptom you describe might be caused by a number of things. My first thought is the fuel pump does not stay running. The fuel pump circuit has two branches: start and run. The 'start' branch operates the pump whenever the key is in the 'start' position. When the key is released the 'run' branch comes into play, operated by a switch in the AIR flow meter. These two branches are controlled by a diode pack. Electrically downstream of the diode pack is the fuel pump relay....which actually powers-up the pump itself.

More reading on the subject:

Fuel Pump Circuit Checklist

Cheers
DD

 

The cold start injector can supply sufficient fuel to get the engine to fire, but the EFI system relies on a pulse from the ignition system. This is provided by a wire off the coil back to the EFI control box in the trunk. Without this pulse the injectors won't fire. BTW, they are fired all together, twice per engine revolution.

 

You can easily test if the second part of the fuel pump circuit works. Remove the air cleaner. Now with the key turned to the on position, lightly open the door/flap inside air sensor. If the circuit is working properly, you can hear the fuel pump turn on and stay running until you allow the flap to close again.

The return system works off the fuel regulator. The excess pressure is piped back into the tank, so a properly working pressure regulator will keep the rail at the necessary pressure so long as the fuel pump keeps up.

 

Simpler is to put it into gear then try to start.The start inhibitor on the gearbox will prevent starting, but the pump will start.

 

Thank you all who responded , a lot of useful information .
Worked on the car yesterday and am now sure the pump runs as it is meant too. The injectors have a pulse , so have removed injectors for a clean.
Will up date when the injectors go back in.

Andy