Hello, I hope the following assists you.
Although you changed the fuel filter the most common cause of air ingress into the fuel lines on Transit is the fuel filter housing, normally the connectors where the pipes fit. Try by passing the filter and see if the air is still evident, also run the return straight to the tank rather than through the filter this way you can determine if the air is getting in the feed or return, if it gets into the return it goes into the feed via the fuel filter.
Make sure the injector return pipes are OK and there are no signs of a leak. It is possible for air to get in via the fuel pick up in the tank so again you need to confirm if the air is getting in on the feed or return.
Once you've confirmed if it's the feed or return allowing air in this makes it much easier to pinpoint.
I hope this helps, let me know if I can assist further and I'll answer as soon as I can.
hello sean.. i,ve already tried bypassing the filter housing with both the feed and return and you can clearly see the air coming through the feed pipe...there is no leaks from leak off pipes or anywhere else that i or a few other mechanics have seen.. thanks neil
if there is excessive air in the pipe from the fuel tank to the filter then this would suggest a leak in the connector at the tank pick up or a problem with the pick up itself. As I said previously this depends on if the air is getting into the return then going back through the filter. As you bypassed the filter this eliminates this, if there is air in the pipe between the tank and filter with the return going straight to the tank again this would point to a concern with the pick up or pipe.
Let me know if I can assist further.