Fuel pump issues

[MatthewH5]

Hi,

I replaced the fuel pump in my Mk1 Focus 1.6L (petrol) yesterday as the old one was completely dead. It's an internal pump which sits inside the fuel tank along with the level sensor. I just replaced the pump motor itself and kept the original housing. I've not started the car for over two years but I'm trying to get it back on the road.

After replacing the fuel pump I'm still getting no fuel flowing to the rail, although I do hear it priming on ignition now. I disconnected the fuel supply and return lines from the pump housing tonight and powered it on again to eliminate any blockages between the pump and the rail, but only a slight dribble of petrol comes out of the housing. I replaced the fuel filter just before I SORN'd the car so I didn't think there would be any issues there. I've also tested the input voltage and it does supply 12V when priming.

The fuel level was very low when I changed the pump so I suspected this may have been the issue. I added another 4L of petrol tonight and retested but there's been no improvement. Is it possible that the pump is somehow air-locked due to attempting to start it dry? I've never heard of this being an issue on petrol engines but I know diesel pumps can have these problems. If not I'll have to take it all apart again tomorrow and ensure everything is seated correctly.

[stevieturbo]

What did you replace it with ?

A new pump that simply plugs in, or something else ?

Did you make any pipe connections inside the tank ?

Can you test for fuel flow close to the tank ?

[MatthewH5]

stevieturbo said:

What did you replace it with ?

A new pump that simply plugs in, or something else ?

The pump motor was a direct replacement for the original part but non-OEM. I attached the new motor to a 12V supply before fitting it and it appeared to work to correctly.

stevieturbo said:

Did you make any pipe connections inside the tank ?

No, I removed the fuel pump housing from the tank, split it open and the new pump drops in (sealed by o-rings). All of the internal fuel lines are fixed to the housing and don't need to be removed to swap the motor.

stevieturbo said:

Can you test for fuel flow close to the tank ?

Yep, I tested flow at the tank and only a tiny amount trickles out when the pump primes.

The housing did have a couple of "strainers" (mesh filters) to pre-filter the fuel before it goes into the pump. It may be possible that these have become blocked and are preventing fuel from entering the pump. I'll remove it all again tonight and try spraying some brake cleaner through them.

Thanks

[MatthewH5]

I forgot to update this thread. I did some testing on the pump while it was out of the tank. The problem turned out to be the pump outlet seals (red) on the housing. These were not holding pressure so the majority of the fuel was leaking back down into the housing after priming. I fixed these seals and it's all working correctly after putting it back together. This may be useful to other Mk1 Focus owners as the problem wasn't obvious until you see what's happening while it's out of the tank.