K-Jet Fuel Delivery

I tested my fuel pump delivery on a 1.8 Gti K-Jet as per Haynes manual. Disconnected the return line after the fuel distributor, linked the fuel pump relay terminals and measured the amount of fuel in 30 seconds. I was only getting 700ml in 30 secs with the pump drawing 7.5A, Haynes says my screwed terminal pump should deliver 900ml minimum in 30 secs. So I tried the test on the supply line before the fuel filter and distributor and it was a huge difference (700ml in 16 secs, @ 4A so nearly double the flow and half the current). At this point I thought it must be the fuel filter, I've since replaced the fuel filter, retested to find similar if not slightly worse results of 650ml in 30 secs @ 7.5A. Any ideas anyone?? Any advice would be appreciated.

Sounds like your pump is knackered or there is an additional restriction in fuel circuit between the tank and bay, perhaps a line has been kinked underneath?

The metering head has a pressure regulator in it, essentially a restriction, which causes pressure to build up as long as the pump has enough umph to flow the fuel.

So your findings are spot on, with the restriction (pressure regulator) the pump has to work harder hence the increased current consumption.

You really need to get a pressure gauge to measure the system (and control) pressures to see if the pump is managing to get up to the correct pressure.

I would still say your pump is on the way out though.

Is this a cabby or tin top ?

If it is a later cabby, post 84 I think, then there will also be a second pump in the tank called a lift pump - this pump may of failed or failing.

Thanks for the response!
It is an '86 cabby and does indeed have a lift pump, I checked the pump and its strainer ages ago but not while doing the delivery tests. Does anybody know what delivery to expect from the lift pump when testing separately? I'm currently sourcing bits to make a pressure tester so hopefully that may shine a bit more light on it. I've read about mesh strainers on the inlet of the pump, would mine have this as it has a lift pump in the tank with a strainer attached?

Not sure on what a lift pump should deliver. To be honest I have them run fine off the car in the past and then fail in the car under load. They only cost about £25 new so best to get a new one if in doubt.
They are only fitted because VW consolidated to one common tank for carb and injection.

If the lift pump has been failing then you need to check the fuse box and the fuel pump relay, because as you found as the main pump fails to deliver it draws greater and greater current trying to do so, sometimes it is enough to melt the solder on the relay. I have seen it where this eventually caused the fuse board pins to corrode away.

Ok, thanks for the tip, I assume all will become clear after some pressure tests.

It will help. But I did find once that even with a failing lift pump the main pump kept the pressure up all be it with some very aerated fuel. It manifested itself as a loss of power and fuel starvation. So it is a combination of flow and pressure that is required.

Where did you get your new lift pump from? I couldn't see them on the GSF website. As you say, for around £25 I may as well replace it.

Pretty sure it was Crazy Quiffs

Fuel pressures checked today, here are the results:
System pressure with engine running and test valve closed = 5.3Bar
Cold pressure with AAV & WUR unplugged with test valve open = 1.3 Bar
Warm pressure with engine up to temp and AAV & WUR plugged back in with test valve open = 3.5 Bar
After the test I left the test rig connected, pressure was 2.9 Bar and didn't drop in 20mins.

I thought I'd test the lift pump flow so disconnected it and ran it in a jug, it produced approx 1000ml in 30secs, when I closed the valve to test the pressure it would produce I noticed it was spraying from the pump, I thought it might be leaking from the short piece of hose on the pump but it turns out there's a tiny hole in the top of the lift pump (see photo). Does anybody know if this is supposed to be there, I assume it is to relieve the air out of it??

I had a low delivery volume on mine which I traced to voltage drop to the pump. You can either check the voltage drop with a multimeter or run the pump directly from the battery (fused) and a temporary ground.
The bently manual says the lift pump should deliver 300ml in 10 seconds - so seems good. I would bet the hole in the lift pump is a pressure release as the pump is not designed to create high pressure.
gav