wr won't start, starving of fuel?

[Mark Hanman]

I don't recall the figures i got when i did all this a few years ago.
However. If you can draw fuel out at the rate of 2ltrs/30secs, does that not indicate a reasonably good supply to the pump?
The issue is delivering fuel to the metering head.

[george21]

that is what I'm thinking that all the way from pump , fuel accumulator, fuel filter i have good flow right to metering head, and just out of it on return pipe no flow or very little. is that not mean that fuel is almost blocked there( i still can start the car for few sec.) if i leave pump running for a bit longer and not accelerate on start up engine runs a bit longer as well. so what to check on metering head for blockage?

Originally Posted by Mark Hanman

I don't recall the figures i got when i did all this a few years ago.
However. If you can draw fuel out at the rate of 2ltrs/30secs, does that not indicate a reasonably good supply to the pump?
The issue is delivering fuel to the metering head.

[se97rjs]

If you have a difference in flowrate between the delivery line and the return line the fuel has to be going somewhere. A blockage will not affect the volumetric flow rate. A blockage only affects the flow velocity. You are measuring the volumetric flow rate so a blockage would not be detected by this method.

I would try and find where the fuel is going as that is likely to be the route of your problem.

[Mark Hanman]

Originally Posted by george21

is that not mean that fuel is almost blocked there( i still can start the car for few sec.)if i leave pump running for a bit longer and not accelerate on start up engine runs a bit longer as well.

At this stage, it could be a few things- the car running for a short time before stalling. The fuel flow in the return pipe is very low. The car starts, so that suggests that initially, a reasonable amount of fuel is getting into the injectors. So fuel delivery from the pump is insufficient with the engine running. With the fuel pump running, and the engine off, you are simply building up a small reserve of fuel that gets depleted very quickly once you start.

Originally Posted by george21

so what to check on metering head for blockage?

I did ask a couple of questions, to which no reply.
And Jim and Julian have put in items to check. So plenty of things to check on before really struggling for ideas.

One more. There was a lot of discussion a few years ago about a fuel strainer on the metering head.

Here is what I would check before any major work on possibly dubious fuel pipes under the rear of the car.

Is there a fuel pump relay? With the pump running all the time, either the relay has welded internally, or the relay has been replaced with a bridge.
Simple thing to check, and report back.

If there is a relay, I would remove it, bridge the Fuel pump relay contacts, see if that makes a difference. We already know the pump runs permanently when the ignition is on, so we are only changing one thing, the electrical supply to the pump. Fuel flow away from the metering head is currently 100ml/30sec with the present situation.
Has this made a difference?

just for starters.

[Mark Hanman]

Originally Posted by se97rjs

If you have a difference in flowrate between the delivery line and the return line the fuel has to be going somewhere. A blockage will not affect the volumetric flow rate. A blockage only affects the flow velocity. You are measuring the volumetric flow rate so a blockage would not be detected by this method.

I would try and find where the fuel is going as that is likely to be the route of your problem.

The flow rate is higher coming out of an unrestricted delivery line. Is the fuel pump circuit working well enough to continue the same delivery rate when the line is connected to the metering head?
I'm fairly certain that if the fuel really is being delivered at that rate continuously, and not being burnt by the engine, then there would be some sign of this.

[Mark Hanman]

a bit of background to my thinking...

I have encountered a fuel pump relay failure several times before.
The contacts had partially welded, leading to poor contact, and then seriously over heated. The relay then melted a little bit, causing misalignment of the contacts. When the relay was cold, the pump ran. But not so well. As the circuit heated up, the pump stopped because the eroded contact patch was now a very bad circuit.
XR4i. K-Jet. The circuit is a little different, but not by much.

Same car. The fuel pump failed, getting very loud. Fuel delivery was enough to keep the engine running on a light throttle, but not enough for normal performance.
Eventually, it failed to the extent that the car would stall when the throttle was opened.

A friends quattro. Fuel pump relay problem in the fuse box. The contacts in the fuse box were very loose, and the relay making poor contact. The pump would run intermittently, and so the car wouldn't run for long. Bridging the relay contacts sorted the problem temporarily. tightening the contacts in the fuse box fixed it.
The pump was fine, but with the relay making poor contact the supply to the pump was very poor. Just enough to run the pump, but nowhere near what it needed.

Knowing the state of some of the fuel lines at the back of some of these cars, I would rather eliminate some other factors before resorting to changing the filter, as you might end up with a bigger job to do.

[chezz]

I have recently encountered a similar experience i.e shutting down after 10 -15 seconds... the cause was diagnosed as a very tired 20+ year old noisy fuel pump, failing to maintain sufficient system pressure.

[george21]

I'm sorry guys i have not checked things today, that is the job for tomorrow. i will report back how the things going. i really appreciate for all the help here!!

[JimH]

Julian is correct about the reason for checking fuel flow rate at the return line. The pumps delivery rate must be checked against the restriction imposed by the pressure regulator in the metering head.

The fact that the fuel delivery is good at the supply line makes me think that the fuel filter is probably ok, and isn't creating a restriction (although it is a service item requiring regular replacement anyway).

So, the problem is either the fuel pump is too weak to provide the necessary flow against the normal restriction (pressure regulator) - due to bad pump or wiring/relay as suggested.
Or there is something wrong with the pressure regulator / metering head.

Can you check the fuel pressure in the delivery line when it's connected to the metering head in the normal way?
>6 bar = problem with metering head pressure reg
<6 bar = problem with pump/wiring/relay

If you can check the system pressure - good.
If you can't, go down the route of checking the pump & it's electrical supply as already suggested.
If you cannot find anything wrong with the pump, get a pressure gauge on and check system pressure before you go replacing the metering head (££££).

If the pump all checks out ok, the fix might be as simple as removing the pressure regulator from the metering head, cleaning it and putting it back.

[george21]

that is what I'm thinking Jim! i have spare working metering head, which i will fit tomorrow and see it how it goes. if no good I'll get a fuel gauge to check pressure on delivery pipe. it can be two things metering head or pressure accumulator. but maybe I'm wrong, will see tomorrow. i wish it still be light now....