Another RRC not firing (fuel problem)

[paulmmc]

Hi,
I've just replaced my 3.5 V8 onto a new chassis and did the basic wiring to get the engine running, it is turning, the fuel pump is pumping and there is a spark at the plugs but not firing at all.
I am learning as I go so really don't know what else to check, at the moment no fuel is coming back through the fuel return pipes, but when i disconnect the fuel feed line it is spraying petrol, so looks like fuel flow is stopping when it reached the engine. What could this be?
Any suggestions welcomed.

I have said all along I'll do whatever i can myself but if i need to call in the experts then so be it. Does anyone know of a good mobile mechanic who would work in the Enfield Area (north London)? But obviously i would rather sort it myself for monetary reasons but also I want to know how to do it.

Cheers, Paul

[bogie]

By the sound ,its an efi which means something electrical on the efi is not connected or blowen,so stopping the fuel from entering the system and returning!

[Rossko]

Are you convinced you have the fuel flow and return pipes the right way around?

The easy wire to leave off is the EFI rpm sensing wire to coil -ve, it won't fire without that.

[clbarclay]

Have you checked that fuel isn't entering the cylinders?
Easiest check of this is unburnt fuel (white mist) coming out the exhaust when crancked.

Assuming the pipes are plumbed the right way round, the fuel pump supplies fuel direct to a common rail feeding all 9 injectors. A fuel pressure regulator is on the end of the fuel rail and if pressure in the fuel rail rises too high (pump supplying more fuel that the injectors are using) then the excess is returned to the tank.

If the pump is working properly then the fuel must be going somewhere.


Also are you certain the pump is getting fuel?
I've had quite a bit of fun recently with crud in a fuel tank getting disturbed and blocking a fuel system.

[paulmmc]

I double checked today and the fuel pipes are definately the right way round, i disconnected the supply pipe just before it connects to the engine and fuel was spraying out while the ignition was cranking so i am happy the pump at least is working. Is it possible for a fuel blockage to occur somehwere in the fuel rail and if so what is the best way of checking and curing it?
Just to convince myself i had wired it up properly i sprayed some of that 'Easy Start' aerosol into the air inlet while cranking the engine and it did fire briefly, so it is definately a fuel problem.
As far as i can tell everyhting running from the ECU is hooked up to where it should be (or at least where i think it should be).

Any more tips greatly appreciated.

Cheers, Paul

[Range Rover Blues]

So you have the spark in roughly the right place, the fuel pressure to the injector rail and a good battery.

Check the resistor pack for the injectors (3.5 flapper systems use 5 volt injectors).


If the EFi is working right then the fuel pump should run for one second when you turn on the ignition then go off, it only starts again when the ECU sees the ignition coil signal to say the engine is turning.

You could check the fuel system by bypassing the pump relay next to the ECU so that the pump runs continuously.

[paulmmc]

The fuel pump is running full time while the ignition is turned on, so that definately isn't right then! But now i am confused, could it be that the fuel pump is working (as i can see it spraying petrol) but it is not working at full pressure? But surely even with low pressure petrol supply it should fire a bit?

Cheers

[Rossko]

could it be that the fuel pump is working (as i can see it spraying petrol) but it is not working at full pressure?

That's what it sounds like.  If pressure is too low to return from the regulator, there really won't be much getting through the injectors either.   Sure it's an EFI pump?  Sludge in tank, pump and/or filter?

Continuous pump run may be because the flapper is stuck open a bit.  In the normal course of events, with the ignition on, you should be able to poke the flap to make the pump run and release it to make it stop.

[paulmmc]

It is definately an EFI pump as it came out of the same donor car as the engine.
Where would i find the 'flapper'? The only one i can think of is in the air intake?

[Rossko]

Where would i find the 'flapper'? The only one i can think of is in the air intake?

That's the one, if you have the 3.5 type of EFI system.   The flapper carries a set of contacts for the fuel pump, so that the pump won't run unless the engine is turning (drawing air).
You seem to have continuous pump run which suggests something wrong there

BUT

with a running pump you should have fuel spilling back in the fuel return line, or pressure is nowhere near high enough to inject.  Focus on that for now.   A blockage in the rail is really unlikely, a gummed-up regulator is going to prevent fuel return (this would lead to overpressure, but I doubt prevent firing).  My guess is pump is too pooped to make enough pressure, or possibly burnt pump relay isn't delivering enough voltage to drive it fully, or scabby earth.

[paulmmc]

Right, I've had some minor success this weekend, I found that the fuel hose in the inboard fuel tank was a bit shagged and so was leaking fuel when under pressure, which was why the fuel was coming out of the pump but not returning down the return lines, so a new section of hose and it's flowing back down the return line properly.
While we're on the topic, there was some kind of coupler between the actual pump and the hose within the fuel pump unit, what does it do because it does not make for a tight fit to withstand the high pressure required? Is it necessary?
So now the pump runs when the key is truned, fuel return down the return pipe, there is a spark in the cylinders (as it runs on 'Easy start' aerosol) but injectors are not injecting.
I'm fairly convinced it's an ECU/sensor related item so I think I'm going to call in an auto electrician as my brains turning to mush looking at all the wirse coming out of the ECU!!

Thanks for all your help.

Paul

[paulmmc]

I got it going this weekend!!!!
It turned out to tbe the fuel injection relay (the red Pektron one) under the drivers seat near the ECU. I replaced it with a substitue and its all working well. I had replaced all the other relays as they were common types but fuel injection one had to be a special Pektron one, which i picked up at the LRO show in Peterborough.