Fuel cut-off/inertia switches

[Sgt Pepper]

As part of the Zetec conversion the mechanical fuel pump has been replaced by a Pacet, what's the general advice on fuel cut-off switches for sprinting?

 

Am I right in thinking that these are present in most Caterhams out of the factory and that many of you disable them for sprinting as they can cut in when riding the kerbs?

 

Now, am I right in thinking that if you're on an injection system there is some sort of return pipe/valve that kicks in when the engine stops to allow fuel to return to the tank or something vaguely similar?

 

But, does anyone know what the situation is with running an electric fuel pump with carbs? For instance, in the unfortunate event of an accident does the fuel pump keep pumping until someone kills the ignition? If so, does this then not significantly increase the risk of a carb fire?

 

As you'll probably gather I'm a little confused by this, so any advice would be greatly appreciated.

 

Soon to be powered by a more modern Dagenham Boat Anchor ☹️ 😬

[CaterBram]

My x/flow had an electric fuel pump which i've reused for the zetec on carbs. with webbers you still have fuel in the chambers so an inertia switch in the fuel line would not stop the engine straight away

 

No inertia switch on mine, but would appreciate others advice if ones needed.

 

 

 

-----^{Q469 WET, 1990 Long Cockpit in Ali except for the red bits. Class 2 150 BHP Zetec. With a Dual Drive :-)CaterBram on Facebook}

 

Edited by - CaterBram Jnr on 29 Jan 2011 18:41:49

[jj48]

Hi Chris-i have heard of a system were the electric fuel pump voltage supply is cut by means of the oil pressure dropping to a certain PSI -ie if you are involved in an incident(heaven forbid). Think it was a Bosch system used on K- jetronic fuel systems in the 80's because the system pump is ignition operated and if the car was upside down the pump would still supply fuel if driver unconscious etc. Also this system was of a very high operational PSI.

Regards

Richard

 

Sussex Swede R400

[Adrian Williams]

A standard injection car has a fuel return pipe which is in constant use as the electric pump pulls fuel out of the tank, pushes it through the fuel rail and back through the return pipe. Power to the pump can be cut in anumber of ways:

1: Turning off the ignition.

2: Inertia switch cutting out (possibly over a kerb as stated).

3: ECU will cut power to the pump if the engine has stopped (no reading from the crank sensor).

 

So, in the event of an accident with a disabled inertia switch the fuel pump will only continue to run if the engine is still running.

 

As to advice with your installation, if the pump is not controlled via the ECU and you do not wish to fit an inertia switch the pump will continue to run after an accident until either you of the marshals turn it off. If the fuel lines are intact after said accident there is no problem, however if the fuel lines have been severed it's a differnt storry and one you wouldn't wish to find yourself in.

 

For what it's worth my car does not have an inertia switch at all.

 

 

Adrian

[Sgt Pepper]

Thanks Richard & Adrian,

 

Primarily I was concerned about what would happen if the engine stopped and the pump kept pumping petrol into the carbs, but I understand that once the float chamber is full the needle valve shuts off the fuel supply and it is of no consequence if the pump keeps pumping. Is this not the same as when idling? I guess the problem is if you are upside down as the needle valve won't shut off the fuel into the float chamber.

 

Adrian, you raise an interesting thought re broken fuel lines though . Something I'd not considered.

 

So I need to find out if my ECU can control the fuel pump. I have a feeling that it doesn't. If that is the case what are my options?

 

Oil pressure switch as Richard suggests or any other ideas?

 

Soon to be powered by a more modern Dagenham Boat Anchor ☹️ 😬

[CaterBram]

I think this is what they were thinking about

 

I'm on megajolt and does not look like I can control the fuel pump as the minimum RPM enable level for the outputs is above cranking RPM.

 

-----^{Q469 WET, 1990 Long Cockpit in Ali except for the red bits. Class 2 150 BHP Zetec. With a Dual Drive :-)CaterBram on Facebook}

[Sgt Pepper]

CBJ

 

Soon to be powered by a more modern Dagenham Boat Anchor ☹️ 😬

[bluenose]

The Omex 200 does not control the fuel pump. Many other ECUs do and hence you can put a relay between the ECU and the fuel pump to cut it. The oil pressure switch sounds like a good way to go.

 

Nick

 

Lava Orange Caterham Blackbird

 

[Offspring]

For my 2p:

 

Carb pumps are usually external to the tank and for higher flow/pressure units will deliver approximately 25gal/Hour and produce about 7 psi + have to be regulated to 4psi to the float chamber, where as a tank immersed roller cell fuel injection pump can deliver approximately 65gal/hour @ 30psi and is designed to circulate fuel but maintain a constant pressure at the fuel rail.

 

In the event of an accident where the car is upside down the external pump will struggle to lift petrol out of a tank, where the injection system without cut-off protection will continue to work. There is also the increased chance that a broken injection pumped fuel feed will spray a mist of fuel and greatly increase the risk of ignition not to mention the amount of fuel that will escape.

 

In addition to this, in the case of my carb (Twin 40's,Facet Red Top/Filter King) setup, when it looses pressure it makes the most horrendous rattling noise on the rear bulkhead, giving me fore warning that either I have run out of fuel 😔 or my fuel line has been damaged.

 

Al