Fuel pump wiring

[dommorello]

Hi guys,

Anyone have a wiring schematic that details the fuel pump?
All the diagrams we have shoe the fuel pump red wire coming back to connection ( no. 103 in Haynes book but different no. others) but then does show other side of this connection and what fuse provides the fuel pump power.
Very confused at this point and any assistance would be appreciated
Thanks

[Neil-yaj396]

Was an electric pump standard in Australia? Not sure the UK members will be much help, the pumps were mechanical here right up to the VX/ie.

[lukasdeopalenica]

As far as I know electric pumps were installed as a standard in injected or volumex models only. Below you can find a schematic diagram with drawn provision for the pump (84), this suggests that late models may have installations prepared for pump use.
On injected models fuel pump is fed through an additional relay set and fuse, located on a RHS McPherson strut, and then via a gray wire.

[dommorello]

No electrical pump was not standard but wiring lume & schematics have provision for electrical pump. Seem to have worked out that the power to pump runs via relay and switch connected to oil pressure switch. Does this sound right? Haven't tested and tracked fully as yet

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[mangocrazy]

I run an electric pump on an S2FL Spider, but my implementation is not one you'd want to copy; I just piggybacked on the power to the coil for the electric fuel pump, and it's something I've been wanting to put right for a while. Is there a spare circuit I can use for this? Also I presume any such circuit should have itsown fuse and relay? Any pointers on how to do a proper job gratefully received.

[gengis]

Hi Dommorello,

The circuit you describe would work.  Having the coil of the fuel pump relay conditioned by the oil pressure switch, means that in the event of a crash (engine stopped) the fuel pump would also stop, preventing fuel being sprayed over hot engine.

[lukasdeopalenica]

That is the way it works in VX models, on injected ones fuel pump operation is determined by an AFM flap tilting.

[dommorello]

We are still having issues understanding the fuel pump wiring. Any other ideas as the oil pressure theory makes sense but doesn't seem to work the pump when we Earth the oil pressure switch

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[lukasdeopalenica]

Hi,
do you mean the vx or the IE example? Only these have factory electric fuel pumps. I only know to depth operation theory of the IEs configuraton. In this case the pump is supplied and controlled by a special double relay and the pump operation is conditioned by AFM's flap position. In the case of VX version at least as far as I know there are two sensors conditioning the pump work - oil pressure switch and there is another unit - a sensor or an electrovalve but I do not really remember, but it is a kind of a troublemaker for the owners...

If you are about to install an electric pump in a carb model installing a kind of a cut off system is a good idea. Using the oil pressure swith is a good choice. This switch would supply a ground connection to a fuel pump relay. If there is no oil pressure (engine crank not rotating) the fuel pump feeding relay is not supplied with ground. When you crank the engine the oil pressure switches the ground to the relay and allows it to supply electricity to the fuel pump.

[WestonE]

If you are installing an electric pump in a carb model consider an inertia cut off switch on the earth feed to the relay you install. This will cut the fuel in a crash and immediately provide fuel when switched by the ignition so you have less time cranking before the car starts. They are widely available and fitted to most modern cars. I bought mine from Weber.

In summary you need a relay with fused permanent battery power to pin 30. Pin 85 goes to earth via the inertia switch. Pin 86 is a switched live feed from your location of choice. Pin 87 is power out to the fuel pump. I would take battery positive directly from the battery connection and have the earth direct to the body shell to minimise the chances of old wiring preventing the pump running as it should.

Eric     

[mangocrazy]

Thanks Eric. Exactly what I needed to know. I have to confess, relays are something of a mystery to me. I understand what they do (use a low level of current to switch a much bigger one), but not really how to wire one up. As a matter of interest, what would be your location of choice for the switched live feed?

If you are installing an electric pump in a carb model consider an inertia cut off switch on the earth feed to the relay you install. This will cut the fuel in a crash and immediately provide fuel when switched by the ignition so you have less time cranking before the car starts. They are widely available and fitted to most modern cars. I bought mine from Weber.

In summary you need a relay with fused permanent battery power to pin 30. Pin 85 goes to earth via the inertia switch. Pin 86 is a switched live feed from your location of choice. Pin 87 is power out to the fuel pump. I would take battery positive directly from the battery connection and have the earth direct to the body shell to minimise the chances of old wiring preventing the pump running as it should.

Eric    

[peteracs]

Hi

Old school relays are pretty straight forward, the live feed goes into a coil which creates a magnetic field. This field moves a metal actuator which mates or breaks the contacts. The thing you are looking to feed such as the lights are connected to these contacts. The coil uses a small amount of current and lows the much larger current to be switched.

This got me wondering if using solid state relays might be advantageous in this application, do the same job, but would they cope as well with the harshness of the under bonnet environment (probably) and likely poor earths/spikes etc?

Peter

[lukasdeopalenica]

The solid state relays have two main cons. First they have relatively low efficiency due to voltage drop at the semiconductor layers and second when fail they usualy keep the circuit switched on - that is actually the same effect when the conventional electromechanical relay contacts get sticked

[peteracs]

Hi Lukas

Good point about the on state resistance, not sure what values that would equate to for typical use with lights and hence the voltage loss.

I was not aware they fail shorted typically, guess it depends on the nature of the failure.

I did see that they are much more susceptible to over voltage failure than traditional ones, which again makes its use in cars (especially older ones!) less attractive I guess.

Peter