Fuel pump relay

[Phil J]

I am about to start to get the bits together to wire up my Emerald controlled fuel injection system, Emerald in their wiring diagram show a normal four terminal relay used as a power switch controlled from the ECU. No problem I can see with that but, casually browsing Ebay, I noticed that there are numerous fuel pump relays with more than four terminals.

As I understand it the Emerald ECU only powers the fuel pump relay when the ignition is turned on and it has a signal from the crank sensor telling it that the engine is at least turning over so cuts the fuel when the engine stops or ignition is turned off.

My question is what extras do these multi terminal fuel pump relays do and would any of their extra functions be of use to me?

[Dave Eastwood (Gadgetman) - Club Chairman]

In the past, before the prevalence of multiple ecu systems, controlling all the different aspects of a car's control etc, and able to talk to each other over systems like Can Bus, some manufacturers incorporated "smart" type control systems by using combinations of traditional relays to route and reroute electrical signals to achieve a sort of switching logic, depending on the state of different inputs.

Others used special customised relays. For instance, some American manufacturers (and possibly others), only have the fuel pump relay energised by the ignition key while cranking, the rest of the time, its controlled by a secondary trigger, like an oil pressure switch, for example.

In other set up's, the same relay used for the fuel pump, may switch secondary contacts to trigger another vehicle system. Without knowing what you were looking at, it's hard to do much more than speculate.

Personally, I'd follow the keep it simple mantra. Add an extra function because you have a genuine need, not just because a device is capable of it! In the case of relays, especially ones that could leave you stranded if they failed, like fuel pump relays. Stick with the standard type that's available everywhere and that the AA/RAC man etc is likely to have on the van, in an emeregency, rather than something unique to a certain model of car, that has to be ordered in.

[Phil J]

Thank you for you reply, it is exactly what I was speculating it would be but I didn't want to miss something obvious or important later on.

I am a great believer in K.I.S.S. so it will be a normal relay.