matt-k 0 Posted February 22, 2008 As above really ive wired my facet pump to a live and earthed it to the body so it comes on with the ignition. Is this ok or do i need to wire the pump using the original pumps wireing at the tank so the relays on the system. What does the relay do exactly?? Thank You. Matt. Share this post Link to post Share on other sites
Anthony 1,000 Posted February 22, 2008 I wouldn't suggest wiring it to be live with ignition, as in the event of an big accident it's a major fire risk. Run it using the original relay that is only live when the engine is running. Share this post Link to post Share on other sites
Tom Fenton 1,526 Posted February 22, 2008 The other way to do this safely is to get a fuel pump inertia cut-off switch, and wire it inline with the pump. In the event of a big shunt the switch is tripped and cuts the fuel pump supply. These are easily available on lots of modern cars in the scrapyard, I believe some Fords (Mondeo?) are a good source, they are located behind the kick panel next to the drivers feet IIRC. Share this post Link to post Share on other sites
matt-k 0 Posted February 22, 2008 So using the relay is for safety reasons. Thanks guys. Share this post Link to post Share on other sites
DrSarty 90 1 Cars Posted February 22, 2008 So using the relay is for safety reasons. Thanks guys. Yes. The Mi16 ECU and many others, including my Volvo, make the fuel pump operate for around half a second when you turn on the key. The 'tachy' relay on the standard 205s does the same job. It just primes the line, but requires an ignition signal for it to keep pumping. As a result, in a prang and when the engine stops, the signal to the ECU/tachy relay stops and hence stops the fuel pump continually working. These inertia switches do exactly the same in the event of a prang in so much as they trip as a result of force and cut-out the power to the pump. The only issue is that if you turn only the ignition on without the 'tachy relay effect', then your pump will keep running. Share this post Link to post Share on other sites
pugrallye 0 Posted February 22, 2008 Normally, its advisable to wire in a fuel pump relay, for two reasons, your not running 2.5mm wire everywhere, which is expensive and heavy and you can also turn the system on and off via a multitude of sources. Its usually good policy to wire relay in via a oil pressure switch... engine off pump doesnt run, one way valves will ensure the line pretty much remains primed. Most cars running post jetronic injection will have a fuel pump controlled by a relay (nothing special) via the engine ECU so will self prime whether it be an ignition cycle or drivers door opening, older versions of management will have a timer controlled relay, which is expensive and prone to failure, which will pulse the fuel pump according to demand Share this post Link to post Share on other sites
