Joel1993 Posted November 23, 2016 Posted November 23, 2016 Hello everyone The other day I was driving. No issues then came to a roundabout and car stopped and wouldn't turn back on. Turned out the ecu power wire had come apart. Anyways soldered that back together and now my fuel pump won't turn on. I have my fuel pump on by a switch that I installed and I have never had a problem. Checking the voltage... with the positive and earth on the switch it was reading 12v however when I introduced the fuel pump wire to the switch the reading goes straight to 0v which is very strange It gets stranger.... If I take the fuel pump power wire (which I used on the switch) and put it straight to the positive battery terminal (which is in the boot) the pump starts up no issues... What could be causing this? Thankyou Quote
sayers Posted November 23, 2016 Posted November 23, 2016 your switch is dropping straight out to earth, try another switch, and make sure you are introducing the right wire from the fuel pump Quote
Stephen Posted November 23, 2016 Posted November 23, 2016 Is the switch and wiring you added suitably sized for the current drawn? Quote
Joel1993 Posted November 23, 2016 Author Posted November 23, 2016 Yeah I had the exactly the same set up when the car worked. I have tried different switches and it's the same story haha Quote
Stephen Posted November 23, 2016 Posted November 23, 2016 Just because it worked doesn't mean it was right. Does your switch have any function other than cosmetic? Quote
Bones28 Posted November 23, 2016 Posted November 23, 2016 Maybe a relay or fuse, that's why direct to battery works. Quote 2002 Porsche C2 996 3.6 1991 Nissan 300zx TT Project 1995 Nissan 300zx TT Crashed 🥲 1997 Jaguar XK8 Scraped ☹️
Alic Posted November 23, 2016 Posted November 23, 2016 There is the small fuse box next to the drivers side firewall, you can swap the interior seats and windows fuse to the fuel pump to check if its blown. Quote
Joel1993 Posted November 23, 2016 Author Posted November 23, 2016 Just because it worked doesn't mean it was right. Does your switch have any function other than cosmetic? The reason I put it in is so it would be harder to steal if anyone wanted a free zed haha Quote
Joel1993 Posted November 23, 2016 Author Posted November 23, 2016 Maybe a relay or fuse, that's why direct to battery works. It's wouldn't make a difference because it goes straight to the battery through a switch. All I am doing is losing the switch and it works - - - Updated - - - There is the small fuse box next to the drivers side firewall, you can swap the interior seats and windows fuse to the fuel pump to check if its blown. Looking at those fuses they all look good but it's worth a check mate :) Quote
Alic Posted November 23, 2016 Posted November 23, 2016 It's wouldn't make a difference because it goes straight to the battery through a switch. All I am doing is losing the switch and it works - - - Updated - - - Looking at those fuses they all look good but it's worth a check mate :) So straight to the battery it works, but from the battery through a switch doesn't work. Isn't it a given to just get a heavier duty switch or just bypass the switch. Quote
Chrisbasildon Posted November 23, 2016 Posted November 23, 2016 When you test a supply voltage with no load present you can get a 12v reading, but as soon as you introduce a load onto the circuit the voltage will disappear if there is a poor connection somewhere. You need to check where you took your 12v+ supply from to supply your switch. that could be faulty on the supply side of the switch or your negative supply could be poor with a Load on the circuit. It can be beneficial to use the old fashioned 12v incandescent test lamp as this will introduce a load on a circuit and give better indication of a good supply, modern day led test lamps draw such a low current that they can light up showing voltage when in fact there isn't Test meters can show voltage too but when a load is imposed it will disappear. Quote
Joel1993 Posted November 23, 2016 Author Posted November 23, 2016 So straight to the battery it works, but from the battery through a switch doesn't work. Isn't it a given to just get a heavier duty switch or just bypass the switch. The switch is 20amps which is plenty. And if I put it straight to the battery then it would be on constant. The other reason I did it was my fuel pump ecu broke so I had to bypass it. I have a aem fuel pump so I wasn't bothered about the constant voltage as I knew it could take it. Quote
Joel1993 Posted November 23, 2016 Author Posted November 23, 2016 When you test a supply voltage with no load present you can get a 12v reading, but as soon as you introduce a load onto the circuit the voltage will disappear if there is a poor connection somewhere. You need to check where you took your 12v+ supply from to supply your switch. that could be faulty on the supply side of the switch or your negative supply could be poor with a Load on the circuit. It can be beneficial to use the old fashioned 12v incandescent test lamp as this will introduce a load on a circuit and give better indication of a good supply, modern day led test lamps draw such a low current that they can light up showing voltage when in fact there isn't Test meters can show voltage too but when a load is imposed it will disappear. Thank you mate I will try the supply line. Quote
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