Fuel Pump Wiring Experts, I need help |
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Fuel Pump Wiring Experts, I need help |
wndsnd |
May 17 2019, 07:53 PM
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#1
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You wanted a horse, but got a goat. Nobody wants a goat.... Group: Members Posts: 2,861 Joined: 12-February 12 From: North Shore, MA Member No.: 14,124 Region Association: North East States |
My fuel pump is in the front.
It is fed by the original wiring at the rear suspension point If I power the fuel pump from an auxiliary 12 volt source fed from the rear, the pump runs. That eliminates the wiring from rear to front, and the pump. If I put a meter on the pump wiring at suspension point I get a reading of hundreds of volts. How do I get Hundreds of volts from a 12 volt circuit. I am guessing a short would cause amps, not volts. I have been changing relays, and the board. I did what Dave Darling mentions and checked out the #30 at both board relays. I had constant 12 V there I changed the fuses. Car was run hard in the rain for a couple of days. I suspect water got into something but where? Relay board was covered. Everything else seems ok. Maybe it is not water. What do you guys think? It has to be somewhere between the board and the wiring at suspension point. Is there another connector between the suspension point and the board? Lots of questions..... Sorry. Thanks |
Superhawk996 |
May 18 2019, 10:29 AM
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#2
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914 Guru Group: Members Posts: 5,875 Joined: 25-August 18 From: Woods of N. Idaho Member No.: 22,428 Region Association: Galt's Gulch |
If your meter is operating correctly and you are getting voltages significantly higher than 12 volts, you are getting flyback voltages induced from somewhere.
Flyback is when the magnetic field around and inductor collapses after being turned off. Most relays have a flyback diode in them that will short this high voltage spike to ground to keep it off the supply line. Cheap relays from Radio Shack or auto parts stores often don't have proper flyback diodes. Induced Voltage = L dI/dT where L is the coil inductance and dI/dT is the instantaneous change in current. Shutting off current to a coil (or relay primary) via switch (or points) equals a very high dI/dT and high(er) voltages up (potentially to hundreds of volts) can be induced from a 12 volt source. Do you have any relays that are being opened and closed rapidly? If you have a defective ignition coil with a bad (open) secondary you can get induced voltage spikes onto the 12 volt primary line as the primary circuit is cycled by the points (mechanical or electronic) and the flyback voltage is induced on the primary line rather than being "absorbed" into the secondary. https://www.allaboutcircuits.com/textbook/d...s-and-calculus/ |
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