 Fuel Pump Wiring Experts, I need help |
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| wndsnd |
 May 18 2019, 09:46 AM
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#21
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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   |
QUOTE(wndsrfr @ May 18 2019, 07:31 AM)  QUOTE(Specracer @ May 18 2019, 01:42 AM) LONG SHOT question, is the battery fresh in your multimeter, and giving you solid correct info? (IMG:style_emoticons/default/agree.gif) I know it it not. I will change out now[i] |
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| Superhawk996 |
May 18 2019, 10:29 AM
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#22
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914 Guru Group: Members Posts: 7,499 Joined: 25-August 18 From: Woods of N. Idaho Member No.: 22,428 Region Association: Galt's Gulch 
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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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| wndsnd |
May 18 2019, 10:50 AM
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#23
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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 |
Fixed!
I pulled the relay board and WD40'd the whole thing. I continuity tested between pin 14 and the 25 amp fuse, then to socket pins 30 on power and fuel pump relays. All well. I went to front and pulled two known good headlight realys and replaced both relays. Replaced battery in Meter for good measure. Powered everything up and went down to suspension console. Found 12V! Turned off ignition and went back to console, connected fuel pump wires and went back to ignition. Turned on and the fuel pump kicked on. Thinking water saturated board and with the WD 40 and cleaning it got sorted out. BTW Replacement board had no continuity between pin 14 and 25 amp fuse socket or power relay socket#30 and fuel pump relay socket #30. Now on to other productive stuff. Thanks again World. |
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