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New Electric Fuel pump failed after one month

swc65

Regular Contributor
Would like your feedback. I installed a Carter P4594 electric fuel pump, Low Pressure Oil Switch and a relay to run the pump about a month ago. Last week the pump failed. No warning signs, just quit. I applied 12 volts directly to the pump but it is dead. I don't know if it just failed or burned up. I confirmed the Low oil pressure switch is working and I confirmed the relay is closing. I put my Fluke meter in series with the fuel pump wiring and only measured 10.75 Volts. I know I should have 12 volts going to it from the relay I installed. I'll need to double check that measurement to insure I was properly connected. If I measure same voltage then not sure where I go from there. I spoke to Carter tech support and he confirmed that low voltage could cause a premature pump failure. Looking for any guidance in how to identify where the voltage drop may be coming from. I removed my battery and plan to have it checked. I confirmed that my alternator is supplying 14.03 volts with motor running and all accessories on with full load.

Not sure if the following would have had anything to do with it however, I had a slave relay for the start circuit which I cracked when terminating battery cable earlier in summer. I epoxied it, and it cranked the motor, I intended to replace but I forgot to replace it once the summer got started. The motor has been slow to crank when its hot, and I suspect that slave relay was the culprit. I have the control leg (Terminal 86) of the fuel relay connected to the ignition terminal of the Slave Relay because I could not think of any other ignition source to connect and didn't wan to run a separate wire all the way to the helm. My ket switch already has two ignition wires terminated on the "I" screw. I cant see how the slave relay may have affected the ignition terminal but perhaps it did. I've ordered a new fuel pump, slave relay and another fuel pump relay just in case.

I plan to double check the voltage of the fuel pump relay to confirm if its not getting sufficient voltage. If it is not getting at least 11.5 V then I need some guidance.

Relay wiring
86 - to Slave Relay "I" Terminal (16 AWG)
85 - To Battery Negative (16AWG)
87- To Fuel Pump Positive (12 AWG)
30 - Battery Positive - (12 AWG)
Fuel Pump Negative to Engine Block (ground)

What am I missing? Is is appropriate to terminate terminal 86 of the fuel relay to the "I" terminal of the slave relay?
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OK Update on this, I see I've got some views so I hope someone has some feedback. I had my battery tested and its bad at least per the Oriely's battery testing machine. I don't doubt it because it several years old. I can understand if the battery was weak and not providing enough voltage (or current) to the fuel pump. I'd like to take the time to install better battery cables and a battery switch while I'm at it. Ive done some research on components and think I know what I should do but would certainly take any advice based on experience.

My Calculations:

  • 1.7kW Starter = 141.67 Amps (@12V)
  • Bluesea Systems Circuit Wizard advises I need 4 AWG for my two 4 ft cables (positive plus ground) Good for 160 amps

Thinking of ordering custom made cables from BestBoatWire.com and buying a quality marine battery switch in hopes that I don't burn up the new fuel pump again. Also adding a filter before the pump in case there is any trash in tank.

I'll admit, electrical is not a strong suit so wondering why my pump would have failed on low voltage when my battery was receiving 14 v of charge by alternator while running. Fuel pump only runs while engine in running (and battery is receiving charge). I'm sure there is a simple explanation if anyone has one.
 
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