Odd fuel pump behavior

[redlanternzebra]

Hello forum, hoping for your help with a problem I don't understand; here are the details: 1985 k100 with aftermarket ECU and standalone fuel pump relay. Relay is engaged when ignition is set to "on" in order to prime the fuel system. I measure ~12.4 V at the fuel pump leads. When the pump is connected and powered by the relay, it just "clicks" but does not spin or pump whatsoever, as far as I can tell. This same behavior is exhibited when the pump is connected directly to the battery. I think the battery is good because it drives the starter just fine. If I connect the pump to a DC supply reading ~13.6 V, it DOES spin as one would expect, pulling about 9 amps. This pump was new two years ago and unfortunately sat in gas for two years, it's possible this is having an effect. I thank you in advance for any advice you might share, and I hope to share some progress from this project soon.

[frankenduck]

I have no idea what your ECU does or how you have things wired but the factory fuel pump only operates when the engine is turning - when starting or running. It does not prime the fuel system.

[redlanternzebra]

The ECU has a programmable fuel pump run time at power on. I believe all this is working correctly, as I register a "click" from the relay and measure voltage at the fuel pump leads which cuts off at the end of the priming duration. The same behavior happens when the starter is engaged for what it's worth. How can I explain the lack of normal function at the pump when it is receiving 12.4 V, while it does function correctly at 13.6 V?

[Tnbill]

Have not tested one but 9 amps sounds high judging from the stock fuse and wire size. Also the voltage increase you stated is almost 10 percent.

[redlanternzebra]

Success! Tnbill, you were on the money. Pump was seized. What I perceived to be correct functioning with the higher voltage was in fact a frozen motor. I reversed the polarity on the pump and showed it a little carb cleaner to restore the function. after clearing the gunk, current draw when free spinning is ~1.7 amps at 13 volts. Reinstalled the pump and started the machine. Thank you for your help!