Voltage drop

Well look. It does not seem to me you are actually checking anything. When checking voltage drop in a system you must check each possible point along the way and measure every single terminal, switch, and connection.

You can do this two ways......clip your meter to battery ground and measure each voltage, and note them, and compare them...........

Or clip your meter to battery PLUS and the drop along the way will be shown immediately

Follow this example path in your head. Let's say we have power to the pump from the starter relay, through a breaker, through a crash switch, and to a relay, and that the relay is activated by the key "ign" circuit. We can ignore the IGN circuit and troubleshoot just the power circuit

So we have starter relay...........breaker..........crash switch..........relay.............to the pump..........to ground

So get a long piece of wire, long enough to reach from the battery to every place your meter needs to access. hook solidly to a battery PLUS point, and best if you fuse that with a low value fuse. Hook "safely" to your meter, and activate the pump

Measure at the pump side of the breaker. Should be zero or nearly so. Measure both terminals of the crash switch. Should be zero on the breaker side and near zero, maybe 1/10 of one volt (.1) on the pump side.

Now check both relay terminals, the contacts. if you had .1 on the relay side of the crash switch, it should be .1 at the relay, and maybe .1--.15--.2 on the pump contact. Now go to the pump. The pump terminal might be say, .2-.3, because by now the wire length (to the pump) is adding up. NOW STAB the meter onto the pump itself or the pump ground wire. It should read "same as battery." Exactly.

Or, move your extension wire from battery PLUS to battery GROUND, and stab meter into the pump ground/ pump body. Should be ZERO. if something is dirty, there, the pump might not be grounding

Next, would be current. you will never know if the pump is drawing too much current, if you don't check two things..........the pump specs for maximum current, and then measure it. If the pump is drawing much more than spec, then obviously something dragging in pump

Also how about pump plumbing and filters? If the return is plugged, or a filter plugged, the pump might be drawing over current.

How about pump pressure? Does it develop rated pressure?

And last you might need to uninstall the pump and test it for the same conditions above, to control it's operating conditions.

Now I might be full of crap. It might be a bad pump. If you like throwing money at it , go ahead. How much is those pumps worth? One of my EFI pumps is over 200 bucks