Fuel pump runs but no pressure

Main fuel pump (#1) runs but shows no pressure. Aux. (#2) runs and shows pressure just fine. Thought it was a bad pump so I sent the whole assembly to Lockwood and thought they would test both and confirm that main pump was bad but they just sent me a replacement assembly.

Put it back in and still have the same issue. Pump # 1 runs but never develops any pressure. Pump # 2 works just fine. Shows 43psi.

Used a volt meter to check the voltage on the power connections and both show 13.1 volts. This is when not connected to the pumps.

Swapped power leads and with the power lead for #2 connected to pump #1 it works just fine and shows pressure as it should. Pump # 2 now just runs and never builds any pressure.

What am I missing?

I’ve seen this happen with the pump installed backwards (or leads flipped). Any chance it’s running the wrong way?

Don't think so

Power leads are not reversed and the pumps are part of a dual pump assembly and they are oriented correctly based on the photos in the KAI. Plus, each one works fine when connected to the power lead for the # 2 pump.

Is it pumping fuel?

Voltage measurements are meaningless without a load connected.
An incandescent lamp make a good load.

Do you have a check valve in that none working pump that stuck or bypassing the fuel?

Solved!

Ok, so those of you that have worked on the fuel pumps in an RV-12is AFTER the tail section has been attached will understand what fun it is especially when you are 6'5". When I did my voltage checks I disconnected each pump's power lead , noted a red (positive) and a black (negative) and hooked up my meter accordingly. Didn't think to compare the plugs, duh.

So when all else fails talk to Bob Y and everything will become clear. Because he had seen one of the replies here he too thought the pump was running backwards which meant it had to be reversed polarity.

This morning I unplugged BOTH connections and compared them when they were oriented the same way. Sure enough, the wires on the plug for pump#1 were reversed. The wiring harness was built by Stein Air so I guess it slipped through their QA process.

Didn't have the tools to pull the pins and switch them so I just cut the wires flipped them and put them back together with an in-line splice.

Now both pumps show 44psi. Yea!

Thanks to all that replied.