Bad Fuel Pump

So I got an early Christmas gift a few days ago when I was out at the hangar again. The task was to determine a bit further if the fuel pump had an issue or not. I had made some flared tube stubs that would allow me to hook up tubes to the pump while it was in the fuselage and pump some gas in a closed circle - just to see how the pump rate was.
Before I attached these stubs, I decided to remove the inlet fitting after fishing in there with a tiny hook and finding some small pieces of unidentifiable debris.

What I found was traces of rust on the inside of the fitting. I grabbed my inspection camera and got a photo of the inlet side of the pump.

The shots taken from the screen of the camera are a bit blurry but I think you can still see the problem clearly enough,

Where did the rust come from? Well, I thought of the best way a while back to pressure test the fuel system before putting gas in it. Back then I decided to use distilled water which I tried to vacate after the test using pressurized air. Obviously this was not enough to get it out or maybe it just wasn't a good idea to put it in there to begin with. Either way, the pump had to come out.

Before doing that (which I deemed a multiple days job) I wanted to see if the pump really was the problem for limiting the flow in the fuel system and so I hooked up the tube stubs (after tightening the fitting again) and attached some PVC hoses to pump gas around in a jerry can.
Well, the result was inconclusive. The pump does slightly restrict the flow when blowing into it from the intake side but not enough to cause such a restricted flow as I had seen when doing the last-gallon test. When pumping real gas, it did do a pretty decent job in my eyes. It showed much more flow than I had seen during the last-gallon test. But then, I had also messed with the system since then quite significantly, so maybe the problem had disappeared or at least was mitigated at this point? I also do not remember seeing any problems during the First Flight and I did pretty much the same long and steep climb out at WOT as I did on the second flight when I saw the flow/pressure problem.
While the pump definitely has to be replaced because of the obvious rust problem, it is not yet clear to me that the pump was the only cause for the problem I had seen. There still could be something wrong with the tank as well.
For now I had to take the fuel pump out though and that was something I had not looked forward to at all. Before ripping everything apart I wanted to give it a serious try to remove it without further unscrewing of bulkheads and seat pans and such.

I drilled out the 4 rivets on the belly to get the shelf loose to which the pump is screwed on to. This was necessary as the pushrods prevent a direct access to the AN4 bolts that hold the pump to shelf and I did not have any tools to work around the rods. With shelf loose I could move sideways just enough to get a socket to them to remove them. With the pump disconnected from any mechanical restraints, it was fairly easy to detach the electrical connection as well. The pushrods were detached at their aft connection point to the torque tubes so I was able to spread them easily and with the pump being moved aft I was able to get it out by turbing it 90 degress while pulling it up and away from the tunnel. The distance from the flange on the bottom to the intake and outlet fittings is just enough to clear the pushrods with a 90 degree turn and then it was free.

One additional problem I have seen once the shelf had come out is that I had primed the flange area between the shelf bottom where it touches the belly skin. The flange has to make electrical contact for the ground of the pump though and at this point it could only do that through the 4 rivets that were holding it to the skin. I do not think that was a very good connection and it might have limited the current for the pump as well. I removed the primer with MEK and will not reprime it but maybe put some conductive grease on it when putting it back in.

The new pump is at home in the shop and will be readied with fittings and electrical connector to be a drop-in replacement for the rusty one.

The fact that the pump came out so "easily" will make the further work so much nicer and was a great Christmas gift! Now I can put the replacement pump in and test it much quicker than I had anticipated. I might still have an additional flow problem but at least I did not have to remove the seat pan, bulkhead and the flaperon servo just to get the pump out.

Merry Christmas!