Sudden Drop in Fuel Pressure and Power Loss on 912is

Daniel,

First, I would stop flying the aircraft until this is worked out.  If you have already switched to 100 LL vapor lock is unlikely to be the problem. 

Check the coarse fuel filter that is in front of the pumps.  This should have been done at the annual but you never know. A clogged filter here would starve the pumps and affect pressure with one or both pumps running.  With a newer airplane there could be construction debris that made its way from the tank to the filter.   And then disconnect the fuel line to the input of the fuel pump and verify good fuel flow to the pumps.

As you say, it could be an electrical issue, but the main pump and aux pump are wired independently. Because this problem has happened with both the aux and main pumps running that makes an electrical problem unlikely.  The ground wires from each pump originate at the regulator A ground plate, then run through the switches and out to the pumps. You could check the wire connections at the regulator A ground plate, it’s possible both pump ground wires are on one stud that has come loose, but that’s unlikely. The 12V+ wires for each pump are also independent and originate at the Rotax fuse box. Each pump has its own fuse.  

You can tell a lot about the pump operation by listening to them.  If you have a battery charger with a 10 amp output, connect it and do an extended run of each pump without the engine runnng. You can watch the fuel pressure but also pay attention to the sound.  The sound should be steady and consistent in pitch. If the pump slows or is starved for fuel you will hear it.  

Jeff: thanks for your very helpful reply.  My mechanical skills and knowledge of aircraft systems is pretty limited and I don't have many tools down in Sedona (I mostly live in Idaho), but I'll try to run some of the checks you suggest and I'll see if I can get some help from one of the local, experienced pilots.  I assume you don't live near Sedona as I'm more than willing to pay for an expert to come and help me out!

I think Roger Lee lives in Tucson, maybe he will reply to your other post. 

I've spoken to Roger Lee a couple times and he was very helpful, but unfortunately he doesn't offer mobile services.  

Maybe you could ask the mechanic who did your annual if he cleaned the coarse filter in front of the fuel pumps. Depending on the aircraft, this may be an inline filter or a gascolator.  If he did it should be in your logbook(s).  Most 912iS aircraft call for this to be cleaned in the first 25 and 50 hours and then at each annual.  The thinking is that any manufacturing debris in the tanks will wash out into the filter in the first 100 hours.