Sudden Drop in Fuel Pressure and Power Loss on 912is

Well at least you know it is a fuel pressure problem. As Jeff said, replace the course filters and i would also replace the fine filter as this is the easiest to start. As Jeff said,you can pull the fuel line and see if there is fuel flow to the pumps with the CT gravity feed. If you test this before you replace the course filters, that will provide you more information.

It is unlikely that both fuel pumps would have the electric problem simultaneously, but who knows.

It first appears to be something of fuel supply since both fuel pumps are working and some single failure appears to be the cause.

In any case, I have had electric problems with the fuel pumps a couple of times. Once with the fuel pump switch going bad, once with the connection coming out of the fuse box pin corroding or loosing connection. However this is only for one fuel pump band you have two. so ?????

In any event, with all systems on, the fuel pumps and the engine not running, both fuel pumps should get 12 volts when you pull the leads off, and the ground wire is what the switch is connected to so that switch/circuit can be checked. 

Having a Rotax expert who understands the systems and can efficiently troubleshoot is your best bet.

That is what I know.....

Jeff Blakeslee wrote:

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.  

This is the most probable cause and best starting point. Simple to pull the fuel line going into fuel pumps and see that you get good gravity flow.

Has this problem occurred when the airplane is in different attitudes, like climb vs descent, turn vs straight?

The weird issue is he drops fuel pressure for just a moment then it comes right back to normal and running both pumps makes no difference.  If it was a filter it wouldn't just happen for a moment then return to normal. Plus he wouldn't be able to fly 8 - 10 times and then nothing happens. Because of the quick drop to 14 psi and then almost immediately comes back up to normal I'm thinking electrical connection

 It's like you wiggle a wire and the pressure drops then immediately comes back. The usually happens on decent. What changes,, air flow through the cowl and vibration through the plane even though you can't feel it.

I have another 912iS and the Lane light comes on when the throttle is pulled back and only in decent, but no issues with the engine. Cycle the key and it goes out.  Part of the issues are the Lanes recording / sensing routine. Lane A 100 times a second and Lane B 10 times per second. Any little electric connection wiggle and a Lane light comes on even though there really isn't an engine issue.  

This second plane is an electrical glitch, but I think Dan's is a true electrical momentary electrical cut out. All his other things have been checked like the gascolator and the filter. 

Any possibility of debris in the fuel line that is floating and periodically blocks flow? That's why I asked about attitude.