Fuel pump pressure drop

Actually sounds like you're on the right path. Could be the one pump. Nothing mechanical is always 100% bullet proof.

Robert:

Is the sound of your main pump just a slightly different pitch, or does it sound labored and inconsistent? They naturally have a little different sound because of the fuel routing through the check valves. 

With about 200 hours on my 912iS aircraft (a few years ago) my main fuel pump was running a bit slower and less confident sounding than the aux pump. I traced the problem back to a high resistance connection on Socket 11 of the X-1 (Lane A) connector on the bottom of the fuse box assembly.  The socket in the #11 position feeds the main pump and it was discolored and oxidized like it had been hot.  I believe the heat broke down the spring tension in the female socket causing a poor connection. I replaced both the pin and socket in that connector and the problem was resolved.

Also, during the maintenance you describe if you removed and then reconnect the electrical connector at that pump you may have improved the connection temporarily.  You could try swapping the connectors at the pump so that the pump 1 switch operates pump 2 and vise-versa. If the problem stays with the SAME SWITCH, then it's an electrical problem. If the problem moves to the aux pup switch (now running the main pump), then it's a pump problem. 

When you are troubleshooting keep in mind that the switches are on the negative leads to the pumps.  The positive leads are hot to the pumps any time the engine is running or start power is applied. 

When a 912is pump stops so does the 912is! Personally I start on one then leave the other on until landing for my confidence level. Was wondering, for such a critical part, is there a MTBF based replacement requirement? If not why not? Have there been any recorded accidents attributed to fuel pump failure?

lastly what is the price for one? 

Thank You!

Thanks for the replies. The price was six something with a several month lead time having none in stock in the US. 

I always use both over critical terrain water and low level flight. If I had an engine failure I would automatically assume the pump died and turn the other one on and try a start.

Bob

Doug,

The rubber connector tubing between the pumps must be replaced every 5 years with the rest of the rubber change.  Every 1000 hours the main pump is to be replaced and the aux pump is to be inspected.  Based on that maintenance schedule, it appears Rotax intends, or at least expects, that that the aux pump will be generally held in reserve rather than run full time.  If the owner chooses to run both pumps full time, then it would seem prudent to replace both pumps every 1000 hours.