Poor Starting 912iS

I'm not following the logic here.

IF

10v on start is a problem,

AND

The battery is replaced,

AND

the voltage still drops to 10v,

THEN

The new battery did not rule anything out. 10v would still be a problem. 

Recently there has been an ASB-912i-011 published on the Fuel Pump Assy. Our Engine wasn't in the S/N affected but

it never said what the fault was - doesn't anyone know ?  and could this affect other S/N causing our starting problems,

just a long shot.

That thought crossed my mind as well.  The ASB states: "Possible effects might be rough engine running, unusual engine operating behavior and possible power reduction or engine stoppage."

The fuel pumps have only one purpose; Move fuel under pressure.

Rough engine running and/or stoppage will be the effect of insufficient Fuel Pressure.

If you have good pressure your pumps are doing their job.

- - -

10 volts while cranking is normal.

If the engine starts for even 1/10th of a second, the voltage was sufficient.

The "B" generator is connected to the ECU BUS before and during Starting.

Notice that the Battery voltage immediately jumps above 13 volts once the starter is released.

This is due to the "B" generator voltage back-feeding through the START POWER Connector. (X3-2)

A few seconds later the "A" generator takes over powering the ECU and the Start Power is disconnected by the Relays withing the Fuse Box. 

At this same time, the "B" generator is transferred to the MAIN POWER Connector (X3-3) and the battery continues to be recharged and the airframe power bus is energized.

- - -

If the engine starts and runs for a few seconds before shutting down, it is Not a voltage or Fuel pressure problem.

A possible solution from another similar thread on this forum indicates that powering up the fuel pumps and the lanes for 30-60 seconds before attempting a start results in a good start.  The reason is still undetermined.

Bill Hertzel wrote:

 Now we are getting somewhere!!! 

Your reply is somewhat vague.

Was that with the pumps AND the LANES energized? Or, Just the PUMPS?

If it was with both, try it with PUMPS Only and LANES Only.

Once you find the culprit, Try it with a 30-second delay. 

I am going to guess it is a fuel issue and it just takes longer to clear than we expect.

The solution may just be as simple as moving the Pumps ON step farther up the checklist and performing the fuel pressure check BEFORE engine start.

- - -

Start Power ON. 

Pumps ON Both.  Pressure OK.

Main Pump Only.  Pressure OK.

AUX Pump Only.  Pressure OK.

Pumps ON Both.

Lane A Power ON.  Lamp Clears.

Lane B Power ON.  Lamp Clears.

Throttle Open 50%.

Propeller "CLEAR!"

START!

Etc...

- - -

By the time you get up to the START Line item, you should be good to go.

 

I tried your recommendation today and it started up on the first try and didn’t stop.