Poor Starting 912iS

Bill Hertzel wrote:

Reviewing the magic equation again. Fuel + Air + Squeeze + Spark = Bang.

The Air is mechanically controlled by the Throttle.
The squeeze is fixed by the design.
The spark is controlled by the ECU.
The Fuel supply appears to be good but the injection is controlled by the ECU.
It would appear that the ECU is NOT detecting some event that it expects to see and shuts down the fuel and spark.
On the second start, the missing event occurs and all continue normally.
That missing event should be in the ECU Log file.
- - -
While we are waiting for the ECU swap ( I do not have a warm feeling this is going to be helpful, but I have been wrong a lot lately)
Let's try this...
Turn on the fuel pumps, Start Power, and both Lane Power switches.
Then wait an actual full minute before cranking.
If it a sensor that is slow in initializing, this start would be occurring at about the same time as a normal second start.

We might also try starting with only a singe Lane A or B powered up instead of both and see if it makes a difference.
The engine normally starts on B so Try A ON, B OFF First.
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Also if the ECU Swap solves the problem, do not call it solved until you reinstall the "BAD" ECU and confirm the problem returns.
The problem may just have been a marginal connection that was resolved during the swap.

I took your advice and waited a full minute with the pumps on prior to start.  The engine started and ran fine on the first attempt.  

 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.

Pumps and lanes were energized.  I'll try pumps only and lanes only next time I'm at the airport.  Thanks for your help!

I should have an ECU to try this weekend, its in the Post......

I kind of agree with Bill that it isn't an ECU but it is an easy thing to try.

The UK Rotax Agent thinks it could be the Sprag Clutch on the Starter not spinning the engine fast enough,

the jury is out on this one. Changing a sprag clutch is an engine out and a couple of days work, I will try the

easy things first.

I have been following this interesting thread closely as the issue is a learning experience for me. I have one question: the operators manual (page 3-7) states that only one fuel pump is to be turned on for start as both on "can lead to bad starting behavior" . In the last posts your check list is calling for both pumps to be on. Is it possible that both on is contributing to the problem? Richard