Poor Starting 912iS

Bill Hertzel wrote:

Malcolm,

It is highly unlikely to be a Sprague clutch problem.

If you keep reporting that it doesn't start on the first attempt.  This might be confusing for your dealer.

It DOES START in the First Attempt.  What it doesn't do is keep running.

And because it DOES Start, it is turning fast enough, so it is NOT a Clutch problem; And 1 second later it is turning fast enough for the generator to bring the battery voltage above 14v, so it is also not a voltage problem.

The ECU is not detecting any faults because any Air in the hoses and/or the Fuel pressure are not visible to the ECU.

It still feels like a fuel problem.

Try my modified checklist from a few posts back. it worked for Jim.

Ii would look at getting a bypass orifice installed.

The modified start procedure that Bill recommended has worked for me during the last 6 starts.  It's worth trying it out...

I haven't had much time to do any investigations recently. It still struggles to start but once it is going it will start and stop for the rest of the day without any problems (we did 20 starts with it last Saturday). I tend to agree with Bill that it is a fuel problem - I have thought that since day one, but I had to eliminate all the other stuff first. I am not convinced it is a sprag clutch problem neither.

The UK Rotax agent is going to lend us a Pressure Sensor that is covered in SI-PAC-020, which is used in conjunction with an oscilloscope so we can monitor real-time fuel pressure - this is the next step I will keep you informed of the outcome.

The modified start procedure seems to work most of the time; however, I did have a start then stop the other day.  

I tried Bill's start procedure without any luck. We will get to the bottom of it eventually but having looked after

the aircraft for 4 years, every fault like this just takes time.

I replaced the Fuel Pumps at the weekend - still no better at starting - just another component eliminated.

I also discovered that the Electrical Fuel Pressure Sensor that feeds the Stock EMU isn't reading anything

sensible, whether it is a failed sensor or the EMU loading the sensor I don't know, it reads a constant 0.75v.

I was hoping to hook an oscilloscope up to it to monitor the pressure at start-up etc.

I did put an analogue pressure gauge in the fuel line to the injectors and with the pumps on it read 3-Bar, and

there was no gurgling noise from the Pressure Regulator. With the Heath Robinson set-up I couldn't really start

the engine (hence why I was hoping the Electrical Pressure sensor would work).

Slowly chipping away at it....