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Poor Starting from cold - Starts, Runs for 1 - 2 secs then Stops - takes 4-5 goes before it runs OK

Notices Gurgling Noise in Fuel System, near Fuel Pressure Regulator.

 

We have been running a 912iS Engine for 4 years, this is our 2nd Engine the first one did 1240 hrs before we changed it due to high maintenance and the 2nd Engine has done 500 hrs. Apart from all the other problems they have all started well, first press of the button. However, within the past few weeks the engine fires up but stops after 1-2secs, it then takes approx. 4-5 goes before it starts, once started it is Ok for the rest of the day.

Things we have done.

1. Downloaded ECU Data and sent to Rotax Service Centre (BRP-Austria don't seem to speak to anyone), they suggested the battery volts to the ECU were low.

2. Replaced Battery - higher capacity one - No difference still poor initial cold start

3. Removed and Cleaned all Connectors, Plugs, Fuses etc (Rotax still won't supply a Circuit Schematic for the Fuse Box or a Wiring Diagram)

4. Changed Fuel (Coarse & Fine) Filters

5. Noticed a gurgling noise in the fuel system with Pump(s) on - no engine running. This was coming from the Fuel Pressure Regulator.

6. Removed Fuel Pressure Regulator - inspected internal screen - all clear - re-fitted - still gurgling noise with Pumps on

7. Checked Pressure 3 Bar (43.5 psi) all OK

8. No fuel leaks

9. Spotted an Old Post with someone who got Air in the System and had similar starting problems

Has anyone else seen this ?

Regards, Malc

  • Re: Poor Starting 912iS

    by » 3 months ago


    I have this exact same issue.  Search for my post titled "Start then Stop"  There's 4 pages of speculation.  My engine started and ran fine for the first 3 years of ownership, then all of the sudden this starts.  I have 700 hours on my engine. 

    Do your lane lights come on during any of the start attempts?


  • Re: Poor Starting 912iS

    by » 3 months ago


    Sometimes the Lane Lights come on, but once the engine is running they can be cleared by cycling the Lane Switches.

    I am going to substitute a new ECU at the weekend just to eliminate that component. I still think it's something to do with air getting into the system, hence the gurgling / cavitation near the Fuel Pressure Regulator.


  • Re: Poor Starting 912iS

    by » 3 months ago


    Malcolm Huddart wrote:

    Sometimes the Lane Lights come on, but once the engine is running they can be cleared by cycling the Lane Switches.

    I am going to substitute a new ECU at the weekend just to eliminate that component. I still think it's something to do with air getting into the system, hence the gurgling / cavitation near the Fuel Pressure Regulator.

    Same here in regards to the lane lights.  Let me know how the ECU test goes.  

    PS - I sent my BUDS download to Lockwood today.  I'll let you know what they say.


  • Re: Poor Starting 912iS

    by » 3 months ago


    By the way, we are not the only ones with this issue.  I've spoken to 2 other iS owners with the same issue.


    Thank you said by: Malcolm Huddart

  • Re: Poor Starting 912iS

    by » 3 months ago


    This is just throwing an idea at the wall and seeing if it sticks...wink

    Let's assume you are getting Air in the Engine Fuel Rail.

    Let's also assume this is a problem with aircraft with low wing tanks.

    "The question is, "Why, what changed?

    The fuel pressure regulator is designed to restrict fuel flow to maintain pressure.

    It is essentially a restricted one-way valve.

    It is not necessarily designed to prevent a reverse flow.

    When the fuel pumps are shut OFF and the pressure head in the fuel line tries to backflow, the fuel pumps provide a reasonable but not an absolute restriction.

    Under normal circumstances, the fuel will drain slightly and pull a small amount of air through the Fuel bypass orifice into the fuel line before the engine up to the point that the fuel is level with the fuel in the tanks, and the pumps lose their prime.

    When first starting the fuel pumps, the air is purged out the bypass orifice, the pumps regain their prime, the fuel pressure comes up to nominal and any remaining air is quickly pumped out past the pressure regulator.

    Now let's assume the bypass orifice has become blocked.

    After shutdown, the fuel lines backflow and drain through the pressure regulator, draining the full fuel rail in the process except for a small amount of fuel in the fuel injector side tubes.

    Now, when we attempt a start, the fuel pumps can not regain their prime until the air is cleared from the fuel rail.

    The pressure regulator is not going to open until it sees 40+ psi and the fuel pumps can only pump air at ~3psi

    Once you start cranking the fuel injectors initially use up their small amount of fuel after a few seconds and then the engine dies.

    Subsequent restart attempts allow the air to exit out the injectors to the point the fuel pumps regain their prime and are able to blow the remaining air out the pressure regulator.

    All is once again right with the world.

     

    If the culprit is the Fuel bypass orifice,  look for these symptoms...

    Does the fuel pressure fall to ZERO within 5 seconds after removing power from the fuel pumps?

    Does the fuel pressure reach 40+ psi within a few seconds after first powering the fuel pump after an extended shutdown?

    Can you hear the fuel pumps pumping air before regaining their prime?  

    This will sound like a high-speed whine followed by the pumps slowing down as the pressure comes up.  

    This will take less than a second if they are already primed.  

    The difference between "Meowwwwwww" and "Meeeeeeeeeeeow".

     

    Do you perform the fuel pump check before the engine start?

    Is your fuel pressure in the green and stable before the first start of the day?


    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    whertzel1@yahoo.com
    Clicking the "Thank You" is appreciated by all.

    Thank you said by: Malcolm Huddart

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