Hi all,
My Simjet 3000 start to behave strange, all of a suddent.
When running the engine 30% above idle it start to "pump".
It runs steadily for 2 sec, go down for about 1/10 of a sec and runs again 2 sec, down 1/10 of a sec and so on.
I appears all ower the range above 30% of idle. The aircraft is flyable with the problem, assume I lose about 5-10% of thrust.
But still, there is a problem.

The engine have performed excellent for about 15 hours of running. Before the problem occured, I discovered a fule leak, or say air in the fuel line. After fixing that problem the engine start to behave bad.

HELP, HELP, are heading for vacation and if things go good, visiting Holsterbro, Denmark.

Bengt T.

Hi Bengt

Where was the leak? Before or after the pump? Have you checked any filters you have ahead of the pump to see if they are clogged?

Ed

Hi Ed,

Thanks for the tyres you provied me a couple of months ago.

The leak was discovered in the fuel filter, the O-ring was broken. All were replaced by new parts and I couldn't see any air bubbles after that fix.

Can the problem be caused by the tempsensor?

Or can the FADEC re-programe it self due to the previous air bubbles in fuel line, to compensate?

If there is a leak after the pump, shouldn't it be just a problem with leaking fuel (fire hazard, smell in car etc.) and not causing any engine trouble?

Bengt

Hello Bengt:

What type of fuel pump do you have - Round Hausel or small brown colored Flight Works ? I just would like to know.

IF the fuel pump was run dry at any time during operation, it could have been damaged. It is possible that what is happening is that the pump is trying to get the engine up to speed but will not do so as it may be hanging up and then releases then hangs again. The fact that your problems all started with the discovery of the air leak in the fuel fileter which is located on the INLET to the pump may have had an impact on the pump.

Remove all fuel delivery lines to the engine and solenoids and blow out, including all fittings to insure that there is not dirt in any of them.

Disconnect the pump from the ECU and connect a 1.2 volt "D" cell flashlight battery across the pump and check to see if it has smooth, constent rpm operation. BE SURE to pump fuel thru the pump while performing this test.

Re-connect all tubing and restart the engine.

As for the thermocouple, they do not as a rule, pulse the engine as you have described. I belive that your issue is in the fuel delivery.

Thanks Kerry for you helping me.

I think I have found the cure!! When reading others conversations about engine trouble, I discovered an interesting thing, it said !QUOT! "move the throttle up and down slowly three times!! I did and the problem disappeared!! Something about ECU/FADEC computer self setting/adjustment.

Another problem have turned up during the past weeks flying. I got flame out when going from full thrust to idle rapidly. There is no bubbles or smoke, just flame out.
Can it be I'm flying an F15 Eagle (former D/F) with large intakes and by pass, creating a ram pressure. Can the flame be "blown" out of ram pressure?
I have cured the problem temporary by slowing down stick movement (computer radio) and always using at least 10-20 throttle setting as a minimum.