914 running rough ... Help, please.
in 912 / 914 Technical Questions
11 years ago
I have a strange situation, and I need advice.
Twenty flight hours ago, I was flying cross country at 9,500 ft.
The engine was running smooth at 4,800 rpm and 28 inches of MP (I was flying along with slower airplanes than my Pelican Sport 600).
I decided to climb to search for better winds, so I increased MP to 32 and rpm's to 5,200.
After a couple of minutes, the engine started to sputter, as if there was not enough fuel.
I immediately leveled the airplane, reduced MP and rpm's ... the problem semed to "disappear", not so my anxiety.
The closest runway was may departure point, so I made a 180 and started thinking ...
"What if the main fuel pump (which had been working already for 750+ hours) is already tired and not giving enough pressure?"
So, I increased power again and waited ... after some 10 seconds, the failure was there again, but this time instead of reducing power, I turned ON the auxiliary fuel pump.
That seemed to fix the problem.
I repeated the process two more times and the auxiliary pump always fixed the situation.
By then I was pretty sure that I had a tired main pump.
I arrived at home and a friend let me use one of is 914 fuel pumps (much newer than mine), so I replaced the main pump with my friends'.
I flew for more than 3 hours at 11,500 ft with only the main pump running and no problem!
So I went into Lockwood Aviation's webpage and asked for a new one.
Once installed I started flying again, apparently the problem was gone.
One thing I noted, the inner part of the muffler was completely black, and a lot of black powder was covering the inner walls.
Also, the spark plugs are VERY dark, all 8 of them.
That means very RICH mixture, right?
I wonder how comes if it was perfect for more than 100 hours, and then without even touching the carbs, the mixture becomes so rich?
Well, the thing is that the failure is not gone.
I replaceded all the hoses that go from air box to carbs and sensors ... nothing.
I cleaned carbs ... nothing.
Yesterday we measured the resistance values in the Throttle Valve Position Sensor attached to the 2/4 Carburetor.
It seems to be faulty, no reading at all between tip 5 and 7.
Could this sensor be a cause of all this mess?
Thanks for any help.
Twenty flight hours ago, I was flying cross country at 9,500 ft.
The engine was running smooth at 4,800 rpm and 28 inches of MP (I was flying along with slower airplanes than my Pelican Sport 600).
I decided to climb to search for better winds, so I increased MP to 32 and rpm's to 5,200.
After a couple of minutes, the engine started to sputter, as if there was not enough fuel.
I immediately leveled the airplane, reduced MP and rpm's ... the problem semed to "disappear", not so my anxiety.
The closest runway was may departure point, so I made a 180 and started thinking ...
"What if the main fuel pump (which had been working already for 750+ hours) is already tired and not giving enough pressure?"
So, I increased power again and waited ... after some 10 seconds, the failure was there again, but this time instead of reducing power, I turned ON the auxiliary fuel pump.
That seemed to fix the problem.
I repeated the process two more times and the auxiliary pump always fixed the situation.
By then I was pretty sure that I had a tired main pump.
I arrived at home and a friend let me use one of is 914 fuel pumps (much newer than mine), so I replaced the main pump with my friends'.
I flew for more than 3 hours at 11,500 ft with only the main pump running and no problem!
So I went into Lockwood Aviation's webpage and asked for a new one.
Once installed I started flying again, apparently the problem was gone.
One thing I noted, the inner part of the muffler was completely black, and a lot of black powder was covering the inner walls.
Also, the spark plugs are VERY dark, all 8 of them.
That means very RICH mixture, right?
I wonder how comes if it was perfect for more than 100 hours, and then without even touching the carbs, the mixture becomes so rich?
Well, the thing is that the failure is not gone.
I replaceded all the hoses that go from air box to carbs and sensors ... nothing.
I cleaned carbs ... nothing.
Yesterday we measured the resistance values in the Throttle Valve Position Sensor attached to the 2/4 Carburetor.
It seems to be faulty, no reading at all between tip 5 and 7.
Could this sensor be a cause of all this mess?
Thanks for any help.
