Rough Engine at High Altitude Airports

8 years 4 weeks ago #153 by Jen D
Replied by Jen D on topic Rough Engine at High Altitude Airports
Hi Dirk,

Here's what our tech expert Steve Ells has to say about it:
Dear Mr. Bondy;
I found a Lycoming Service Instruction (SE No. 1489C) that I think is applicable to your situation.This SI applies to TIO-540-AJ1A engines with part number 2576532-1 or 2576556-1 flow dividers installed. These part numbers are easy to see on the data plate of the flow divider.
This SI recommends that the 2 PSI spring in the fuel injection system flow divider (sometimes called the spider) be removed and a 4 PSI spring installed to IMPROVE IDLE CHARACTERISTICS. The part number for the 4 PSI spring is Precision 2577011; I found one on line for less than $4.
The purpose of the spring in the flow divider is to provide a clean idle cut off when the engine is shut down. Installing the 4 PSI spring results in a higher fuel pressure and more positive fuel delivery to the fuel injectors especially at low engine RPM and hot, high conditions.
If this SI is applicable to your T206, upgrade to the 4 PSI spring--installation shouldn't take more than one shop hour at most and then reset the idle speed and idle mixture settings on your T206 for operations at your normal home airport. The engine must be at operating temperature to set these values.
Due to seasonal changes in air temperature the idle mixture and idle speed settings should be checked and adjusted as necessary at least twice a year.
You as the pilot can perform a mixture check after every flight. This is done after the engine is at idle speed by slowly pulling the mixture control aft--the behavior of the engine will tell you if the idle mixture is just right, too lean or too rich.
Just right will reveal a slight RPM rise of 25 to 50 RPM; a too rich mixture will result in a RPM rise of more than 50 RPM, and a too lean idle mixture will cause the RPM to drop off without any RPM rise.
After the spring is replaced (if needed) and the idle mixture and speed are set you may still have to lean on the ground to get your engine to idle smoothly.
The confusion about the need to lean on the ground for smooth engine operation may result from the Pilot's Operating Handbook mandate that the fuel mixture always be full rich for a takeoff in your turbocharged airplane. This is the exact opposite of the need to manually lean for a mixture that results in best power at high altitude airports in non turbocharger equipped (normally aspirated) airplanes.
A turbocharged airplane such as yours is as affected by the need to lean during idle and low power operations as much as any normally aspirated airplane because the turbocharger is no longer boosting the manifold pressure as it is during high power engine operation. Hence the engine mixture is affected at high altitude airports such as Lake Tahoe and Big Bear. In short, lean as necessary for smooth engine operation.
Happy Flying,

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8 years 1 month ago #152 by K Dirk Bondy
Rough Engine at High Altitude Airports was created by K Dirk Bondy
I am the recent proud owner of a 2010 Turbo Stationair. I love it, but I've had a few issues at Lake Tahoe and at Big Bear (high altitude airports > 6000 msl). At both airports my engine has died on the ground with full mixture and idle power. I've gotten good at leaning properly and keeping in power on the taxiway, but I've been told the engine shouldn't have quit by a Cessna expert A/P. I've had the fuel lines checked, the air intake checked, and I even paid almost $3k for a new fuel servo. But it will still die at idle power at a high altitude airport. Has anyone else had a similar experience? Any advice?

Dirk Bondy

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