On 13-Dec-2004, zatatime wrote:

I think this is the correct "guess." Induction icing can occur in the
60 degree range without a problem if you have the right conditions
(i.e. moisture, which you had alot of). In your original post you
stated you put on an alternate air source of some sort to bypass the
air filter. Check with your mechanic if this gives heated air to the
mixture. If so this is the equivalent of carb heat, and could be how
the problem resolved itself. If not, check to see how to provide warm
air to the induction system. Even if you've got to make a
modification (install something), it'll be worth it.


Induction air heating is not required for injected engines because intake
air is not cooled like it is in a carburetor. Induction icing in an
injected engine means that frozen (i.e. snow) or super-cooled water in the
atmosphere freezes in the induction system (usually in the air filter) and
restricts airflow. The alternate air system bypasses the air filter to
solve the problem. Source of alternate air in most injected airplanes is
from within the cowling, so there is some warming effect. The Mooneys of a
certain vintage used their "Power Boost" system to double as the alternate
air, so their alternate air source is ram induction.

In this case induction icing as the problem is extremely unlikely for two
reasons. First, it is not likely to occur with an OAT in the 60 degree
range. Second, induction icing, or any other problem that restricts intake
air, would result in an excessively RICH mixture, and engine roughness would
then be reduced by LEANING the mixture. In this case engine roughness was
reduced by ENRICHING the mixture, which indicates that the problem lay not
in the intake air but in the fuel system. Water in the fuel is certainly a
possibility, but since the problem did not resolve by switching tanks
(assuming the pilot gave it a few moments for this to work before switching
back) I think a more likely culprit would be one or more partially clogged
injectors. I would have a mechanic inspect the fuel system from the
gascolator through the injectors to make sure that no contaminants remained.

--
-Elliott Drucker