… when I am rewiring the fuel pump, do I need both the high and the low speeds?  My dumb question of the day is, when is the fuel pump supposed to be used on the TSIO550 in the Lancair IVP?

 

Dan,

I was advised by several owner/fliers to run the boost pump in “low” speed above 10,000’--only. A good friend with lots of experience in Lancair IV-P’s runs his fuel pump on low at all times. I have chosen the former route, and have an altitude/pressure switch hooked to a light that reminds me to switch to low boost when passing 10,000’ climbing, and to turn it off when descending.

 

I have set up the engine to flow 43 GPH at 2700 RPM and 38.5” MP on takeoff with the boost pump off. Turning on the low boost raises the fuel flow about 2 GPH at max power, but high boost increases it so much that the engine floods/quits—48 GPH or so.

 

I intentionally left the low boost off after heat soaking at an airshow during climb out two weeks ago. The engine rolled back at about 14,000’ and the fuel flow was erratic (I did not look at the pressure, but will do so if it happens again…) I turned the boost pump to low and the engine recovered almost immediately…

 

So for my money; boost pump off for all operations below 10,000’, and on above. Keep high boost for purging/starting, and any time you have fuel starvation, such as vaporization or loss of the engine pump. Expect to have to modulate the fuel flow manually with the mixture control any time you’re running high boost…

 

Views of others?

 

Bob