Hot Starting a Fuel Injected Lycoming Engine (IO-360)

The fuel injected IO-360 Lycoming engine in my Piper Arrow has always been difficult to start when it is hot but I finally found a technique that works quickly and reliably.

First, a bit of background on the issue. When an airplane has been flown and then parked for a few minutes, the engine, and everything in the engine compartment, is hot, all the more so with St. Louis summer temperatures in the 90s. Since avgas boils at about 135° F, vapor lock is all too common. When avgas in the fuel lines vaporizes in the fuel lines, bubbles form which block the flow of liquid fuel. Without a steady supply of avgas to the cylinders, the engine won’t start. Once vapor locked, the only real solution is to wait for the fuel lines to cool down sufficiently for the gaseous fuel to condense back into liquid.

New Simpler Technique

I learned an even easier technique in 2018. This works every time.

1. Master switch on.
2. Leave the mixture where it was when you shut down the engine, at idle cut-off. You can leave the electric fuel pump off, too; it doesn’t matter.
3. Open the throttle fully.
4. Engage the starter. The engine will start promptly.
5. Push the mixture full forward (full rich) and simultaneously pull the throttle back to idle.

Don’t be worried that the engine will over-rev or anything in the last step. You will have plenty of time to retard the throttle.

Old Technique

I wrote these instructions in 2011. This technique works, too, but is a couple more steps.

1. Master switch on.
2. Don’t touch the mixture. Leave it where it was when you shut down the engine, at idle cut-off. Also leave the electric fuel pump off throughout the starting procedure.
3. Open the throttle fully. Leave it open for a few seconds to clear the pressure in the fuel system. Close the throttle.
4. Open the throttle ¼” to ½”, to the point where you normally set it when cold starting the engine.
5. Engage the starter and the engine should start.
6. If the engine does not start promptly, open the throttle a little more and re-engage the starter. Repeat as necessary. Within a few tries, you will find a throttle setting which is right for combustion and the engine will start.
7. Immediately open the mixture fully.