Fuel pump use on io engines with precision silverhawk injection

[ssturges]

Just finishing up my 9A(IO320-D1A Silverhawk) and done some initial ground runs. I have seen this referenced before that you only use the fuel pump for about 2 seconds to prime on start. Any more and you put fuel into the FAB and it leaks out through the hole in the FAB there for that purpose. I also confirmed this by leaving it on a sec or so longer than that, kind of shocking how much fuel comes out.

My question is what happens in ground running or in flight when your run the boost pump? The thought of flooding fuel/vapor into the fwf with a hot exhaust manifold near by scares me. Does this not happen when the engine is running and you use the boost pump? Or is this only an engine off thing? It seems like the boost pump is going to provide way more than needed while the engine is running and this would happen while then engine is running?

Some of the hot start procedures also seem like the would create this kind of fuel leak into the FWF.

I googled quite a bit for this but could not find any guide to this. Clearly people are using boost in different phases of flight, what don't I know here?

[DanH]

Steve,

My question is what happens in ground running or in flight when your run the boost pump?

Nothing, other than raising line pressure between the electric pump and the engine-driven pump.

Here, read this...basic operating principles of a Bendix-type fuel control:

https://www.danhorton.net/Articles/B...yond%20(1).pdf

The old Bendix RSA manual is also useful. Your Silverhawk is fundamentally a billet body RSA-5.

https://precisionairmotive.com/wp-co...6/15-812_b.pdf

[Ralph Inkster]

I also was taught to hold the boost for "2 seconds", I learned to use very little boost & vary it only as required for colder temps.

[ssturges]

Thanks Dan, that is a great write up. Everyone with fuel injection should read. In all my reading on here I was surprised I had not seen if referenced.

I am going to avoid any hot start technique that suggests you use the boost pump to clear the vapor. I have seen that posted a few times.

Steve

[RV7A Flyer]

I've had good luck with a) following the Lycoming manual for starting, and b) watching for about 2.5-3.5 GPH on the flowmeter (which coincidentally is about 3s or so, just as the manual says) when priming, for cold starting. For hot starts, no prime is necessary, just advance mixture as the engine starts to catch. Almost never have a problem with hot starts (once in a great while it may take twice to get it to start up, but it's rare).