I have an intermittent fault in the CB/switch used to turn this on.
If the answer is NO then this seems to be a potential way of getting stuck somewhere.
I think the engine-driven pump will eventually draw in fuel but it could take a long time… Has anyone tried this?
Obviously the CB will be changed before the next flight.
Not tried, but a colleague with an IO-540 had a broken aux fuel pump and said: no way will it start, he tried 🤪
I only “prime” with the aux pump as per the manual, until there’s a fuel flow indication in the gauge. But I start my engine without aux pump. No difference!
So in my opinion it could start without.
I think it’s a good point that one could try out at home, without too much stress on the starter of course.
It will most probably be different when you try to start. The next day should work best. Not too long but not hot anymore.
My shop has experience with an IO540 in a TB20 stranded without a broken fuel pump.
It wouldn’t start, even with repeated, timed starting efforts (to not wrar the starter).
Apparently, the battery is dead from turning 6 cylinders and a prop before the engine driven pump pulled enough fuel to start the engine.
I actually never understood the starting procedure of the io-540. You prime the engine with mixture forward, then cut it off, start the engine with mixture cut off (mine starts very good right away) and then pull it back forward again. Why is that so?
Because withaut aux pump you can only try with mixture full forward. Without being able to adjust a good mixture.
The cold start fills the fuel lines all the way to the point where the fuel distributor (the round thing on top of the engine) is filled (the fuel pressure gauge is fed from that) so the engine needs only to fill the (internally very thin) steel fuel lines afterwards.
Hot start – I am not sure. It basically floods a part of the fuel system.
My shop has experience with an IO540 in a TB20 stranded without a broken fuel pump.
It wouldn’t start, even with repeated, timed starting efforts (to not wrar the starter).
That’s a priceless reply – thank you 
Don’t understand it either and when only saw this strange procedure after several months flying ;-) did get a different (wrong?) Introduction by the insurance-demanded instructor and stuck to it.
Have started my IO540 for >700hrs w/o mix cut/off. No issues either.
May be to reduce the fire risk in case of a misfire at startup ?
Maybe a daft idea, but I wonder if in extremis, say stuck at some small airfield with no mx, you could pull the engine through manually until the fuel lines are filled. You’d probably have some sore muscles, but could that work?
UdoR wrote:
I actually never understood the starting procedure of the io-540.
IME that how all (Lycoming) fuel injected engines are started.
Certain the io360 that was in the arrow 2 that I used to fly was also stated that was (mixture cut off).
I once was able to start an IO360 without the electrical fuel pump. It took at least six starter runs and some fiddling with throttle and mixture. I was extremely stressed because once I got it going it was single digit minutes before closing time of the departure airfield and another night in the hotel. 60 minutes later I landed 2 minutes before closing time at my destination. Due to the stress I wasted (mixture closed as per the manual) the first two or three tries without realizing what’s wrong. I believe with knowing of the issue beforehand and with the correct procedure it should work much better and with less stress on the starter motor and the battery. Now, an IO540 has 50% more cylinders than an IO360 but then the battery also has 50% more capacity so in the end it shouldn’t make too much of a difference.
