fuel leaking from FI airbox
 

Trying to figure out why fuel was leaking from the airbox on a FI engine...

Here's the story. The battery was dead last night and so we hand proped the IO-320-E2D. We tried mixture rich settings/throttle 1/8 open & mixture cut-off/throttle full settings. For each we built pretty good fuel pressure just hand propping it and both times fuel began leaking from the airbox. Left a good 1 ft diameter spot on the concrete...so that's quite a bit of fuel (fire extinguisher close by).

I'm guessing since it's FI'd that the fuel was sprayed into the cylinders, then leaked out of the intake valves down to the airbox, then along the lower cowling to the ground? Not sure why any fuel would be delived with the mixture in cut-off though.

I just don't understand exactly what's going on here and why hand propping it would make a difference than using the starter.

If anyone has some experience on this, I'm very interested. Maybe there's a rule out there I don't know about that one shouldn't ever try to hand-prop a FI engine...haven't heard that, but who knows...

Thanks!

-Jim

P.S. Ended up jumping it with another battery and it started right up.

Fuel is not sprayed into the cylinders, it is sprayed behind the intake valves. Normally, when the valve opens the fuel is sucked into the engine. If too much fuel accumulates it runs back down the intake runner and drains out the sniffle valve or collects in the airbox in your case. Aircraft fuel injection is not like care fuel injection when the injector is right inside the combustion chamber.

If you think about it, aircraft fuel injection should be called "fuel flow" not fuel injection. When the engine is running it is a contestant flow based on throttle setting. It never stops.

Thanks guys--starting to make more sense. So what is the constant flow intake body injector doing to the fuel/air mixture while the intake valve is closed? I guess making the air more and more rich until the fuel rich air is sucked in to the cylinder. Just curious. -Jim

Actually most car gas injection injectors dump the gas on the intake manifold side of the intake valve also. Only a few newer (direct injection) engines inject straight into the cylinder.