IO-470-N Engine Stalling

An item to look at is the sniffle valve which is located just behind the fuel control on bottom of engine. There is a small tube attached to the valve and goes overboard on right side below cheek panels.
You can blow into the tube very softly and you should feel is seal off. If it does not seal off, remove the valve and clean it carefully. When stuck open it allows additional air into the intake manifold causing engine to run lean.

You may be running lean at idle. Run the engine up until the oil temp is in the green.
After temp is up, run up to 1500 RPM for 4-5 seconds and then pull throttle to idle at 600 RPM. Immediately start pulling mixture back slowly while watching RPM. You should get a rise in RPM 30-50 before engine shuts down.
If no rise, engine is to lean and needs adjustment.

I would also suggest completing a fuel system setup (97-3E) if not done in last couple of years.

Bob Ripley
ABS Technical Advisor

I had similar issue with cold starts only. Bob Ripley found evidence of fuel leak at weep hole on back of engine driven fuel pump during service clinic in Mobile. Pump and manifold were sent to Aircraft Accessories of OK for overhaul. Pump and manifold were installed, pressures and idle mixture set per Continental M-0. Cold starts are now back to normal with no issues. Look for fuel stains at the rear of the engine driven fuel pump. I suspect air was entering pump through failed diaphragm.

So I checked for fuel staining around pump and didn’t see anything.

The sniffle valve, when blowing from the outside panel vent, was not working. When I opened the panel I saw the hose connecting it from the sniffle valve to the vent line was disconnected. Now that doesn’t mean it wasn’t working just that it was venting inside and not outside. When I reconnected it, it worked from outside vent and could hear a click and no air would pass.

After reconnecting the first start stalled. I opened it up and saw line disconnected again. It was reconnected and modifications made so it hopefully wouldn't disconnect again. Restarted and didn’t stop at idle. Did run up and brought to idle no stall. So appears that fixed it but want to
try again with cold engine later this week.

Would venting inside cause an issue vs venting outside? I wouldn’t think so but I didn’t know what a sniffle valve was.

I also wrote down some reading of MAP and RPM at idle when rich vs lean. I saw about a 60-80 RPM rise at shutdown.

Rich - 660 RPM, 19.1 MAP
Lean - 710 RPM, 18.3 MAP
Rich - 1000RPM, 16.5 MAP
Lean - 1000RPM, 16.2 MAP

The engine ran better when lean, less sputtering. Do those MAPs look ok?

Test ran again today and died 3 times on startup. Was fine, or appeared fine, after warming up.

Dave;

I'd look for intake leaks, those MAP values are on the high side.

Mike
ABS Technical Advisor