engine stoppage after startup

Today a few seconds after starting my plane, the engine mysteriously stopped, for no discernable reason. After turning on the fuel pump (I normally start without the fuel pump on) and restarting, everything was fine. All engine instruments reading normal. I taxied arouund for a while, did a runup, no problems. Flight was uneventful.
What could explain this? With almost 100hrs hobbs time, this has never happened. I have a carbeureted o-320 with one elec ign and one mag. The fuel selector was on (left tank) and both tanks had fuel. As I said, after turning on the fuel pump for the second start, the problem did not recur.

One thing I did notice, is later after the flight I was inspecting my left tank vent line and found wet fuel around a vent line fitting on the right tank. I removed the line from the fitting and inspected the flare, which was fine. I did have some fuel dribble out of the vent line when i removed it from the fitting, however. Not sure how it got in there.

Any theories as to what could cause an engine to spontaneously stop just after startup, and then run fine? It had sat for one week, and it was not very cold out, and I did give it a good dose of priming. I started without the boost pump on, but I routinely do this and have never had a problem.

You said no boost pump on start, but how about before? Did you run it to at least fill the float bowl?

yes I ran the boost pump, primed it for 4 or 5 seconds, and then stopped the boost pump and then started.

Water?

How were your samples from tanks purge?
Might be some water from condensation if your tanks were not full during that last week.
I hate intermittent problems like that. They keep you wondering what happened and if it could happen again.
Good luck in you quest.

Mine does this in cold weather, and from what I've been told, auto-fuel is the reason. No clue if that's the reason or not...doesn't make sense, but I've read it somewhere, too. I have to let the engine run at idle to warm up for 30 seconds to a minute before I advance the throttle. If I give it more than about 1,000 RPMs prior to that it'll just stop. Is that what you're experiencing?

Edit: Just to clarify, I'm using 93 Octane no-ethanol fuel. My fuel samples are clean and water free, too.

Weird... I am using Shell V-Power: 91 Octane no ethanol auto gas. I started using this fuel this summer. Today was probably the coolest day I've run the plane on this fuel, but it was still above freezing.
Interesting... I wonder why the cold weather would cause this on auto fuel? if this turns out to be the cause, I guess I should switch to avgas for the winter.

Were you full rich or ICO when you boost primed? Carb bowl was probably not full. The only really bad possibility I can think of would be a needle valve struck momentarily.

full rich during priming.

Duh...make that float valve, not needle valve. Musta cramped a gray lobe.

probably just cold engine

It is very likely that the mixture was just not quite rich enough for a cold engine.

Without any kind of choke, running on cold auto gas with a cold engine is difficult - hard to get the fuel to stay suspended and start vaporizing in the intake manifold, rather than condense on the walls.

The switch from summer gas to winter gas changes the low-temperature volatility to try to help this, but you may still have summer gas in your tank.

My bet is that it would have started again and run fine, even without the boost pump on.

Even my F.I. engine will, once in a while on a cold morning, start then die in 10-15 seconds or so if I let the rpm get too low. Then, it starts right up afterward and runs fine.

The only thing about auto fuel & winter that might make sense to me is if you have summer blend during really cold weather. it might go lean due to poor vaporization of the summer blend mogas.

FWIW, I've had similar issues with various a/c engines, both carb & FI, both mogas and avgas, in cold weather. If they have stock ignition, they are basically at best '50s-era car engines (or more accurately, '30s era-farm implements) when it comes to starting.

Charlie

prkaye said:

Weird... I am using Shell V-Power: 91 Octane no ethanol auto gas. I started using this fuel this summer. Today was probably the coolest day I've run the plane on this fuel, but it was still above freezing.
Interesting... I wonder why the cold weather would cause this on auto fuel? if this turns out to be the cause, I guess I should switch to avgas for the winter.

Click to expand...

One thing you have to keep in mind with auto fuel is that formulations change all the time and are often seasonal. It could be the fuel your using now has some different characteristics then what you had a month ago.

George

Auto fuel and engine stoppage

I remember many years ago when I was experimenting with auto fuel in my RV4, that I often had my engine quit after a few rotations. The restart was always with out incident. I went back to 100 LL and never had it happen again. I was more concerned about the auto fuels effect on the O-rings and seals than how the engine operated with it. The old style O-rings on the fuel caps expanded so much that they fell out of the grooves. As soon as I went back to 100 LL they shrunk right back to size.

On my new plane with fuel injection, during hot starts the engine almost always starts then quits, (vapor) the second start attempt is always successful. This only happens with a heat soaked engine.

Steve Barnes "The Builders Coach"

Have experienced the stoppage after start also

Had never happened before on 100LL but one cold morning the O-320 did stop rather abruptly after cranking on 93 ( no ethanol) but restarted immediately. Have been running one side with 100LL and the other mogas all summer usually tried to switch back to 100 LL on return to the pattern but may have not run all of the mogas thru.

A friend of mine purchased a 182 that I was flying regularly and got the auto fuel STC. He said the engine became noticeably more cold-blooded with the auto fuel, and flying it with him made me agree with that assessment. So for whatever magical reason makes it happen, I do believe that there is a difference in the engine's behavior between 100LL and auto fuel.

Flyfalcons said:

A friend of mine purchased a 182 that I was flying regularly and got the auto fuel STC. He said the engine became noticeably more cold-blooded with the auto fuel, and flying it with him made me agree with that assessment. So for whatever magical reason makes it happen, I do believe that there is a difference in the engine's behavior between 100LL and auto fuel.

Click to expand...

What did he mean by cold blooded? Auto fuel has a higher vapor pressure and theoretically should make it easier to start a cold engine compared to avgas.

Alcohol and fuel leak

Would be worth testing for alcohol content anyway...
http://www.eaa.org/autofuel/autogas/test_kit.asp
This is simply a Daansen 391S fuel ssample screwdriver available for around 5 bucks at most pilot shops.

Another note that's worth sharing;
I had a TIO-360 that started to be difficult to start and would quit at idle.
(Any engine behavioral changes from normal are absolutely worth investgating until you definitely know what the problem is.)
The problem...Leaky fuel primer solenoid. This darn thing sits on top of the engine and leaked fuel in that very undesireable location also.
It was leaking and as such sucked air into the system when running without priming I believe. In cruise it would barely be rich of peak with the mixture full rich. Blue staining was the way I found the problem. Cost of the part? Outrageous. Engine ran great after the fix.
I don't know a whole lot about auto fuel for airplanes but everyone knows that it can go stale just as avgas can. I recently overhauled a carb on a Honda generator and you should of seen the brown hard "calcium like" build up everywhere. The jet was completely plugged with this stuff, the float bowl coated. this was really old auto fuel though. Started first pull when I got it back together with everything cleaned out.
Good thread.

Kyle Boatright said:

What did he mean by cold blooded? Auto fuel has a higher vapor pressure and theoretically should make it easier to start a cold engine compared to avgas.

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Engine just didn't run well until it had a bit of warm up time.