o-540 quitting after start

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branman
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o-540 quitting after start

Post by branman »

Trying to diagnosis an engine issue. I have a o-540 in a M5. When it is cold out (less than 20 degrees F) the engine starts up just fine (3 primes and crack the throttle) and quits about 30-60 seconds later. No backfiring or rough engine, it just quits like pulling the mixture. Mags check good and were recently overhauled. Plane is coming out of a heated hangar into the cold so there shouldn't be any ice in fuel or carb and engine is warm. I checked the tanks and no containments were found beforehand. When I start it up again after it shut down on its own and place the electric fuel pump on it runs fine. The fuel pressure does bounce between 4-5 psi on the first start but that seems normal during the warm weather when this doesn't happen. I did recently add the extended gear and 31 inch Alaska bushwheels. Another idea I had was maybe the deck angle is higher than original design and without a header tank maybe it needs the electric fuel pump to keep it happy initially if the engine pump isn't strong enough. Or maybe I'm introducing air to the fuel line by sumping the fuel sumps under the door, don't know why the cold would change that though since I've always done that. This has happened now on 2 occasions and both times it ran fine after restarting. Anyone else experience this and have any ideas?

Kirk
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Re: o-540 quitting after start

Post by Kirk »

My M5 with O540-J1A5D always has liked 5 to 6 shots of prime in cold weather, even after preheat. I have primer lines to all 6 cylinders. Have heard on the forum some aircraft don’t have primer lines to all 6 cylinders. That might make cold starts harder but I would think it would run roughly in that case…

Big tires shouldn’t make a difference since the tank is still higher than the carb and sumping fuel shouldn’t introduce air. I would try it with 5 or 6 shots of prime. Could be that the seals in the primer are wearing out too and you are not pumping enough fuel with each stroke.

Kirk

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gdflys
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Re: o-540 quitting after start

Post by gdflys »

I don't normally have the luxury of a heated hangar so I usually have to preheat. While a friend of mine was having an autopilot installed I was able to use his hangar, not heated, but had electric available so was able to use an engine cover and light bulb to preheat the engine only. That got the engine and oil up to about 40 degrees. One of the really cold days in the single digits I had a similar issue after pulling the plane out into the cold. Started right up after 6 shots of prime, ran for a short time although not quite as long as yours. It seemed to have stabilized pretty well but as I pushed the throttle open a bit to bring the RPMs up to 1000 it died. Repeated the same start up with 3 shots of prime same throttle position and it wouldn't run past the prime. Tried a few more times same result. Thought maybe I flooded it so wide open throttle nothing. Finally pulled the throttle back to nearly closed and some more prime and it caught again but as soon as I pushed the throttle open it died. So after all that I started to think that because of the extreme low temps and cold fuel it just wasn't atomizing very well and was running too lean. I tried to start it again with throttle full closed and it caught and ran at maybe 600-700 rpm continuously. I let it run like that until the engine got some more heat into it and finally was able to open the throttle without it dying. I never tried the fuel pump but that might help get more fuel in the bowl and increase the atomization and mixture somewhat maybe?
Greg Delp
1979 M-5-235C
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Dale Smith
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Re: o-540 quitting after start

Post by Dale Smith »

Seems odd that it will run for that long before it quits. I only have primer lines to 4 cylinders on mine. I run the electric fuel pump to 6 Psi then off, 4-5 shots primer, and it is normally running after 2 blades. It will run rough for a few seconds, maybe 5 at most. Then it will smooth out as the other cylinders come in. I went to extended gear and 26's, I did not have anything change.

Do you have to run the electric pump to get it started again? Is the engine driven pump getting tired?
No great story started with a good idea...

Dale Smith
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Re: o-540 quitting after start

Post by Dale Smith »

Greg,

You could be right. Your posted popped up while I was typing mine. I have never had mine die, but on cold mornings (mid 30's) my plane will stumble when you try to open the throttle.
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andy
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Re: o-540 quitting after start

Post by andy »

It might be carburetor ice forming when you move into air below freezing and the engine isn't warm enough to melt the ice. Even though the hangar is heated, you might try preheating the engine.
Andy
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