Fuel injection explanation

I thought I understood the fuel injection process, but now I'm not so
sure.

When you cold start an IO-360, you are supposed to run the auxiliary
fuel pump with the mixture control knob pushed in until you see a rise
in fuel pressure, then shut off the pump and pull the mixture contol
knob back to shut off, and start the engine, pushing the mixture to
full rich when the engine starts.

How does the mixture control shut off the fuel? What does it control?
If the mixture is at idle cutoff, why does the engine start?

Another question, why do you start the engine with the mixture at idle
cutoff anyway? Why not start with the mixture at full rich?

Thanks, Corky Scott

In article ,
wrote:

I thought I understood the fuel injection process, but now I'm not so
sure.

When you cold start an IO-360, you are supposed to run the auxiliary
fuel pump with the mixture control knob pushed in until you see a rise
in fuel pressure, then shut off the pump and pull the mixture contol
knob back to shut off, and start the engine, pushing the mixture to
full rich when the engine starts.

Is it a Lycoming? Some have another system.

How does the mixture control shut off the fuel? What does it control?
If the mixture is at idle cutoff, why does the engine start?

Throttle controls air (air box, throttle plate), mixture controls fuel
(needle valve, spider injector controller).
Because excess fuel has been injected into the engine; enough to start
and run fro a few seconds, until the mixture lever is advanced,
allowing fuel to flow, propelled by the engine driven pump.

Another question, why do you start the engine with the mixture at idle
cutoff anyway? Why not start with the mixture at full rich?

Because the engine driven pump would flood the cylinder, creating too
rich a mixture.

Corky, cold starting the Lycoming IO-360 in my plane (1967 Beech
Musketeer) calls for mixture full rich. The boost pump is only operated
momentarily to assure that it's in working order. So I'm guessing you have
a Continental?

In any case, by running the pump until you have pressure squirts quite a
bit of fuel into the intakes just before the intake valves. In effect
flooding the engine. For most all engines, carbureted or injected, flooded
starts require mixture at cutoff. So now you crank until the engine lights
off on the fuel that is now in the intakes. Once running, enrichen the
mixture to keep it running. This is one way to start an injected engine
without a separate primer. Very primative compared to modern auto engines.
But That's what we have to deal with to get into the air!

Best regards,

Steve Robertson
N4732J

wrote:

I thought I understood the fuel injection process, but now I'm not so
sure.

When you cold start an IO-360, you are supposed to run the auxiliary
fuel pump with the mixture control knob pushed in until you see a rise
in fuel pressure, then shut off the pump and pull the mixture contol
knob back to shut off, and start the engine, pushing the mixture to
full rich when the engine starts.

How does the mixture control shut off the fuel? What does it control?
If the mixture is at idle cutoff, why does the engine start?

Another question, why do you start the engine with the mixture at idle
cutoff anyway? Why not start with the mixture at full rich?

Thanks, Corky Scott

On Mon, 21 Jun 2004 14:47:15 -0400, Steve Robertson
wrote:

Corky, cold starting the Lycoming IO-360 in my plane (1967 Beech
Musketeer) calls for mixture full rich. The boost pump is only operated
momentarily to assure that it's in working order. So I'm guessing you have
a Continental?

In any case, by running the pump until you have pressure squirts quite a
bit of fuel into the intakes just before the intake valves. In effect
flooding the engine. For most all engines, carbureted or injected, flooded
starts require mixture at cutoff. So now you crank until the engine lights
off on the fuel that is now in the intakes. Once running, enrichen the
mixture to keep it running. This is one way to start an injected engine
without a separate primer. Very primative compared to modern auto engines.
But That's what we have to deal with to get into the air!

Best regards,

Steve Robertson

Sorry I did not make it clear, we are talking about the Lycoming
IO-360 that is used in the latest Cessna 172's.

The POH is very specific about cold starting: The auxiliary fuel pump
should be turned on and the mixture control pushed in until you see a
rise in the fuel pressure, then the pump is shut off and the mixture
control returned to idle cuttoff.

The POH states that if the engine is hot, the auxiliary fuel pump is
NOT to be used.

Consequently, hot starts are extremely problematic and I can see why:
you are trying to start an engine that was shut down by pulling the
mixture control to idle cuttoff, which starves the engine for fuel,
then trying to restart it with the mixture control in exactly the same
position. Where does the engine get it's fuel to run under those
circumstances? Some people suggest that the POH should be ignored and
the fuel lines primed as per cold starts.

I'm just asking. I'm always ecstatic when I find that the engine is
cold because I know it will start right up using the cold engine start
procedure. Hot starts....

Corky Scott

Here is how I start up a Cessna 172-S (IO-360 180HP):

Cold start (oil temp below green arc): Master on, Trottle foward, mixture
foward, fuel pump for 3 sec (look for rise in fuel flow indicator), throttle
to 1/4 inch (about 1000 RPM), Ignition

Warm start (Oil temp in the green arc): Master on, Throttle foward, mixture
foward, fuel pump for 1 sec., mixture back to cut-off, Ignition. When engine
fires, smoothly but quickly retard the throttle to about the 1000 RPM range,
and quickly follow with mixture to full rich.

Hot start (Oil temp in green arc and engine shut down within last 30
minutes): Master on, Throttle foward, mixture foward, mixture back to
cut-off, Ignition. When engine fires, smoothly but quickly retard the
throttle to about the 1000 RPM range, and quickly follow with mixture to
full rich.

I've heard debate on starting the engine with full throttle (make sure you
are firmly on the brakes!). The "Warm start" is a good compromise between
the cold and hot start, and the one I use most often.

Sorry I did not make it clear, we are talking about the Lycoming
IO-360 that is used in the latest Cessna 172's.

The POH is very specific about cold starting: The auxiliary fuel pump
should be turned on and the mixture control pushed in until you see a
rise in the fuel pressure, then the pump is shut off and the mixture
control returned to idle cuttoff.

The POH states that if the engine is hot, the auxiliary fuel pump is
NOT to be used.

Consequently, hot starts are extremely problematic and I can see why:
you are trying to start an engine that was shut down by pulling the
mixture control to idle cuttoff, which starves the engine for fuel,
then trying to restart it with the mixture control in exactly the same
position. Where does the engine get it's fuel to run under those
circumstances? Some people suggest that the POH should be ignored and
the fuel lines primed as per cold starts.

I'm just asking. I'm always ecstatic when I find that the engine is
cold because I know it will start right up using the cold engine start
procedure. Hot starts....

Corky Scott

In article ,
wrote:
When you cold start an IO-360, you are supposed to run the auxiliary
fuel pump with the mixture control knob pushed in until you see a rise
in fuel pressure, then shut off the pump and pull the mixture contol
knob back to shut off, and start the engine, pushing the mixture to
full rich when the engine starts.

I get more reliable starts by moving the mixture to idle cutoff before
turning off the pump. That seems to preload the fuel pressure so that
when it catches there's fuel available. Also it takes a moment (or longer
if it's cold) for the fuel you just squirted in to vaporize, so wait a few
seconds before cranking.

Now that I've had a lot of practice (IO-540) I don't even push the mixture
full rich on start. I just push it in an inch or so to the position where
I run it on the ground. It's so lean that it stumbles above about 1500 RPM.

For hot starts I use the procedure someone else explained. No priming with
the fuel pump, just full throttle and mixture at idle cutoff, then crank
until it starts and quickly (I keep my pinky and ring finger over the ball
of the throttle and my thumb on the mixture -- crazy Comanche knob order)
pull the throttle and advance the mixture.

--
Ben Jackson

http://www.ben.com/

"Brian C." wrote in
:

Here is how I start up a Cessna 172-S (IO-360 180HP):

Cold start (oil temp below green arc): Master on, Trottle foward,
mixture foward, fuel pump for 3 sec (look for rise in fuel flow
indicator), throttle to 1/4 inch (about 1000 RPM), Ignition

Warm start (Oil temp in the green arc): Master on, Throttle foward,
mixture foward, fuel pump for 1 sec., mixture back to cut-off,
Ignition. When engine fires, smoothly but quickly retard the throttle
to about the 1000 RPM range, and quickly follow with mixture to full
rich.

Hot start (Oil temp in green arc and engine shut down within last 30
minutes): Master on, Throttle foward, mixture foward, mixture back to
cut-off,

Why mixture forward followed by mixture back to cutoff?

On Mon, 21 Jun 2004 13:04:33 GMT, EDR wrote:

Throttle controls air (air box, throttle plate), mixture controls fuel
(needle valve, spider injector controller).
Because excess fuel has been injected into the engine; enough to start
and run fro a few seconds, until the mixture lever is advanced,
allowing fuel to flow, propelled by the engine driven pump.

Thanks for the explanation EDR. My question then is: If the engine is
shut down by pulling the mixture control to idle/cutoff, where does
the engine get the fuel it needs to start again when you attempt a hot
start 15 minutes later? You aren't supposed to use the auxiliary fuel
pump and the mixture is supposed to remain at idle/cutoff during the
start in this situation.

Throttle is supposed to be advanced 1/4", but since the mixture
control is closed and the engine had stopped for lack of fuel, where
is the gas coming from to start the engine?

Thanks, Corky Scott

FWIW, the cold start procedures in your POH differ from the procedure in mine.
However, it sounds like the hot start procedures are the same.

As to your question about where the engine gets its fuel to hot start ... Even
though you killed the engine with the mixture control, a bit of fuel will still
leak out of the injector lines and into the intake after the engine is shut
down. That is usually *more* than enough to start and run the engine for a few
seconds. In fact it's enough fuel that the engine will flood if it's hot and
the mixture is set rich.

Hot starts on FI engines are problematic. On mine, I almost always (but not
always) get it to light off and run using the POH procedures (throttle at fast
idle, mixture cut off, no boost pump, crank until start, enrichen mixture).
However, some of my Musketeer bretheren with the same Lyc. IO-360 have better
luck with intentionally flooding the hot engine using the boost pump and
mixture control before starting. Then they use the procedure for a flooded
engine. I have once or twice resorted to this when I couldn't get a hot start
with the normal POH procedure.

Also FWIW, I really don't like fuel injection on airplane engines. Sure it's
great not to have to worry about carb heat. But instead I worry about hot
starts and plugged injectors. As far as the "advantage" of quicker throttle
response for FI, I say big deal. Your supposed to throttle up gently on all
engines, so I just don't see FI as an advantage here. Still, the Lyc IO-360
seems to be a pretty good engine and it and I have come to an understanding
about hot starts.

Best regards,

Steve Robertson
N4732J 1967 Musketeer Super III

wrote:



The POH is very specific about cold starting: The auxiliary fuel pump
should be turned on and the mixture control pushed in until you see a
rise in the fuel pressure, then the pump is shut off and the mixture
control returned to idle cuttoff.

The POH states that if the engine is hot, the auxiliary fuel pump is
NOT to be used.

Consequently, hot starts are extremely problematic and I can see why:
you are trying to start an engine that was shut down by pulling the
mixture control to idle cuttoff, which starves the engine for fuel,
then trying to restart it with the mixture control in exactly the same
position. Where does the engine get it's fuel to run under those
circumstances? Some people suggest that the POH should be ignored and
the fuel lines primed as per cold starts.

I'm just asking. I'm always ecstatic when I find that the engine is
cold because I know it will start right up using the cold engine start
procedure. Hot starts....

Corky Scott

On Tue, 22 Jun 2004 08:56:08 -0400, Steve Robertson
wrote:

Also FWIW, I really don't like fuel injection on airplane engines. Sure it's
great not to have to worry about carb heat. But instead I worry about hot
starts and plugged injectors. As far as the "advantage" of quicker throttle
response for FI, I say big deal. Your supposed to throttle up gently on all
engines, so I just don't see FI as an advantage here. Still, the Lyc IO-360
seems to be a pretty good engine and it and I have come to an understanding
about hot starts.

I doubt that the throttle response from carburator to fuel injection
would be discernable. Carburators have a system called the
accelerator pump which literally injects fuel directly into the
venturi when the throttle is snapped open. It's a one time shot to
prevent stumble when you stamp on the accelerator pedal. After that,
the full throttle fuel enrichment system takes over, as long as you
are demanding full throttle, or above normal throttle.

Fuel injection, the type that has individual injectors for each
cylinder, can't do that. The amount of fuel injected has to respond
according to how it's been designed to operate. In todays cars, the
injectors are designed to be able to inject the proper amount of fuel
according to a number of parameters and sensors, all controlled by a
computer. But unless you're flying behind a FADEC system, the fuel
injection systems for Lycoming and Continental are not that
sophisticated.

With the non computer controlled injection systems being used in
aviation right now, the only advantage you get over carburators is not
much worry about carb ice and somewhat better fuel distribution per
cylinder which may permit you to use mixture settings on the lean side
of peak.

Hot starting is not one of the advantages.

Getting a much better fuel burn is not really going to happen until
computers get involved with controlling the injectors.

When you consider that most of the life of the engine is spent
cruising at the leanest safe settings, both carburated engines and
fuel injected engines end up being fairly close together in fuel burn
because both are optimized for that operation.

That's as I understand things.

I did not know that Lycoming counted on a certain amount of post
engine shut down bleed through from the injectors to allow a hot non
primed restart. With a carburator, hot starts are (or should be) non
events as the moment the engine is turning it's sucking fuel from the
carburator.

Corky Scott