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.

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

wrote in message
...
On Mon, 21 Jun 2004 13:04:33 GMT, EDR wrote:
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?

http://groups.google.co.uk/groups?q=...sson.se&rnum=1

or

http://makeashorterlink.com/?H50622F98

I asked this question last time...

Paul

On a hot start, I cool the pump body by running the battery operated
pump with the mixture closed in the Idle Cut Off position. This (on the
lycoming IO-360's Ive used it on) runs fresh "cool" fuel from the tanks,
through the pump body and back to the tank. I do this for a full minute,
then prime and start as a normal start.

Other options are to intentionally flood the engine (mildly so) and then
do a flooded start procedure (throttle wide open, mixture off and you
seem like you need 3 hands..)

Dave
wrote:

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

In article .net,
Dave S wrote:

On a hot start, I cool the pump body by running the battery operated
pump with the mixture closed in the Idle Cut Off position. This (on the
lycoming IO-360's Ive used it on) runs fresh "cool" fuel from the tanks,
through the pump body and back to the tank. I do this for a full minute,
then prime and start as a normal start.

Which aircraft do you have the engine in?
Not all fuel systems with Lycoming IO-360's have a fuel return line (at
least it is not shown on the fuel system diagram).

All the Continentals I have seen have the fuel return to either the
left main or the selected tank.

This is why the Continental procedure calls for
- Mixture idle/cutoff
- Throttle open
- Fuel pump on for 30 seconds then off

With the fuel flowing through the spider and back to the tank, the fuel
lines are purged and cooled.
Without a fuel return line, there is no means of purging the line and
cooling it. It would only pressureize the line to the pumps ablility.

Negatory, good buddy. At least not with the Bendix RSA FI controller. Fuel
isn't returned to the tanks. Some of the Continental FI schemes do that,
however.

Best regards,

Steve Robertson
N4732J 1967 Beech Musketeer Super III

Dave S wrote:

On a hot start, I cool the pump body by running the battery operated
pump with the mixture closed in the Idle Cut Off position. This (on the
lycoming IO-360's Ive used it on) runs fresh "cool" fuel from the tanks,
through the pump body and back to the tank. I do this for a full minute,
then prime and start as a normal start.

Other options are to intentionally flood the engine (mildly so) and then
do a flooded start procedure (throttle wide open, mixture off and you
seem like you need 3 hands..)

Dave
wrote:

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

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