Fuel injection explanation

[[email protected]]

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

[EDR]

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.

[Steve Robertson]

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

[[email protected]]

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

[Brian C.]

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

[Ben Jackson]

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/

[Andrew Sarangan]

"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?

[[email protected]]

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

[Steve Robertson]

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

[[email protected]]

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

[Paul Sengupta]

> 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=paul+sengupta+idle+cut-off+group:rec.aviation.piloting&hl=en&lr=&ie=UTF-8&group=rec.aviation.piloting&selm=bmm3vt%24k8%241%40newstree.wise.edt.ericsson. se&rnum=1

or

http://makeashorterlink.com/?H50622F98

I asked this question last time...

Paul

[Dave S]

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

[G.R. Patterson III]

Steve Robertson wrote:
>
> 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.

Interesting. Since the reason usually advanced for using the mixture to shut down is
that the engine will be starved for fuel and consequently will not fire if the prop
is moved on the ground, it seems that fuel injection is less safe than carburetion.
At least in this regard.

George Patterson
None of us is as dumb as all of us.

[EDR]

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.

[Paul Sengupta]

"G.R. Patterson III" > wrote in message
...
>
> Steve Robertson wrote:
> >
> > 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.
>
> Interesting. Since the reason usually advanced for using the mixture to
shut down is
> that the engine will be starved for fuel and consequently will not fire if
the prop
> is moved on the ground, it seems that fuel injection is less safe than
carburetion.
> At least in this regard.

I asked an examiner this question...he said it was correct, but that
it only takes a few hours for all the fuel to evaporate so it's likely
to be fine after that!

Paul

[Steve Robertson]

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

[Robert M. Gary]

Steve Robertson > wrote in message >...
> 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.

That's why God invented engine monitors. I can't imagine owning an
injected engine without an engine monitor.

-Robert, IO-360-A3B6 Mooney driver

[Brian C.]

> > 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?
>
>
>

When the plane was shut down last, it was accomplished by pulling the
mixture to cutoff and starving the engine of gas. By pushing the mixture
full foward for the hot start, The fuel in the lines primes the engine
without the need for additional priming with the aux. fuel pump. The engine
catches almost as soon as you engage the starter with a hot start.

[EDR]

> Steve Robertson wrote:
> > 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.

In article >, G.R. Patterson III
> wrote:
> Interesting. Since the reason usually advanced for using the mixture to shut
> down is
> that the engine will be starved for fuel and consequently will not fire if
> the prop
> is moved on the ground, it seems that fuel injection is less safe than
> carburetion.
> At least in this regard.

A better answer might be that retarding the mixture creates too lean a
mixture for ignition.
For example, if the engine does not quit with the mixture retarded
(chugs, diesels), you can then advance the throttle and create a leaner
mixture.