Pressing gas pedal while starting?

[Dave Botsch]

I noted that in the subaru owner's manual (I have an '05 automatic
impreza), it says that if the engine does not start, to try starting first
with the gas pedal pressed part way down and then to try with the gas
pedal pressed all the way down.

Since this is not one of the old fashioned cars that actually used to
require "priming", what exactly does pressing the gas pedal down do? Does
it send a message to the car's computer to do something special?

Thanks!

 

[Carl 1 Lucky Texan]

I noted that in the subaru owner's manual (I have an '05 automatic
impreza), it says that if the engine does not start, to try starting first
with the gas pedal pressed part way down and then to try with the gas
pedal pressed all the way down.

Since this is not one of the old fashioned cars that actually used to
require "priming", what exactly does pressing the gas pedal down do? Does
it send a message to the car's computer to do something special?

Thanks!

I'm not sure about the part-way instruction. I THINK there have been
issues in the past where that can actually confuse the ECU into
recording an incorrect 'zero' point for the TPS. maybe that's a
non-issue for 'throttle-by-wire'? I dunno
Pressing the pedal entirely to the floor will often cause newer cars to
go into a 'clear flood' mode to help move excess fuel outta the cylinders.

Carl

 

[Michael Pardee]

I noted that in the subaru owner's manual (I have an '05 automatic
impreza), it says that if the engine does not start, to try starting first
with the gas pedal pressed part way down and then to try with the gas
pedal pressed all the way down.

Since this is not one of the old fashioned cars that actually used to
require "priming", what exactly does pressing the gas pedal down do? Does
it send a message to the car's computer to do something special?

Thanks!

Exactly! Depending on how old you are you may remember carburetors. A pump
or two of the gas pedal would make the accelerator pump dump some gasoline
in the intake manifold. If the engine was flooded, holding the gas pedal
down would clear a flooded condition. When EFI came along that was so deeply
ingrained that ECU manufacturers programmed the ECU to behave the same way.
I'm not sure all will richen the mixture when the pedal is "pumped" but I
believe all will clear a flood when the pedal is held down, if only because
no more fuel is added to the increased air.

Mike

 

[Mike]

Something i notice in my 03 WRX. Say i start the car first thing in the
morn. Starts right up, head to the corner store a 1/4mile away. Turn it off,
go in, come out a few min later and go to start it. It starts harder and
when it starts the rpms are low for a sec or 2 acting like its ready to
stall before it gets to the normal idle speed. I have tried pushing the
pedal down some as i'm starting it in this situation and it fires right up.
I always thought there was no need to push the pedal down on a fuel injected
car when starting it. Does anyone elses sub do this ? If i start it in the
morn, go to work, sits all day, it starts right up without touching the gas
pedal.

 

[Carl 1 Lucky Texan]

Something i notice in my 03 WRX. Say i start the car first thing in the
morn. Starts right up, head to the corner store a 1/4mile away. Turn it off,
go in, come out a few min later and go to start it. It starts harder and
when it starts the rpms are low for a sec or 2 acting like its ready to
stall before it gets to the normal idle speed. I have tried pushing the
pedal down some as i'm starting it in this situation and it fires right up.
I always thought there was no need to push the pedal down on a fuel injected
car when starting it. Does anyone elses sub do this ? If i start it in the
morn, go to work, sits all day, it starts right up without touching the gas
pedal.

At usmb.net I HAVE read of people that experience problems when, say,
backing the car outta the garage and then going back in a few minutes to
restart it. Similar to your observation. I dunno that anything
definitive has been discovered about the issue - maybe signs of a weak
Engine Temp Sensor or something? maybe weird ECU mapping?

Carl

 

[Rick Courtright]

definitive has been discovered about the issue - maybe signs of a weak
Engine Temp Sensor or something? maybe weird ECU mapping?

Hi,

My first reaction was along similar lines:

When the car's cold (first start of the day) it needs to run a bit rich,
so no throttle opening's required. But after running a few minutes, it
MAY be the engine itself is warm enough not to need an enriched mixture,
but the sensors haven't fully warmed up yet, and are still telling the
ECU "we need a richer mixture." So opening the throttle a bit allows
more air flow, effectively overriding the ECU's instructions?

Just guessing wildly here.

Rick

 

[JD]

Something i notice in my 03 WRX. Say i start the car first thing in the
morn. Starts right up, head to the corner store a 1/4mile away. Turn it
off,
go in, come out a few min later and go to start it. It starts harder and
when it starts the rpms are low for a sec or 2 acting like its ready to
stall before it gets to the normal idle speed. I have tried pushing the
pedal down some as i'm starting it in this situation and it fires right
up.
I always thought there was no need to push the pedal down on a fuel
injected
car when starting it. Does anyone elses sub do this ? If i start it in the
morn, go to work, sits all day, it starts right up without touching the
gas
pedal.

The STi does it too; especially iof it is warm. A mechanic buddy told me
that the cold starting cycle causes a rich condition to helkp heat up the
car. However, the cold cycle shuts off and goes into running mode when the
car is about 50% warmed up. That causes the condition. If you run it for a
few more minutes until it is fully warmed up, the problem doesn't happen.

Opening the throttle partway takes the car out of the closed loop mode for
fuel (where it detects how much air is moving into the intajke manifold to
determine how much fuel to inject) and injects a bit more fuel. Pushing the
accelerator to the floor makes the ECU think it is in the WOT mode (wide
open throttle) and injects more fuel directly. So if the car has leaned out
the fuel for some reason, this makes it richer.