Throttle Questions

[FalconGuy016]

I'm pretty nubsauce when it comes to this, so bear with me please.

What factors control how much fuel is injected into the cylinder? I ask this because I have always had the general impression that the more the throttle opens up, the more gas is used, but that they are pretty much "linked". As in if the pedal is pressed an inch, the same amount of fuel is being injected regardless of the RPM level and gears. Is this true? Or is it much more complex?

I ask this because I am beginning to notice that I need to push the gas pedal in much less in 4th gear, rather than being in 5th gear at around 1400-1600 RPM. This puts the RPM at around 2500, but, it seems like I am pressing the pedal in much, much less. There is clearly more power, but am I saving gas too? This is especially true on any kind of incline at all.

Teeeeeeeach meeeeee

 

[03ghoststang]

its all linked together along with the MAF, TPS, load on the vehicle. That is why when you are in 4th the car is closer to its power band and dont require as much to keep it going...as for when you are in 5th you need a little more to keep it going cause you are out of the powerband completely.. gears will alter this

 

[4.6_02_Black_GT]

Falcon,

When you press the pedal lots of things happen but heres the general idea.

As you press down on pedal the cable opens up the throttle more, gas pedal is really a mis-nomer now. The gas pedal really opens the throttle that which allows you motor suck in more air(our engines are really big vacuum pumps). So pedal down equals more air sucked into motor.

The air being drawn into the engine is measured by the MAF(mass air flow sensor). As the engine draws more air the ECC (your stangs brain) will add more fuel to mix in the cylinders. The injectors are measured in pounds of fuel they can deliver. Most of our stangs have injectors in 19-21 pound range. The tubro and blower guys will usually upgrade to larger(in pounds) injectors so they can get more fuel to the motor.

There are many other less important sensors that control specfic aspects of engine operation. Like your oxygen sensors in the tail pipes allow the ECC to determine if its dumping to much fuel into cylinder(rich). The ECC then can reduce fuel if needed or the ECC can advance or retard your spark to return to optimuim mixture of fuel and air, and stay within emission guidelines.

Lots of other sensors are involved but I touched the main ones. Other are TPS, throttle position sensor so the ECC no how much throttle you are applying, and IAC, idle air control, PCV and other.

Hope I have anserwed your question.

 

[jstreet0204]

throttle position and fuel delivery are not directly linked.

Fuel delivery is pretty complex, and is completely controlled by the eec. The first part of the equation is determining the desired a/f ratio. This is determined by several things. Loop state, throttle state, load, and rpm.

Under closed loop the eec will adjust the fuel delivery to maintain a 14.7:1 ratio by reading inputs from the MAF then reading the results from o2 sensors. If the resulting a/f ratio is off the eec will make adjustments to the readings coming in from the MAF. These adjustsments are then stored. This is what people are refering to when you hear the term adaptive.

Under open loop the eec will get its desired a/f ratio from predefined tables. These tables are made up load values as the Y axis, and rpm values as the x axis. Each intersection of load and rpm has a defined a/f value. Now that the eec knows where to get the desired a/f ratio from it needs to get its load and rpm values. These come from the MAF and the crank position sensors. It is important to note that load, and air mass are NOT the same thing, even though they come from the same sensor. Air mass is measured directly with the MAF while load is calculated by comparing the mass of air entering the engine, to the displacement capabilites of the engine. The reason this is important, is there are some aftermarket MAF's that are calibrated to injectors. These are junk because they calibrate them by fooling the eec into thinking there is more or less air entering the engine in order to correct for the different size injectors. This completely screws up the eec's ability to calculate load.

Now back to the topic, in open loop once the eec knows its desire a/f ratio, and its load, and rpm it will calculate the fuel delivery based on the mass of air read by the MAF. Done right? Nope not yet. The eec then makes a few adjustments to the a/f ratio based on the temp of the air entering the engine, the temp of the coolant, and the adaptive adjustments that were stored during closed loop operation.

This is a simplified explanation, and some of the things I have state are out of sequence, but this will give you a basic understanding of that happens.

 

[FalconGuy016]

Thanks guys, I'm reading these posts over and over