Originally Posted by downwardspiral
Can we get into more detail with this stuff
.. I don't know much about fuel injection systems. So a MAF and a MAP are interchangeable? In other words, with an SRT6 MAP, all you would have to do is calibrate the ecu or modify the signal from the MAP to read the correct voltage in order modify the fuel curve into a safe range?
MAF is a Mass Air Flow sensor. It measures the amount of air going into the engine by heating an element that is in the airstream and registering the amount of current required to keep it at a constant temperature. To make it work, the ECU must have the following information: MAF airway size, incoming air temp, throttle body size, throttle position, engine load and engine RPM. It requires all these parameters because it interpolates the amount of air entering the engine but teh same voltage will mean somethign completely different if the aforementioned values aren't the same. For instance, you're accelerating up a hill with the cruise on vs WOT start from a dead stop. the voltage coming from the MAF have the potential to be the same but there is way more load on the engine from a dead stop than just keeping speed going up a hill and as a result, the engine could be drawing in the same amount of air but all the other things would be different.
MAP is Manifold Absolute Pressure. It is measuring the pressure of the air intake tract whether it be vacuum or boost. This will read differently depending on your altitude and adjust accordingly for air density. It's not perfect but it is more accurate than MAF when measuring the actual pressure going into the cylinders. It is a stand alone sensor in that to get its' specific value, it does not require the use of other sensors on the car. With this, the ECU does all the leg work for what part of the fuel table it should be in.
Now the reason that this car is such a pain to do FI on has nothing to do with the fact that it uses a MAF or a MAP. The NA actually has a MAP sensor to measure vacuum but the second it sees boost, it knows it's a no-no and doesn't know how to respond. The other thing is that as you go from vacuum to boost, the SRT ECU knows that it is approaching this threshold and it knows that shortly, it will either be back in boost or stay in vacuum. The NA ECU reads lack of vacuum as lower engine load and also lower fuel requirement - a bad match because it will cause a lean condition if it is actually in boost.
Hope this helps those interested.