The post by stang&2birds is correct, but I will try to expand as to why, as this seems to be confusing to many. Including myself up to about a month ago.
When dealing with stock Ford components there are 4 parts that need to match. If any one of these components is not aligned with the rest, then there will be fuel metering issues.
1. MAF Transfer - this is part of the computer program. It can be modified with the use of an aftermarket tuner.
2. MAS - this is the black electronics box on top of the MAF tube. These are different based on the MAF tube they were originally used on. The A9L 5.0 HO motors used a 55mm MAF tube and thus had a 55mm MAS. The 93 Cobra had a 70mm MAF tube and used a MAS specific to the 70mm MAF. So far as I know, all 70mm MAS sensors are the same.
3. MAF Tube - the major spec to be concerned with is the Inner Diameter of the tube.
4. Fuel Injectors - such as 19lb, 24lb, etc.
Air flowing through the MAF tube is sensed by the MAS.
The MAS converts that signal to a voltage, which is sent to the computer.
The computer converts the voltage signal back into an air flow, which is used for multiple calculations.
If the MAS does not match the MAF tube diameter, then the conversion of air flow to a voltage will not be accurate.
If the MAS/MAF tube do match each other, but don't match the MAF Transfer in the computer, then the conversion from voltage to air flow will not be accurate.
Notice that Injector sizes have not been mentioned to this point. Ford did not program the output of the MAF/MAS combo based on fuel injector sizes. Instead Ford made all of these changes in the computer.
If that left everyone completely confused try this FAQ I posted on my site.
Why can’t a ’93 Cobra MAS be used with an A9L Computer? (and vice-versa)
The 93 Cobra 70mm MAS sensor is not interchangeable with the 5.0HO 55mm MAS sensor. Two issues exist.
- <The slope of the air flow increase (as related to voltage gain) may not be the same on each Sensor.
- Airflow at min/max voltage may not be the same between Sensors.
Some Numbers as an Example:
At idle both MAS sensors could be at say .5v and ~30 kg/hr mass air flow.
At higher rpms both sensors could be reading the same as well, say 4.5v and 1000 kg/hr.
This would is possible because both sensors are operating on the same 0-5v range. Both motors have similar air flow capacities, so similar amounts of air would be flowing at min and max levels.
However, the rate at which the voltage changes with respect to mass air flow can vary in the middle of the 0-5v range.
At ½ throttle the Cobra meter could read 2.5v and ~200kg/hr; while the 55mm sensor could read at 2.5v and ~180kg/hr.
Some Real MAF Transfers from C&L as an Example:
The following graph illustrates how these 2 different sensors will react in the same C&L meter, with the same Red calibration tube. What is important to note is the way the 55mm sensor line (top) climbs faster, and finishes higher than the 70mm line (bottom).
Long story short…
If you have an A9L, you must use the 55mm 5.0HO MAS sensor.
If you have an X3Z, you must use the 70mm Cobra MAS sensor.
The MAS must be matched to the ECU.
What if I Use an Aftermarket Tuner?
If you do use an aftermarket tuner, then it is possible to use the cobra MAS on an A9L, or a 5.0HO MAS on an X3Z. All you need to do is make sure that the MAF Transfer you enter into your tuner is correct for the MAS/MAF you are using.
Some more Info specific to the 93 Cobra and 5.0 HO can be found here...
http://www.veryuseful.com/mustang/tech/engine/93cobra-maf-vs-stock-gt-maf.html