So you're tired of your Ford getting spanked by those ricer imports and you want to shove some air down it's throat and wake it up a little. After hours of latenight Googeling pictures of 1100 HP Festivas you're ready to become notorious. Next thing you know you clicked "BUY IT NOW" on an Ebay turbo and you're waiting for the delivery van wondering what you've done.
The good news is most Ford EEC systems can be modified to handle boost. The tuning software and hardware is the same setup you would need for N/A tuning. If your car was not equipped with EFI from the factory then choose a system that has boost support built in and your life will be simpler. If you're cheap (like me) that probably means Code 59 on a GM ECM or MegaSquirt. They are described alsewhere on site. If you like/know or already own Ford tuning gear then an EEC-IV from 89-95 is the best supported option with enough flexibility to make a street tune precise enough for a daily driver.
So how do you tune an EEC that wasn't designed for boost to work with your turbo or blower ? I'll briefly describe a MAF based system first - they are the most common with Ford. The first thing you need to do is some research on how much air flow your MAF will measure. Then you need to figure out how much air flow you are going to have once your power adder is installed.
Example; a 2 liter engine inhales approx 1 liter of air every time it rotates at wide open throttle. If you are going to rev it to 6000 RPM then it's drawing 6000 liters of air in a minute. Odds are that the MAF that came on this car is sized to measure a little more than that. Look it up.
To make the math obvious let's say you plan on 14.7 lbs of boost - that will be double atmospheric pressure. You can now expect your engine to inhale 2 liters of air every revolution and that means at 6000 RPM it will draw 12000 liters of air per minute. Your stock MAF is unlikely to measure enough air for more than a few pounds of boost a top RPM. If your computer doesn't know how much air is coming in it can't calculate how much fuel to add to accomplish the air/fuel ratio you want. If your MAF will flow enough air but won't measure it accurately you can probably change just the numbers in the tune to fool the EEC into supplying the correct fuel, similar to a "matched" MAF except it will be precisely calibrated to your application. But probably you will want a larger MAF - less restriction for higher flow that is measured accurately; full of win.
Get one off of another FORD (or some other makes that uses same spec MAF) that has a larger engine or a high performance option - the F150 Lightning has the largest factory Ford MAF I believe. You can also use the newer 'slot' style MAF sensors inserted into a piece of tubing, gut the obstructions out of regular MAF for more flow or get an aftermarket performance MAF. Get the connector too you will likely need it. In all these cases you will need to change the MAF Transfer table in your tune to represent your new MAF. It's not that hard. Unmodified Ford or aftermarket MAFs have the settings available but expect to fine tune the table to get the air/fuel ratio you want. Custom MAFs will need you to figure it out yourself - I did it - it's not much more work.
In a nutshell then - to make a MAF based system work with boost - calculate your air flow - get a MAF that can measure that much air flow - change the MAF Transfer calibration numbers in your tune to match the new MAF
How about fuel ? If you shove in twice the air it is going to need at least double the fuel and probably more. Find a calculator online to get an idea of what size injectors you need to make the HP you are shooting for. Swap them in and change the numbers in the tune - Ford calls it Injector Slope. (There are three numbers - High Slope to describe the injector at normal length pulses, Low Slope to describe the injector at very short pulses and Breakpoint which tells it where switch from one value to the other. Oh ya - Battery Voltage Offset - you should change that too) There is a limit to the stock fuel pump and lines - lots of boost = lots of fuel = bigger fuel pump(s) and lines.
So now you have a turbo or a blower on your engine. You can measure the increased air flow and supply the larger fuel requirements. From there it's just straight forward tuning. Start with the injector and MAF specs from the manufacturer but be prepared to adjust them until they match what is really happening in your engine. They are correct when you get predictable linear results to the changes you are making in your tuning software. If your LOAD values are going too high at peak RPMs - beyond 180% or so - you need to adjust the range of your tuning tables. Using the example above - shoving 14.7 lbs of boost into a 2 liter engine will cause it to ingest as much air and fuel as a 4 liter engine. The EEC will likely report that as 180% LOAD. Your EEC calculations can work up to 200% LOAD, but most fuel, timing etc tables only allow you to tune to 80% or 90% LOAD on a n/a tune. You will have to adjust the Scalers to give you tuning control above 100%. If you are going beyond 180% Load you will need to go beyond moving Scalers on tables and actually fool the EEC. You want to leave some safety margin below 200%.
Proper MAF, injector and LOAD numbers should let you tune it like it is. Real airflow numbers, real fuel flow, real LOAD. If you are running out of adjustment and can't get where you need to be air/fuel wise start lying. Tell the EEC it's getting more air = more fuel. Tell the EEC it has smaller injectors than it does = more fuel. You can change the Displacement figures too. Telling it the engine is a different size can move your fuel and timing curves up and down the RPM range by changing LOAD. These are tuning tricks - they will not make small injectors or pumps or lines provide more fuel than they can flow. They can make your air/fuel/timing do what you want.
I haven't researched the speed/density systems very much. The consensus is that they are - if not more difficult - less precise. Fewer tables and controls means less street friendly manners and a sort of 'crude' tune - but it's mostly just bigger injectors and tuning to make it work. Some people adapt a different intake pressure sensor, called a MAP, into their system and adjust the tables to match it. The GM 3BAR sensor is a favorite. This is a little more advanced tuning as the readings from the MAP are used in many calculations the EEC is doing - not just the ones you want to change. Try to find someone who has such a modified tune and load it into your EEC if you can.
GET A WIDEBAND O2 sensor if you are running more than 5 lbs of boost and you want it to last a while.
Other options if you added LOW BOOST and just want it to run without knocking or bucking.
Matched MAF/Injectors. Many kit manufacturers offer MAFs that are "matched" to a larger size injector. That is they try to calibrate the voltage output of the MAF to give your stock tune the correct number to use in the fuel calculations to produce the correct mixture with the larger injectors. Some work pretty good, some don't - all are a band-aid solution for people who don't want to actually tune their vehicle. Even when they work your stock EEC is not set to provide a rich enough mixture for big boost. The more changes you make to your engine (exhaust, intake, cams, gears, etc) the more you need to really tune it.
FMU - a fuel pressure regulator that increases pressure as boost rises. To a point they will provide a richer mixture under boost. About as good as a matched MAF. Useful in a low boost engine that you do not want to actually tune.
If you are tempted to go this route - go watch Fast and Furious again - you know you want your laptop on the seat with a virtual dashboard. Now hook it all up and go get some street cred ! 8-)