Hi again, and sorry I have been away for so long. Life gets busy and then sometimes the hobbies have to wait; that kind of sums up where I have been the last few years. I still have the toy car projects (the Lotus, a couple of Porches, and a race car) but they have been mostly on hold. Some forward progress on one Porsche and the race car (also a Porsche - originally a parts car), but that has mostly consisted of light work and parts gathering.
JustDreamin nailed the wideband thing, it is just a wideband oxygen sensor set-up with one or two oxygen sensors. The values from the wideband are the foundation for getting your air/fuel ratios correct. It is probably worth mentioning that a system that uses VW style wideband O2 sensors is probably going to offer the best long-term value. VW sensors are relatively cheap, as VW uses these wideband sensors on production cars.
My piggy-back versus reflash opinions come largely from tuning my Evo, although the experiences I have had with LS based GM PCMs has matched that experience. Also this information applies mostly to OBD2 PCMs. I have not worked with enough OBD1 PCMs to offer any strong opinions.
First, let me say piggy-backs are not inherently bad, but they work by trying to trick the PCM. Unless the piggy-back can intercept the factory O2 sensor values, or the factory O2 sensor is disabled, then any air-fuel ratio changes made by the piggy-back are likely to be undone over time by the factory PCM's internal software. The same is true of timing adjustments. While a high quality piggy-back can be tuned in such a way that it might be able to evade a PCM's auto-corrections, in practice what I have seen is that usually the PCM adjusts to the piggy-back's changes over time and takes away the boost in performance.
What follows is a really simplified version of what is going on inside an OBD2 PCM; I know I am skipping over a bunch of information, please forgive me. I am intentionally ignoring correction factors for temperature, altitude, etc. If any of what I offer here needs to be adjusted for the planned use being discussed, please let us know.
Let's start with air/fuel ratio tuning. Modern ECU/PCMs keep track of a number of internal values including things like short, medium and long term fuel trim values, and some factor for engine knock events. For fuel trims, the PCM will read the voltages being returned by the O2 senor(s), and compare that to an expected value. If the current value is higher or lower then the expected value, then the PCM's software will start adding or subtracting modification values to the various fuel trims until the car is consistently running with the expected O2 sensor voltages. In addition to this there will also be target air-fuel ratio values contained in a set of tables based on engine RPM and engine load. The load value typically is some mix of throttle position and a reading from a mass airflow sensor (MAF). Most PCMs have several tables. One of the tables usually is the "ideal" set of values that the PCM will use if everything is working perfectly. The PCM will also have other tables that include a "failsafe" set of values that should let the car run in limp mode to get home but not burn up the engine. The PCM takes the values from the fuel trims, injector size tables (and injector curves), altitude, air temperature, engine temperature, engine knock counts, etc. and comes up with a correction factor that it uses to figure out which table to use as a reference, and then how much to adjust the values from that table to calculate the actual fuel amount delivered. It then uses the feedback from the O2 sensor(s) to make further adjustments to the fuel trims.
All of this means that "tuning" the air/fuel ratio of an OBD2 PCM car ends up requiring a combination of changes. The first step is usually to dial in the scaling values, voltage and "curve" of the fuel injectors so that the engine can run with almost no adjustment to the fuel trims. Typically about 2% is considered acceptable, but with practice the injectors can frequently be dialed in to a correction of less than .5%, but getting the trims that accurate takes time and some trial and error. Once the injectors are dialed in, then the "ideal" fuel table is usually optimized for maximum performance. After that tuning may turn to the "ideal" timing table to get that optimized. Going back and forth between timing and fuel is common when trying to reach peak performance. Once the "ideal" fuel and timing is dialed in, then it may be desirable to make changes to the other timing and fueling tables (bringing them closer to the "ideal" tables) to help keep the car from losing power over time as the PCM applies self correction logic and other adjustments. Tuning timing is much like the air/fuel tuning above, but usually done after "safe" air/fuel ratios have been dialed in, with perhaps some extra fuel to help prevent engine knock under high engine loads.
The big limitation of most piggy-backs, is that they can only control the intercept values, and not the basic tables themselves, or the long term correction factors that the PCM stores. This can limit how much correction they can apply, and many times a PCM can just dial out all of the piggy-back's performance improvement over time. Resetting the PCM by unplugging it clears the long term correction factors, but also clears the "learned" adjustments for altitude, fuel quality, knock correction, injector trims, etc. While they do work, I have found re-flashing the PCM to be a better long-term solution.
I am not sure what software to use with a Ford PCM. With my Evo I used a combination of Evoscan for data logging and monitoring ODB2 data and ECUflash for building and modifying the tuning data being flashed into the ECU. This required a laptop and cable that could be plugged into the OBD2 port when I wanted to upload a new tune or do data logging. For LSx based engines HP Tuners software seems to be a reasonable option. Not cheap, but no more unreasonable than any other quality go-fast part. There are other options, but I personally do not want to venture too far from the benefits that come with being able to run factory developed ECU software.
I think a stand alone is a great option if the car is very purpose-built, but most of the people who I know that use them tend to spend more time tuning than I am willing to commit. And I probably spent almost 100 hours tuning my Evo to get things just right. But that car ran on e85 with up to 32 lbs of boot, and had a lot of engine work. Cams, head work, oversized valves and porting, intake system and exhaust modifications, upgraded fuel pump, customized ECU code for map switching (e85 and a "failsafe" 87 octane gasoline tune), etc. Quite far from OEM but it still started and ran like stock from -40 f to 110 f and everywhere in between .. without any codes, odd behavior or check engine lights.
And why am I talking abut GM LSx engines and PCMs while the current projects are both Porsche? Well, it is much more economical to add power with (and possibly blow up) a GM LSx engine on a race track than a Porsche engine .. especially if you are starting with an older water cooled Porsche (or two) that needs an engine.
I hope all of that helps!
.. in the world