twilightprotege said:
both. the problem with some piggyback puters (not all) is that the stock ecu continually wants to take control of the most important parts of the equation as much as possible. i also beleive (not sure) that the stock ecu in the 3rd gen family does not allow the piggyback to take control of the a/f at WOT (wide open throttle). perf correct me if i'm wrong...
to me it just seams much easier and more benefitial to just get an aftermarket ecu and be done with it! 
Here are some highlights of good and bad.
A standalone can control the entire spectrum of usable data. It will run your engine and control various other functions thru auxillary outputs. Sounds real nice huh? YUP but it is not that easy. It requires ALOT of time testing and calibrating so that the stock or any sensors for that matter can be interpreted and then an output to be produced that is efficient and fast enough to handle the demand of the end user. Blah Blah And more Blah
Now with todays technology there have been great improvemnts to the software some of the units use. It can "read" the stock sensor and you can input your desired output without the use of calculator. But never the less it is very difficult to tune without being on a dyno that can simulate real world conditions. . So you road tune. Works well but then you have that pesky ignition table that you try to get close but fear detonation under heavy load and Blah Blah and some more Blah.
For those that dont understand what i am doing , then read on. Standalones are a pain in the ass. I havent even touched the surface, and the level of complexity that is involved when tuning one for any vehicle. Plug and Play or not. The PNP is great only so you dont have to hack a harness for the stock inputs. Other than that it is all up to the quality of the hardware involved controlling the outputs and the ease of software use. That is why tuning rates ($) are so high. BUT they are the best when trying to squeeze the most out of any car reliably.
Now piggybacks. They work well when the proper installation method is used. Why do they work well? because the mapping is already done. The stock ecu is already running the car. A piggy will basically fine tune (manipulate or "clear the resolution path" a little) the stock sensor output or driver to whatever is needed to efficiently get the job done.
For example: many people use the MAF output as a source of A/F compensation. They will increase or decrease the output voltage from the sensor to increase or decrease the amount of fuel the ECU will give to the engine. It is done this way because it is used as a primary source of airflow feedback to the ecu. XXX amount of air is needed for YYY amount of fuel. BUT this is only good when the ecu is not receiving feedback from the O2 sensor telling it is is running lean or rich.. ( closed loop operation)
(sorry for tuning 101 here but some dont understand how it works)
So the piggy will only be good for closed loop operation when the O2 feedback is ignored by the ECU and it relies on TPS and MAF to fuel the engine from pre determined maps. One problem with the MAF signal manipulation is that you lower the load site in the ECU to one that was designated for less airflow and thus more timing lead and less fuel. Since you are now running larger injectors this is OK for the fuel department but how about when at 8psi at 50% throttle.? DETONATION
There are many drawbacks we are just highlighting some of them.
With ignition , many if not all piggybacks will manipulate the stock crank sensor.
The problem here is multifold.
First the software has to be good. Real good. Why? because it needs to be able to accurately mimic the stock signal so well as to not delay the signal back in a form the ecu cant recognize and fire the coils on time. (misfire condition) It also has to be able to advance that signal when you want to advance timing lead. If it cant do this then you are left only to delaying and retarding the signal after the piggy has had a chance to process the info and then throw it back.(Again in lamens terms for all who are not advanced gurus out there)
Lets say it does mimic the signal on the head perfectly. Great. Then you have to pray that the stock ecu takes it. WHY? You are sending the signal either earlier or later to the ecu thru the piggyback. The theory is that if you advance the notice of the signal to the ecu it will think that it is actually at a dfferent and more advanced crank angle. This will, in theory, advance the timing. There is also retard. You delay the signal thru the piggyback so that it will retard the timing. Both ways though allow the ECU to fire the coils normally under stock parameters. OR DOES IT?
See the other problem here is that the ECU gives itself time to begin with. For process latency and the fact that it will in some cases look at the cam sensor to match the signal. Gets tricky now.
The stock ECU for a while may take your manipulation and not say anything. BUT it learns. Adaptive programs learn. It will see that maybe the crank sensor is off. It will see a more consistant signal with very small variations from the cam pickup and adjust the timing back to normal.
So how do we get around some of this. Simple. For fuel and timing we go right to the source. We directly control the fuel injectors. We directly fire the coils. We directly send the car into open loop by advancing the TPS sensor voltage so that the stock ecu goes into a full "demand" mindset. I dont say load there because MAP or MAF are load and TPS is what you want. Demand from the motor to do. That for the most part will throw the car into open loop and then we can fuel away. Then we can also control the coils to fire when WE want by intercepting the stock signal or by creating our own thru the piggyback. All we need is to know the crank angle like the stock ecu does and we are set.
Well there is alot more to this stuff but it just shows why some tuners take the easy way out and use piggys. Not really for lack of tuning experience but for economic and time situations. It takes half as long to tune a basic piggyback and costless too. BUT it is only as good as its peg leg. It is still relying on stock generic mapping. It will still need to be dyno tuned to be optimal. Will you get the same gains as a standalone. Maybe. But IMHO never. Not like what a great tuner can get.
It does get alot more complex i just thought i would share some basic info with those who will by a more performance oriented auto some day and will decide to modify it. Look into the future and see what your goals are. Then see if it will be worth the hobby or the expence for modification. You may want to see what the aftermarket has to offer and see if it will work for you.
Good luck and soon there will be fun stuff for the protege out. I guarantee you that.
My 2 1/2 cents.
