I didn't say that ECM tuning was completely ineffective. I said you could accomplish the same thing by raising the base timing. A generic one-size-fits-all 4.9 chip is not going to do much more for you. If its custom-calibrated for specific modifications you've made, that's a different story.
Here's what I base my ECM comment on, as well as a good part of the rest of my comments. These are posts from a GM Powertrain engineer who frequents the Allantenet board. He was involved in the Allante and 4.1/4.5/4.9 engines as well as Northstar development. (Sorry, its a long post) Chips and performance mods have been a topic several times. 4.1 and 4.5 engines are essentially the same as 4.9s:
(This particular thread is about one of those "20+ hp chips on e-bay, but the discussion wanders into ECM chips in general"
"For the record...."chips" don't make power...more airflow thru the engine makes more power and the computer calibration cannot create more airflow (unless you have a turbo-charged engine and the computer is limiting boost....and/or you have a diesel....but that's another story)
If the engine has been modified with cam, heads, intake, etc....then the computer calibration will need to be modified to account for the increased airflow but the hardware mods are what is responsible for the power increase....not the calibration mods.
While there may be some engines some where that are not calibrated for the optimum performance at WOT I would say that the vast majority of them are. There is no emission nor government constraint on the fuel and spark delivered at full throttle so there is no reason, especially on a performance car engine, for the manufacturer to "hold back" on the power.
I can positively state for a fact that the Northstar engine is calibrated for maximum pwer with the factory calibration and there is no way on earth a "chip" is going to make more power. Adding or subtracting fuel or spark is not going to do anything but slow it down.
The 4.1 and 4.5 engines are just a trifle "soft" on the spark calibration to account for the fact that the engines did not have a knock sensor but no chip change is required to compensate for this. Just set the timing at the distributor up 2 or 3 degrees and run good gas and you are all set. Send the $5.00 to your favorite charity.
The item advertised on e-bay is a joke. It is just a simple resister to replace the Inlet Air Temp (IAT) or Manifold Air Temp (MAT) sensor. This will accomplish nothing except screw up the fuel calibration and make the engine drive poorly on coldstarts as it will no longer have active MAT compensation. This is an old trick that has been used for many years on a variety of fuel injection systems as a means of altering the fuel delivery curve for various reasons.
It is possible for a specific set of modifications to the engine to use the MAT substitution as a means of compensation and, in fact, it works quite well to put a variable resistance pot in place of the MAT if you are using the car for drag racing or some limited driveability use with a heavily modified engine but for an engine driven daily with no other mods the idea of gaining power by putting a resister in place of the MAT is ludicrous.
I don't think there are as many "compromises" in the factory ECM calibrations as some might imagine when the engine is operating at WOT. Many of the "chips" will turn off the knock control, for example, and then tell you you have to use only high octane gas.but you would get the same result if you used the high octane fuel with the factory calibration....to prevent detonation so the knock control system wouldn't have to retard the spark to protect the engine. The good gas is what made the power, not the "chip" that now compromises the protection of the engine. Another trick is to turn off the EGR....but the factory calibration turns off the EGR at WOT anyway. The chip without EGR will "feel" better at part throttle...but who cares about part throttle power...you are throttling the engine anyway. If you hold the throttle wide open the EGR will be disabled with the factory "chip" for free. Another trick is to delay the apply of the TCC....once again, makes the car feel better at part throttle...but, once again, the factory cal does that at WOT anyway. AC causing Hp loss, chip gets rid of it...???...the facotry cal turns off the AC compressor at WOT automatically for a short period of time so there is no need for this mod. The list goes on and on...and....there is no way the aftermarket "chips" are going to make more power.
One feature of the Northstar engine is the fact that the factory calibration runs at the optimum fueling level (actually on the rich limit of optimum) for about 30 seconds and then the calibration goes richer for protection of the piston crowns (temp) , to prevent the spark plug tips from getting too hot and inducing preignition and to protect the catalytic converter from overheating. If the engine is run at a sustained full throttle condition in about 5 minutes it will get rich enough to actually loose about 2-3 percent torque.... This feature could be eliminated in a "chip" to limit the torque loss at sustained full throttle but, you'll be buying pistons later if you run it at sustained full throttle.
This will cause some controversy, I'm sure, but the fact is that the chips sold to improve the performance of the engines rarely if ever do anything but compromise the driveability , emissions and engine protection. "
(This thread is specifically about an '89 with a 4.5)
"The 4.5 engine is like any other engine and will respond to the same modifications....unfortunately there are two obstacles....one is that there are little or no aftermarket parts available for the 4.5 engine....and, two, the engine has a speed density fuel injection system that does not react favorably to things that change the airflow thru the engine....and you must get more airflow to make more power.
Some simple things that help a little without seriously affecting the fuel injection calibration....
Get the exhaust backpressure down...go to a low restriction muffler/larger pipes/dual exhaust from the catconv back/etc.
Bump the ignition timing up several degrees. The 4.5 does not have a knock sensor so the spark calibration is on the conservative side to avoid serious damage to the engine if less than good fuel is used. If you always use premium or better the engine can benefit from an extra 3 or 4 degrees of spark. Just bump it up and drive. If you hear detonation or pinging then back it down a degree until the detonation is gone. Tune it to "top dead ping" as we laughingly call it. Nothing will be hurt if yo are reasonably carefull and use good fuel. Just always listen for detonation if yo buy unknown fuel.
Bumping up the timing is as easy as just resetting the distributor timing with a timing light.
If you really want to take the engine apart you can get the lower intake manifold and/or cylinder head ports ExtrudeHoned to smooth the surface finish and increase flow.
If the heads are off you can deck the heads about 1 mm to get more compression.
Other than having a custom cam ground or other special parts made this is the easy stuff.
If you can find someone who can reprogram the ECM chip you can find a 4.9 and plug the parts from the 4.9 into your block and have a 4.9 litre displacement instead of the 4.5 ..... nothing beats cubic inches. If you did do the 4.9 conversion (which mechanically is very doable) it will run poorly unless the ECM is reprogrammed ot recognize the extra displacement ....or....you could do a crude compensation by going to an adjustable fuel pressure regulator and bumping the pressure up 9 percent to roughly equal the 9 percent displacement increase."
"Leave the catcon in place and do the Borla or Corsa cat-back system. The cat does not hurt the power at all with an exhaust system installed.
Bump the ignition timing up a few degrees and leave the ignition system alone.
The air induction system on your engine has plenty of capacity for anything you're going to do.
Forget the chip. The factory chip has the correct fuel and spark values for maximum power. The only "soft spot" in the production chip is the spark calibration as I mentioned...it is a few degrees short of max power to give some cushion for poor fuel. You can correct this with bumping the timing up and making sure you always have good fuel. An aftermarket "performance chip" would do the same thing and require you to run good fuel anyway so just bump the timing up and save yourself some money."