What do the aftermarket ECU's do that the stock one doesn't? It's fuel, timing, and boost; right? I'm curious, not doubting that a stand alone is superior, just wondering. I saw where someone mentioned individual cylinder tuning, but I don't think most people are going to run 6 wideband sensors or 6 EGT sensors and really take advantage of that. You can pull plugs, but unless you're cutting them open there's no real way to super tune each cylinder to it's max potential. Even if you were cutting them open, I'm not sure you could make quantifiable gains tuning individual cylinders one at a time at the race track. Maybe on an engine dyno, or less likely a chassis dyno, but it would extremely difficult to do on a drag strip IMO. Other than individual cylinder tuning, what features does the new stuff have that the stocker doesn't?
I would think high end boost control; boost per gear, or per RPM, or maybe even a boost ramp based on MPH. I had a car with a stand alone that would build a progressive nitrous ramp based on front wheel speed. It was awesome. A quality stand alone will do all that, right? I don't think the stock ECM will do any of that.
I don't think the stock ECM will do a timing cut / bump to build boost on a trans brake / foot brake. I would think an aftermarket stand alone would do that.
I would also think the fueling corrections based on AFR could be done much more quickly with the newer stuff. Is that right?
I saw somewhere that the XFI would shut the engine down or something if your second fuel pump didn't come on. That could be a big deal.
If the engine goes into knock, I would guess an aftermarket ECM would be able to pull timing AND reduce boost. I think the stock computer will just do timing. There is the little boost vent solenoid deal on the stock set up, but I don't think many people are running that / using that.
In terms of power production, I can see the MAF sensor going away as a potential power gain. I'm curious about how a stand alone ECM would make power beyond deleting the MAF sensor though. I've seen "data acquistion" mentioned a couple times, but I don't really know what that means. I've been through the power logger pretty thoroughly, and the only thing I really find irritating is the sample rate for MPH. It's tough to tell when the car actually leaves the line. That's a limitation of the factory VSS though, so unless the stand alone is putting a reluctor ring on the drive shaft, watching an ABS sensor, or using some other method to get a speed signal; I don't see how the stand alone solves the MPH reporting deal. That's a pretty small complaint though.
I guess I'm asking those that have a stand alone, what does it do that you like? What does it do that the chip stuff didn't do?
I ran a Pro-M EFI stand alone on my 89 Mustang and loved it. It was vastly superior to the stock ECM. The main difference was in how the computer "thought" about air and fuel. The Pro-M operates on a Lambda based fueling system, and knowing bore, stroke, and number of cylinders. The system used a MAF sensor to measure incoming air, compare it to maximum engine volume, and then calculate load / fuel needs. My Mustang was a 302, so if the MAF sensor detected 302 cubic inches of air, that was a fuel multiplier of 1. If it was half that (151 cubic inches of air) the fuel multiplier was .5. More than 302 cubic inches of air via turbo or blower, and the multiplier just went beyond one, 1.2, 1.35, etc... That was something that a KPA based table simply could not do, and it was freaking awesome because you could change stuff on the car and not have to dink with the tune. Different cam? No problem, and no laptop required. Change intake? Add a super charger? Different heads? No problem, and still no laptop required. The only changes that required re-tune were CID changes or injector changes.
That being said, the Pro-M system is the only one I've seen that uses a MAF meter. The others I've messed with have all been speed density, and operated off a KPA table, watched the wideband, and made fueling changes after the fact in an attempt to achieve a target AFR. Those systems can work awesome, but in my relatively limited experience, they are pretty limited when it comes to how the engine reacts to changes. Maybe the stuff the buick crowd is using isn't like that, I honestly don't know. For example, with a SD system, on a Buick I would be worried about adding a more efficient intercooler and having the boost go down because the intake charge is cooler, or the boost stays the same because I'm using a spring loaded waste gate but I'm moving more air now because it's cooler / denser. The MAP sensor will report the same KPA because the boost stayed the same, so I'm going to get the same fuel, which is not correct anymore because I went to a better intercooler. The wideband should pick up the lean condition, and the computer should correct for it, but I'd feel much better if the system had a way of measuring the incoming air and fueling for that, as opposed to making changes post engine via wideband.
Maybe that's nothing I should be worried about, I honestly don't know, but those are some of the concerns I'd have going to a stand alone on a Buick.
Anyone who is pretty knowledgeable on that stuff, I'd love a chance to really discuss it in detail.