When I read mpg posts claiming 12-15 mpg towing a 16,000 lb trailer, I always wonder if they're based on the actual amount of fuel used, or on the amount the truck's computer reports has been used. And if posting based on the computer's report, I wonder how the tuner interacts with the computer. Anyone getting fabulous mpg with their tuner actually checked the numbers against the amount of fuel you're buying?
As was said earlier, if there was a way to boost mpg by 20% or more, I'd expect the manufacturer would have done so and advertised the heck out of it.
First let me say that my numbers are calculated
averages for either towing or on road not towing. If I'm pulling up a steep grade I may see instant mileage ratings of 2 or 3 miles per gallon versus downhill mileages of 50 plus. I use an SCT tuner that has the capability of being left hooked up, and their are times when I do, so I can use the datalog feature to store data for download to my laptop for analysis later, but most of the time I use a ScanGuage II for monitoring the engine on the road. It's a lot more compact and easy to glance at when needed. I have not found any significant differences between either the ScanGuage or the SCT in their calculation of fuel mileages. I don't constantly do it, but I have randomly hand checked mileages and again there were no significant differences in the average numbers of either the SCT or ScanGuaue. There have been some significant differences between the onboard truck guages and either the SCT or the ScanGuage II. Part of that has to do with the fact that all of them calculate fuel mileage based on input factors such as tire revolution, engine speed, throttle position etc. My SCT allows me to tweak the on board vehicle computer with things like the "actual" tire circumference, as opposed to a default number.
As to how they react with the onboard computer. Think about this your laptop computer is a dead block until you power up. When you first power up it loads the Bios from the read only memory, and tells the processor what the parameters, are what to load and controls communication between devices. The same thing applies to your on board vehicle computer. When you turn on the key, there's a set of instructions that control just about everything on the vehicle. The SCT and others like it basically replace those instructions with a custom set of instructions. So it's not "interacting" with the computer it reprogrammed it with new instructions.
Today's electronic engines (unlike those in the old days) are easily and quickly customized for timing, fuel, air, boost even the transmission shift points. That's why I can get up to 425 hp and over 800 ftlbs of torque from an engine that came from the manufacturer rated at 325 hp with not much more than a flip of switch. All that power comes at a cost though, as my stock engine was not capable of handling that kind of power as it came from the factory. That's why I've spent close to $7K on upgrades and modifications, all of which would void any manufacturers warranty, and probably not pass very many EPA restrictions that the manufacturer had to meet. With that power comes an operator responsibility to monitor and adjust your driving as needed to keep the engine from melting down. Most people either don't want to be that involved with or are incapable of being that involved with the operation of their vehicle. They want to get in, turn the key and go. That's why they don't offer it.
