Ron Kanna wrote: Thanks, I have been considering doing that.
But I was thinking, I know that can be dangerous!! Why would it get 16% worse mileage if the computer was compensating? Wouldn't you think it would stay the same but not get worse??
The thing to remember or be mindful of is that by modifying the system, the overseer of that system will see a different data stream than it is programmed to consider as “normal,” so if the result is different than expected, you have to be prepared to rectify/alter it as well.
The groove modifies the air going in, which changes what the computer looks at coming out; this means you have to take into consideration all sides of the equation it looks at. That gives you a bunch of options - MAF/MAP alterations, o2 alterations, both and neither, and possibly others. Only you can determine what works best for your vehicle.
Conservatively, Carlos’ suggestion to consider changing the o2 sensor(s) and doing a re-learn drive cycle is valid.
Another possibility is that the truck needs a solid and complete tune-up (depending on how well maintained it was to begin with) before you start to see mileage gains. New spark plugs/wires, air filter, MAF cleaning- general basic maintenance- may be more effective than an EFIE or new o2 sensor(s). Maybe your exhaust system is leaky, maybe the EGR valve needs cleaning/repair, maybe the intake and exhaust valves are sticky...
The Groove can help, but a number of other things can elevate it to its highest potential: compression/blowby issues, general conditioning, sensor issues, valvetrain, all of the above...lots of possible problems/issues to be ruled out in this case.
You’ve come this far: it’s time to dig deeper to point you in the right direction