If your vehicle has EFI (electronic fuel injection), then it's got an on-board computer that regulates the flow of fuel into the engine. The computer uses sensors on the manifold and the exhaust to calculate many times per second for proper fuel/air mixture settings. When running HHO in an EFI engine (especially 1996 and newer, or what we call OBD-II vehicles) the computer will adjust the fuel/air settings as you drive and bring your mileage back down. This will happen about half a tank after the hydrogen-on-demand installation.
For a comprehensive understanding, read this article and watch DVD 3 and DVD 4.
1. Disconnect the minus terminal of your battery (or better yet, unplug your ECU fuse/plug) for 15 minutes, then reconnect it.
2. With the MAP Sensor Enhancer (or EFIE) tuned to "full rich", start your engine and let it run for 2 minutes. Adjust your MAP Sensor Enhancer or EFIE to the point where the engine bucks (strong vibration), then back it off SLOWLY until it's smooth. Then kill your engine.
(If you don't have a MAP Sensor Enhancer, EFIE or other enhancer, just skip this step).
3. Restart your engine and let it run for 2 minutes, then turn it off.
4. Repeat step 3 ten (10) times.
5. Go out on a road with low traffic, drive normally and test for mileage again. If your check engine light comes back on, don't worry. That just means that your oxygen sensors are picking up a "lean mix", but hopefully this won't happen.
6. If this does happen and your mileage drops again, then:
a) Disconnect your battery (or ECU) again,
b) Unplug the oxygen sensor wire from its wiring harness,
c) Repeat steps 1-5.
7. CONDITIONAL: add an EFIE or MAP Sensor Enhancer, then repeat steps 1-5.
Several techniques of resetting the ECU are presented in the following movie (requires an Internet connection to watch):
If you don't know what type of enhancer to add, refer to the relevant chapters in the books or DVD's. If your car has a MAP sensor, use the MAP Sensor Enhancer. If your car has a MAF sensor only, and no MAP sensor, then use the EFIE (Book 2, or DVD 4).
NOTE: If the check engine light comes on when you have the oxygen sensor wire unplugged, that is normal and ok. It just means that the computer sees that this sensor is in “open loop.” In my 1999 Toyota corolla, with Map Sensor Enhancer and the oxygen sensor unplugged, I achieved 61 MPG and the car has never run better. Adding an EFIE would get rid of the pesky engine light because the oxygen sensor will not be in open loop any more.
Sensor enhancers of newer kinds are coming up from time to time - check Water4Gas.com for new offers from brilliant inventors, who specialize in the computer problem and have created brilliant solutions for you. Some of these new devices are improved EFIE's, while other are totally new and revolutionary! This is not said to minimize the importance and brilliance of EFIE and MAP Sensor Enhancer, but to tell you that if those fail or are hard to control, it's not the end of the road. The vehicle's computer is not a God from Heaven - it's just another stupid machine, and can definitely be put under control.