Nissan Repair: cutting fuel, oxygen sensors, nissan maxima

Question
i am experimenting with a cold gasoline vaporizer that injects vaporized gasoline into the manifold on a 98 nissan maxima gxe. the goal is to use less gasoline via the injectors. 2 weeks ago i added a piggy back computer the "emanage ultimate" by greddy, when tested on the dyno we were able to cut down fuel consumption by 50% to 60% while increasing the torque at 3000rpm+ by 15%, no overheating at all!. unfortunately after driving for about one hour the gains dissapeared because the original ECU started compensating for the AFR of 19 to 20 that i was running, hence nullifying the action of the piggyback unit. since the ecu is literally " too smart" for any piggyback, i was wondering if it is possible to install smaller fuel injectors that would inject less gasoline because of their smaller size? how do i go about finding efis that fit? I was wondering if it is possible to put a control valve that would allow me to adjust the amount of fuel going to the injectors? i realize this is an out of the ordinary question, and hope you do not mind giving me your professional input. thanks a million ben

Answer
Ben,

The problem is not with the injectors.  The problem comes from the oxygen sensors.  1998 Maxima is OBD II compliant and the oxygen sensors read the exhaust and provide information to richen or lean the mixture.  Vetronix in California, a Bosch owned company, write all the code for Nissan and many other makes.  Nissan is unique and a pain to crack.  There is a place in Los Angeles, Technosquare, that will reflash Nissan computers.  I think the guys used to work at Nissan in their recent past.  Also, for about $15K they will sell you the system and the code to reprogram your computer and as many Nissan cars you can program.  Remember, in the end, if you lean out the fuel mixture too much, you will melt pistons and burn valves.  So, I hope you have a doner motor in case things get a little too hot.  The oxygen sensors are narrow band, in front of the converter, and as such they have a narrow operating range.  The one behind the converter is just looking for a signal to make sure the converter is still there.  There are simulators on the market for oxygen sensors that might address your problem on the cheap.  That is, if they just keep sending a signal to the ECM in range, with a simulator, you would get to do what you want on the top end.  But, again, I will say you might end up cooking the pistons and valves.  After you get past 17 to 1 you risk cooking parts.  Another option is an adjustable fuel pressure regulator.  Some newer cars are coming out with extreme pressure fuel injection to atomize the fuel better and that might be a way to modify your car.  But, all hoses and fittings would have to be changed to work with the higher pressure...