It can be done, I made one, I just have to remember how! I found a web site where a guy had made one, and it's basically some parts from radio shack. I think maybe 5 or 8 dollars worth. There was a potentiometer, a really small one that had like 16 turns from like 0 ohms to 10,000 ohms, or something like that. Basically, you splice into the 5 volt reference signal and it goes to the pot, and then splice into the return signal that goes to the computer, and from there, you can "bleed" in or "bleed" out extra signal to the computer. What you are doing in effect is moving the map curve up or down by a factor of "x" with the pot. I also put in a similar one to the temp sending unit. And to get it back to stock, I wired it to a three position toggle switch. This let me set it to normal, bypassing the pot I wired in, off, so basically the computer would not recieve any signal and would be in limp mode, running real crappy for anyone wanting to steal it, or position three which was with the pots wired in sending the "adjusted" signal to the computer.
Adjustable MAP sensor
My '89 5.2 L is has a MAP sensor, and it sems to be the key to fuel injection rich / lean. Can a guy spiice the wires and make it change the air-fuel ratio? What about a dimmer switch? 
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Hey Jaamzg,
What were the results of your homemade setup? I would think for full throttle acceleration it would let you tune in for more power, but during cruising mode isn't the oxygen sensor just going to fight you on the tuning. If you richen it up with the map adjustment, the o2 sensor will see a rich condition and automatically lean it out, right?
So this would require another homemade device that would add or subtract a "gain" from the o2 input? Just wondering, cause I've also contemplated this kind of setup
Roy
What were the results of your homemade setup? I would think for full throttle acceleration it would let you tune in for more power, but during cruising mode isn't the oxygen sensor just going to fight you on the tuning. If you richen it up with the map adjustment, the o2 sensor will see a rich condition and automatically lean it out, right?
So this would require another homemade device that would add or subtract a "gain" from the o2 input? Just wondering, cause I've also contemplated this kind of setup
Roy
Well, to a degree, it seems to fight back and forth. I installed an a/f meter to the o2 sensor and that's what i watch. It does seem to have a little more power and run richer. And your right, the 02 sensor does try to compensate, but i think the map sensor and temp unit, from what i read, are the ones that affect it the most. What i've seen is the a/f meter fluctuate more between stoich (sp) rich as opposed to lean and rich, so it's running at a richer condition. What I had done, originally, was set it to run rich when off-roading and set it to normal for highway. But the set-up i have gives it plenty of off-road torque, so i just mostly run it at normal. I was also getting codes that the engine was running to cold for to long cause of the temp sender. Oh, and just to let you know, I didn't tweak it to much, because it causes more code problems, the computer thinks the sensors went out or something, so I just tweaked it a little, as if it were under a light load.
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