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Cheating the O2 sensor

29K views 15 replies 8 participants last post by  burganb 
#1 ·
Has anyone cheated their rear O2 sensor on a 2001 dakota 4.7l before? My dad's got my old 2001 Dakota and both front cats have gone bad on him. He wants to gut them this weekend. Anyone found out how to cheat the rear O2 sensor? I he thinks he'll need a capacitor in parrallel and (i think he said) a transitor in series to cheat it. But he wanted me to double check with you guys to see if anyone has done it.
 
#4 ·
Its not that simple on the 01+ trucks. The pcm looks for specific voltage patterns based on when it closes the heater relay. That's why a O2 sim is an actual circuit that feeds the PCM realistic looking signal that changes a set time after the heater voltage is applied.

Either try the sparkplug anti-fouler trick or have 2 new bungs welded in behind the third cat and extend the wires.
 
#6 ·
Someone did do it, and they sell them. They're called O2 sims, and they only half-ass work.

If your dad is a EE, I'm sure can figure it out, but it isn't as simple as a resistor here and a transistor there. It will need some sort of oscillator or a way to mirror the upstream signal and modify the wave form, as well as apply a voltage bias in response to the heater circuit being closed.

I can post the section from my fsm that gives the details of the signal the PCM is looking for in the morning.
 
#8 ·
This is true. Anything else will just throw a code. I have read on here of people who zip tie the downstream sensors to their frame rails and it works out okay.. I'm not too sure about this but I know I have read it on here.

Do a Google search on how to build an o2 sim..
(Example: http://www.supersoda.com/detail.php?id=00000000079)

I was wanting to build one but figured I have enough little projects at the time so it will have to wait. He should have no problem with this circuit.
 
#7 ·
the fastman dan sells the O2 simms on his site. i think i still have a pair myself that i could sell you too. i didn't end up needing them. for the time it takes to remove the cats and gut them though you could have just welded in 2 new ones. you can get the small round high flow cats on ebay for cheap. that's what i did.
 
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