Cheating the O2 sensor - Dodge Durango Forum and Dodge Dakota Forums
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post #1 of Old 04-14-2010, 09:31 PM Thread Starter
burganb
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Question Cheating the O2 sensor

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.



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post #2 of Old 04-14-2010, 10:41 PM
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Quote:
Originally Posted by burganb View Post
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.
How many O2 sensors are on the truck?
How many cats?
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post #3 of Old 04-15-2010, 12:48 AM
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"My dad's got my old 2001 Dakota and both front cats have gone bad on him. He wants to gut them this weekend"

Ain't nothing like good ole pops to guide his son and lead by example on how to cheat...

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post #4 of Old 04-15-2010, 02:04 AM
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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.
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post #5 of Old 04-15-2010, 03:38 AM Thread Starter
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So i'm hearing that noone's done it...

that's alright I'm sure he'll be able to figure it out considering he is a Mechanical Engineer with a background in Elitrical systems and electronic...



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post #6 of Old 04-15-2010, 03:57 AM
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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.
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post #7 of Old 04-15-2010, 02:23 PM
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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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post #8 of Old 04-15-2010, 02:40 PM
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Quote:
Originally Posted by vortmax View Post
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.
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.
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post #9 of Old 04-16-2010, 04:22 PM Thread Starter
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He says y'all are think too much with this. I have no comment on that matter. He might not even do it this weekend on the account of chance of rain



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post #10 of Old 04-16-2010, 04:27 PM Thread Starter
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Originally Posted by Duner View Post
How many O2 sensors are on the truck?
How many cats?
Three cats
two small ones before the pipes go to one
one large one just before the muffler.

I thought you had a 4.7 and would know that, but you probably have a completely custom exhaust since you're running a turbo



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post #11 of Old 04-16-2010, 04:39 PM
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2001 FSM: 25 - 16 EMISSIONS CONTROL

Quote:
OXYGEN SENSOR HEATER MONITOR
If there is an oxygen sensor (O2S) shorted to voltage DTC, as well as a O2S heater DTC, the O2S
fault MUST be repaired first. Before checking the O2S fault, verify that the heater circuit is operating correctly.
Effective control of exhaust emissions is achieved by an oxygen feedback system. The most important element of the feedback system is the O2S. The O2S is located in the exhaust path. Once it reaches operating temperature 300 to 350C (572 to 662F), the sensor generates a voltage that is inversely proportional to the amount of oxygen in the exhaust. The information obtained by the sensor is used to calculate the fuel injector pulse width. This maintains a 14.7 to 1 Air Fuel (A/F) ratio. At this mixture ratio, the catalyst works best to remove hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxide (NOx) from the exhaust.
The voltage readings taken from the O2S sensor are very temperature sensitive. The readings are not accurate below 300C. Heating of the O2S sensor is done to allow the engine controller to shift to closed loop control as soon as possible. The heating element used to heat the O2S sensor must be tested to ensure that it is heating the sensor properly. The O2S sensor circuit is monitored for a drop in voltage. The sensor output is used to test the heater by isolating the effect of the heater element on the O2S sensor output voltage from the other effects.
Go ahead and try to add a resistor. See what happens.


Quote:
Originally Posted by Jasonb61 View Post
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.
That seemed to work for the old Federal emissions trucks, but the 2001+ with the precats are much touchier. They are actually touchy enough to like particular brands of sensors...Bosch's don't work well because their tolerances are slightly too loose for what the computer wants to see.


this may be of interest too:

14 - 48 FUEL INJECTION
Quote:
Upstream Sensors - Engine Equipped With 4 Sensors: Two upstream sensors are used (1/1 and 2/1). The 1/1 sensor is the first sensor to receive exhaust gases from the #1 cylinder. They provide an input voltage to the PCM. The input tells the PCM the oxygen content of the exhaust gas. The PCM uses this information to fine tune fuel delivery to maintain the correct oxygen content at the downstream oxygen sensors. The PCM will change the air/fuel ratio until the upstream sensors input a voltage that the PCM has determined will make the downstream sensors output (oxygen content) correct.
The upstream oxygen sensors also provide an input to determine mini-catalyst efficiency. Main catalytic convertor efficiency is not calculated with this package. Downstream Sensors - Engine Equipped With 4 Sensors: Two downstream sensors are used (1/2 and 2/2). The downstream sensors are used to determine the correct air-fuel ratio. As the oxygen content changes at the downstream sensor, the PCM calculates how much air-fuel ratio change is required. The PCM then looks at the upstream oxygen sensor voltage, and changes fuel delivery until the upstream sensor voltage changes enough to correct the downstream sensor voltage (oxygen content). The downstream oxygen sensors also provide an input to determine mini-catalyst efficiency. Main catalytic convertor efficiency is not calculated with this package.

Downstream Sensors - Engine Equipped With 4 Sensors: Two downstream sensors are used (1/2 and 2/2). The downstream sensors are used to determine the correct air-fuel ratio. As the oxygen content changes at the downstream sensor, the PCM calculates how much air-fuel ratio change is required. The PCM then looks at the upstream oxygen sensor voltage, and changes fuel delivery until the upstream sensor voltage changes enough to correct the downstream sensor voltage (oxygen content).
The downstream oxygen sensors also provide an input to determine mini-catalyst efficiency. Main catalytic convertor efficiency is not calculated with this package.
If I read that right, the PCM does use input from the downstream sensors to set fuel trim as well. It's kind of nebulous in it's description, but enough persuade me to let the sensors see actual exhaust flow.

Last edited by vortmax; 04-16-2010 at 04:50 PM.
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post #12 of Old 04-16-2010, 05:30 PM
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cant say for 01+, my 00 n 98 the last 02 sensors that monitor the cats i pulled n put in the frame then plugged the holes, no CEL, no cats
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post #13 of Old 04-19-2010, 02:02 PM
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i'm not sure what would happen with NO cats at all, but i know at least on mine i have the 3rd cat removed and the sensor still plugged into the same spot and no codes.


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post #14 of Old 04-19-2010, 02:10 PM
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Quote:
Originally Posted by burganb View Post
Three cats
two small ones before the pipes go to one
one large one just before the muffler.

I thought you had a 4.7 and would know that, but you probably have a completely custom exhaust since you're running a turbo
My 4.7 had no pre-cats and only a single cat from the factory. With that single cat, it just had one O2 before the cat and one after.

Whichever O2 sensor in your dad's truck the PCM reads for fuel trims will need to stay in the pipe.
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post #15 of Old 04-19-2010, 04:23 PM
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Quote:
Originally Posted by Duner View Post
My 4.7 had no pre-cats and only a single cat from the factory.
lucky...my 4.7 has cali emissions...3 cats 4 o2s...from my understanding the o2 in the rear cat just monitors cat function

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