I just cut my cats out tonight and I was wondering if there was something I could do to make the truck run at the right air fuel mixture again and get rid of the check engine light.....I can live with my check engine light if I could just get my gas mileage back
Looking at your profile I see your truck is a 2013 model, correct? If so there are several steps that can be taken to not only eliminate the check engine light but correct any fueling issues you may have.
How is your truck actually running without the cats? Can you tell it is running really rich or is it struggling to make power because it's too lean?
Do you have an air-fuel ratio gauge? If not, now would be a good time to invest in one. That way you know exactly what the PCM is trying to do to your fueling. Hit up the racing sites and browse the classified sections or even Craigslist. I see them for sale on Craigslist quite often.
The first way would be to purchase a pair of spark plug "non-foulers" from your local auto parts. You will install the non-foulers into the exhaust in the same location as the Downstream oxygen sensors. Then you will install the oxygen sensors into the non-foulers and clear the DTC's set in the PCM. The inside diameter of the
non-foulers may not be big enough to accommodate the tip of the oxygen sensors so you may have to drill the inside diameter to fit. Sometime when I can't get the voltage on the sensors to do exactly what I want I pack the non-foulers with some steel wool and it acts like a filter. Pretty simple. It's not a fool-proof way to eliminate the check engine light but it has worked for me on so many different trucks over the years.
The next way would be to solder in a resistor on the oxygen sensor signal wire to control the return voltage to the PCM. It may take a little trial and error to get the correct wattage and ohm resistor but it works. A scan tool would be a big help so you can monitor the voltage for the Downstream oxygen sensors. I normally start with a1/4 Watt 25ohm resistor and go from there. If you want to handy like me then pick up a pair of adjustable potentiometers with an ohm range of like 1000-10,000 ohms and then you can set the voltage to whatever you want. Normally you want the downstream oxygen sensor voltage to be somewhere in the 2.75V-2.85V range. Looking at the scan tool or using a DVOM the sensor voltages will be in the 2.50V-3.50V range.
When the oxygen sensors are hot, the O2 sensor becomes a galvanic battery that typically generates a voltage signal between 0.0V - 1.0V. When the O2 sensor signal is monitored using a scan tool or a voltmeter, you will see 2.5 - 3.5V. This is because the sensor return is biased by 2.5V to prevent O2 sensor voltages from inverting and going below 0V, which would result in a possible open-loop condition that could occur under the following conditions:
Sensor contamination
O2 air inlet clogged (preventing oxygen from being drawn into the sensor via
the wiring harness)
High-load, extreme heat conditions (trailer tow up a mountain in the desert)
The next way would be to purchase a tuner that is capable of custom tuning. Setup a custom tune with your favorite tuner and have them turn off the Downstream oxygen sensors in the tune. This way the PCM ignores the Downstream oxygen sensors and does not set any DTC's for them.
