Has anyone tried o2 sim.
07-29-2006, 08:45 PM
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Has anyone tried o2 sim. Din't know were to post this but most of the people here know what they are talking about. I'm just wondering if anyone has done this or will this work.
Quote:
Post cat O2s are designed to make sure the CATs are performing their function. As most already know, the pre CAT O2s are for A/F adjustments. The PCM wants to see a best average vector of 950mV on the pre-CAT O2s based on a comparator circuit in the PCM. On the post CATs, the PCM wants to see 450mV average based on a comparator circuit to guarantee the CATs are performing. So what happens when you remove those CATs, 950mV is read post-CAT. So how do we fix this? Easy.
I provide these instructions based on my own findings and experiments using my own tools in my own garage. If your car blows up after you perform this modification, don’t blame me.
The first mistake people often make is trying to trick the PCM by using a resistor inline on the O2 sensor. After all, the post cat O2 sensors are now outputting 0.95 volts instead of an expected 0.1 to 0.8. A resistor of value X, where value X is whatever your friends brothers dog walker’s nephew runs on his Honda with 100% success. The problem is our PCM uses a comparator circuit mega-ohm measurement device, meaning just about no matter what kind of resistance you put in, the full amount of voltage will still be seen. Remember, resistance does not drop voltage, it limits current. If the PCM were to apply a load, then resistance would inadvertently drop the voltage it saw. So this is the right idea, but the wrong method. Next mistake I’ve seen is a complicated circuit that takes the O2 sensor signals, processes them, and re-transmits them at a lower value. Geeze!!! Talk about overkill. While that will work, how about the most simple and cheap design possible!
Standard Diode from radio shack, P/N: 276-1141
The average rectifier diode is a one-way valve. It has a voltage drop when current passes through it, which is usually around 0.5 volts. There are millions of different diodes that can greatly alter that figure, but for our purposes we will use that figure because it’s EXACTLY what we need. Your cats aren’t burning off any of those unburned hydrocarbons when they’re laying in a million pieces in the trashcan, so there is plenty of oxygen present as far as the downstream O2 sensors are concerned. They’re putting out 0.95 volts. Pass through this lovely $1.29 incarnation, and whoopee! It’s 0.45 volts. What does the PCM expect? 0.45 volts is within perfect specifications.
You want to place the diode inline with the O2 sensor output. Not the 5V reference voltage, and not the heater circuit. You can find which is which by placing a voltmeter on the O2 sensor wires. The one with a varying voltage is the one you want. On most 4 wire O2s you have two matched color wires(heater circuit) and two variable colors (one is ref, other is sensor output)
Once you know which wire is your sensor output, remove the O2 Sensor/s and cut the (sensor output) wire, crimp in the diode with the silver bar facing away from the O2 sensor (toward the connector). If it’s backwards, your PCM won’t see any voltage at all. So if that happened, now you know why. Make sure you cut enough of the wire to make up for the length of the conglomeration. It’s about 1.5” if you use two crimp connectors and cut the diode leads to about 0.5” long. Bonus points if you heat-shrink this connection. Double points if you trace this/these wires back to the PCM side and do it there. If done at the PCM, the silver bar faces the PCM. All this allows positive voltage to flow from the sensor through the diode to the PCM. Re-install your O2/s.
When you’re done, the voltage drop occurs and all is good. Clear those codes and enjoy!
Quote:
Post cat O2s are designed to make sure the CATs are performing their function. As most already know, the pre CAT O2s are for A/F adjustments. The PCM wants to see a best average vector of 950mV on the pre-CAT O2s based on a comparator circuit in the PCM. On the post CATs, the PCM wants to see 450mV average based on a comparator circuit to guarantee the CATs are performing. So what happens when you remove those CATs, 950mV is read post-CAT. So how do we fix this? Easy.
I provide these instructions based on my own findings and experiments using my own tools in my own garage. If your car blows up after you perform this modification, don’t blame me.
The first mistake people often make is trying to trick the PCM by using a resistor inline on the O2 sensor. After all, the post cat O2 sensors are now outputting 0.95 volts instead of an expected 0.1 to 0.8. A resistor of value X, where value X is whatever your friends brothers dog walker’s nephew runs on his Honda with 100% success. The problem is our PCM uses a comparator circuit mega-ohm measurement device, meaning just about no matter what kind of resistance you put in, the full amount of voltage will still be seen. Remember, resistance does not drop voltage, it limits current. If the PCM were to apply a load, then resistance would inadvertently drop the voltage it saw. So this is the right idea, but the wrong method. Next mistake I’ve seen is a complicated circuit that takes the O2 sensor signals, processes them, and re-transmits them at a lower value. Geeze!!! Talk about overkill. While that will work, how about the most simple and cheap design possible!
Standard Diode from radio shack, P/N: 276-1141
The average rectifier diode is a one-way valve. It has a voltage drop when current passes through it, which is usually around 0.5 volts. There are millions of different diodes that can greatly alter that figure, but for our purposes we will use that figure because it’s EXACTLY what we need. Your cats aren’t burning off any of those unburned hydrocarbons when they’re laying in a million pieces in the trashcan, so there is plenty of oxygen present as far as the downstream O2 sensors are concerned. They’re putting out 0.95 volts. Pass through this lovely $1.29 incarnation, and whoopee! It’s 0.45 volts. What does the PCM expect? 0.45 volts is within perfect specifications.
You want to place the diode inline with the O2 sensor output. Not the 5V reference voltage, and not the heater circuit. You can find which is which by placing a voltmeter on the O2 sensor wires. The one with a varying voltage is the one you want. On most 4 wire O2s you have two matched color wires(heater circuit) and two variable colors (one is ref, other is sensor output)
Once you know which wire is your sensor output, remove the O2 Sensor/s and cut the (sensor output) wire, crimp in the diode with the silver bar facing away from the O2 sensor (toward the connector). If it’s backwards, your PCM won’t see any voltage at all. So if that happened, now you know why. Make sure you cut enough of the wire to make up for the length of the conglomeration. It’s about 1.5” if you use two crimp connectors and cut the diode leads to about 0.5” long. Bonus points if you heat-shrink this connection. Double points if you trace this/these wires back to the PCM side and do it there. If done at the PCM, the silver bar faces the PCM. All this allows positive voltage to flow from the sensor through the diode to the PCM. Re-install your O2/s.
When you’re done, the voltage drop occurs and all is good. Clear those codes and enjoy!
07-29-2006, 09:19 PM
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O2 simms are great if you dont have access to tuning and want to ditch the cats. Some people run simms with aftermarket cats as well. I'm not sure if you need to with aftermarket cats though. But it doesnt hurt anything. I used them for awhile untill I got them tuned out. I still have them. I never know when I might need them for another car again.
