Hi Everyone,
Just wanted to fill you in on the results of a test we did.
We finally had a 2000 come through our shop and turn on the check engine light after the header installation. I have had an idea that I wanted to try for a while, but this was our first opportunity to test it.
On 2000 and newer Vipers, the check engine light comes on because of a heater circuit fault (the sensor does not heat up fast enough) after header installations because the sensor is farther downstream (in the collector) and is in a larger pipe. The PCM checks the resistance in this circuit a short time after the engine is started. If the value is not within the pre-programmed range, the light comes on. No big deal except the car runs too rich and pulls out spark advance, prompting you to take it in for service. Some also thought that the extending of the wires also added to the problem.
After this 2000 RT/10 turned on the light (B&B headers with the sensor **** in the collector, sensor wires extended with automotive grade wire) I took the O2 sensor out and measured the resistance in the heater circuit (the two white wires). The resistance was 5.5 ohms. I then grabbed a good used sensor and checked its resistance, also 5.5 ohms (so the extension of the wires did not change the resistance value).
The next step was to heat up both sensors and see what happens to the resistance in that circuit. Using a 1,500 heat gun, each was heated while monitoring the change. Each sensor had an increase of .1 ohm at about the same time, with a total change of 1.0 ohm over approximately 20 seconds. We now had a baseline to work from and a goal to make the ones on the car increase resistance faster.
Looking at the stock sensor, the top one in the picture below, you can see that the sensor is shrouded with only 4 small holes allowing exhaust gas in. What we decided to try was increasing the size of those holes. We set the sensor up in the drill press and drilled out the holes in the shroud (setting the stop on so we did not hit the sensor itself).
We checked the sensor resistance again, compared to the stock sensor, while heating both up. The "open" sensor resistance increased far faster than the shrouded one, (stock went from 5.5 ohm to 6.5 ohm where the opened sensor went from 5.5 ohm to 7.2 ohm in the same time). We modified the second sensor from the car and installed them for testing.
Before the change to the sensors, the car would set a light anytime the engine was started cold and allowed to idle. Now, it now does not set a light at all.
I'm fairly confident this will work for others having this problem also.
Modifying the sensor:
Compared to stock one at top:
Sean
PS.
B&B will install the O2 sensor **** in an upstream loaction by request. But, I prefer the collector loaction for a more averaged reading for the PCM.
<FONT COLOR="#ff0000" SIZE="1" FACE="Verdana, Arial">This message has been edited by Sean Roe on 08-26-2002 at 06:55 AM</font>
Just wanted to fill you in on the results of a test we did.
We finally had a 2000 come through our shop and turn on the check engine light after the header installation. I have had an idea that I wanted to try for a while, but this was our first opportunity to test it.
On 2000 and newer Vipers, the check engine light comes on because of a heater circuit fault (the sensor does not heat up fast enough) after header installations because the sensor is farther downstream (in the collector) and is in a larger pipe. The PCM checks the resistance in this circuit a short time after the engine is started. If the value is not within the pre-programmed range, the light comes on. No big deal except the car runs too rich and pulls out spark advance, prompting you to take it in for service. Some also thought that the extending of the wires also added to the problem.
After this 2000 RT/10 turned on the light (B&B headers with the sensor **** in the collector, sensor wires extended with automotive grade wire) I took the O2 sensor out and measured the resistance in the heater circuit (the two white wires). The resistance was 5.5 ohms. I then grabbed a good used sensor and checked its resistance, also 5.5 ohms (so the extension of the wires did not change the resistance value).
The next step was to heat up both sensors and see what happens to the resistance in that circuit. Using a 1,500 heat gun, each was heated while monitoring the change. Each sensor had an increase of .1 ohm at about the same time, with a total change of 1.0 ohm over approximately 20 seconds. We now had a baseline to work from and a goal to make the ones on the car increase resistance faster.
Looking at the stock sensor, the top one in the picture below, you can see that the sensor is shrouded with only 4 small holes allowing exhaust gas in. What we decided to try was increasing the size of those holes. We set the sensor up in the drill press and drilled out the holes in the shroud (setting the stop on so we did not hit the sensor itself).
We checked the sensor resistance again, compared to the stock sensor, while heating both up. The "open" sensor resistance increased far faster than the shrouded one, (stock went from 5.5 ohm to 6.5 ohm where the opened sensor went from 5.5 ohm to 7.2 ohm in the same time). We modified the second sensor from the car and installed them for testing.
Before the change to the sensors, the car would set a light anytime the engine was started cold and allowed to idle. Now, it now does not set a light at all.
I'm fairly confident this will work for others having this problem also.
Modifying the sensor:
You must be registered for see images
Compared to stock one at top:
You must be registered for see images
Sean
PS.
B&B will install the O2 sensor **** in an upstream loaction by request. But, I prefer the collector loaction for a more averaged reading for the PCM.
<FONT COLOR="#ff0000" SIZE="1" FACE="Verdana, Arial">This message has been edited by Sean Roe on 08-26-2002 at 06:55 AM</font>
