This is a question for older systems that use only one O2 sensor:

Since voltage remains the same in a parallel circuit, what would be the effect(s) of splitting the signal and running two sensors?

 

I assume you want to do this to run true duals. My advice is not to mess with it, run false duals instead. Or run an X-pipe and put the sensor in the middle of it.

If you run 2 sensors in parallel the voltage output will be the same as the highest output, so if one bank runs slightly rich or lean, the output is not the average voltage, but rather the highest voltage. Also the signal output from the one sensor can actually damage the other sensor, much as probing them with an ohmmeter can damage them.

True duals are not going to gain you a significant amount of power over a well designed single if you are using the truck as an everyday driver. The power gains resulting from dual exhausts are best noticed on the racetrack in the form of quarter mile time. In an of themselves they aren't going to make a lot of difference unless modifications to the engine and intake are also made. They certainly won't gain you enough to offset the risk of damaging the computer from false O2 signals. If you don't want to run false duals or an X-pipe setup, consider and aftermarket computer that supports multiple sensors.

 

Thanks for the advice Bear River.

The truck is already a dual setup. It's an auction truck, and the previous owner modified the exhaust by cutting the cats and running duals. He stopped just short of replacing the stock crossover pipe and the stock manifolds. They are pretty rusty and starting to leak, so I have decided to replace them with longtube headers into an x-pipe.

My concern was with the placement of the O2 sensor. I had already planned to install it in the middle of the x-pipe - just like you suggested - but I have read some negative feedback about placing it at a greater distance than the original location. However, after reading some more, and asking some ford race-car builders, and ford mechanics I know, I am confident the truck will run fine with the sensor being in it's planned location at the junction of the x-pipe. Even if I run into problems with that setup, I can always change it - I rather enjoy the trial-and-error process.

I was at drill (Army National Guard) today doing my annual health assessment - boring - and I had some time to actually think about the idea of running two sensors into one input, and I quickly came to the same conclusion that you described. I also posted this in the electrical forum, and one of the moderators - I forget his name at the moment - replied with the exact same conclusion.

Thanks for taking the time to reply.

 

The only real problem with placing it further away from the stock location is it can take longer for the sensor to heat up and read right. No biggie.

 

kens64,

Right now, the sensor is installed in a small tube that bridges the two pipes coming out of the manifolds. My wrench buddies told me that the new location will actually pick up a better pulse than where it is now, and that it might take a few more seconds to heat up if anything - like you said, no biggie.

The consensus from all the folks I talked to is that the truck will run fine with the setup I have planned, and that it'll be a significant improvement from what I have now.

 

Voltages are not always the same in a parallel circuit.

The oxygen sensor developes its own voltage which is a pulsating voltage. The computer could not read two signals coming in to the same input.

Sensor voltages are developed from the heat of the exhaust. That is why they are located as far up in the system as possible. The more heat, the more voltage, and the better they work. Locating the sensors in a colder area would diminish the ability of the sensor to do its job, and engine efficiency would suffer. If too cold, the system would not go closed loop.

False duals are worthless except for looks. jd

 

This is from Wikipedia, which is just a simple definition of a parallel circuit:

"A parallel circuit is a different path for current through each of its components. A parallel circuit provides the same voltage across all its components."

If you were to run a 5 volt charge to two sensors from one source, both would receive 5 volts. The problem lies in the voltage returned - it would be the sum of both sensors. The computer would read them just fine, but the combined signal would give a "false" reading - not the true A/F ratio of the engine's output.

O2 sensor voltages are not developed from the heat of the exhaust; they are caused by an electrochemical reaction that measures the amount of oxygen ions in the exhaust. The heating of the sensor merely allows this reaction to occur. Once the sensor reaches operating temperature (approx. 300 deg C), it is effective as long as it remains at, or above, that temp - which is well below what exhaust temp's are at any point in the system that anyone would even consider installing an A/F affecting sensor.

As was mentioned earlier, the most obvious issue is with how much time it takes for the exhaust to warm up enough for the computer to enter CL mode - which, as also aforementioned, is a non-issue.

The only possible driveability-affecting issue with moving an O2 sensor further from the stock position would be with the time-delay in response to the exhaust pulse. The severity of this effect may be anything from so miniscule that only a professional racing team would even care, or causing noticeable engine performance problems.

As far as false-duals go, I agree, true duals flow better - though I don't know why anyone would think that a false-dual would look cooler.