Where to place oxygen sensor.

[joegreen]

I bought a 4 wire o2 sensor and was wondering if i should place it as close as possible to one exhaust manifold or if i should place it at the end of the y pipe where it turns into one. It seems wierd to me that it should only see one side of the engine so i would like to place it at the end of the y pipe. Would it even stay warm enough in the winter or the rain even though its heated. Thanks

[dave w]

I would place the heated O2 sensor at the end of the Y-Pipe. The heated O2 sensor will stay warm enough in the winter and rain.

Usually OBD 1 computers will be upgraded to a 3 wire heated O2 sensor, like DELPHI Part # ES10005 http://www.amazon.com/Delphi-ES10005.../dp/B001J6269C
or Bosch Part # 13077 http://www.amazon.com/gp/product/B00...C0KE08MAHH0QG0

dave w

[Hog]

I bought a 4 wire o2 sensor and was wondering if i should place it as close as possible to one exhaust manifold or if i should place it at the end of the y pipe where it turns into one. It seems wierd to me that it should only see one side of the engine so i would like to place it at the end of the y pipe. Would it even stay warm enough in the winter or the rain even though its heated. Thanks

Depending onto what vehicle you are installing this O2 sensor, it might not even matter where you put it.
An example would be a TBI engine that uses the 2 injectors. Since there is no bank to bank fueling difference, you could place the O2 sensor in the left or right exhaust manifold and the results woudl be the same.
It becomes important when installing in a vehicle that fuels on different banks. Like the Bank 1 injectiors need to have the O2 sensor that reads the Bank 1 exhaust,and the Bank 2 O2 sensor must read the exhaust from Bank 2 cylinders.

I had a 1989 Caprice with the TBI 305/200r4 4 speed auto and the 2.41 rearend. Along with pretty much idling down the freeway due to the high gearing, the car used a single O2 sensor that was located in the drivers side exhaust manifold.
AFter a new O2 sensor and tune up that car got 25-27mpg which was great for that big boat.

I agree with Dave though, placeing the O2 sensor at the end of the Y-pipe is where the sensor would see exhaust from both engine banks. This can help in case you have bank to bank variations in intake manifold design. It helps to "average out" all 8 cylinders instead of reading just 4. If space is tight, it would NOT be a sin to have it read only 1 Bank, as many OEM platforms do exactly that.
I would also weld the bung in such a manner that has the bung in the top half of the pipe. Avoid having the sensor at the bottom of the pipe where it sits in moisture/water when not running.

peace
Hog

[EagleMark]

As Hog has mentioned the angle of O2 sensor is very important. It's best position is wire pointing straight up. Worst would be straight down. This is to avoid any moisture from entering the O2 sensor which would damage it... heated or not.

[joegreen]

Yeah this is going on a 78 k20. i actually have a really good spot right after the y pipe. I bought an afs75 sensor and the appropriate pigtail so i don't have to solder the sensor to the harness.

[lionelhutz]

Different ideas for different folks. I tend to think as close to the engine as possible even if it just reads one side. Right in the collector or after the exhaust manifold. I base this on believing it closes the loop better reading the exhaust gas as soon as possible.

On another note, if you're switching from 1-wire to 4-wire then make sure to use the O2 negative signal wire that was grounded to the engine by removing it from the ground and tying it to the sensor negative output instead. The negative O2 sensor wire would likely be tan.

[EagleMark]

Just remember if you move the O2 sensor from factory position then there's a latency setting that also needs to be changed or you'll be reading the wrong part of exhaust gas, the INT/Short Term Fuel Trim will be way off.

[delcowizzid]

^^^ this LOL.I fit the sensor wherever it was stock for the code im tuning.some are in the collector measuring one side and some are in the y pipe merge makes a difference in how nice closed loop works in the codes ive played with

[lionelhutz]

That's an even better way to put it. Keep it as close to the same location as it would have been stock for the EFI system you're using.

[joegreen]

So because of latency i should stick it as close to the manifold as possible. I know what latency is but could yoy explain how that would come into play. Is it the length of the wire or are you talking about or the time it takes for the exhaust gas to reach the sensor.

[EagleMark]

Amount of time before the INT takes a reading of exhaust to make it's adjustments. If it just made an adjustment and now reads the exhaust say 300msec before the adjustment has made it to O2 sensor then it's reading the wrong part of exhaust.