O2 sensor placement does it matter?
05-09-2004, 11:22 PM
#3
0.5 BAR
Join Date: Feb 2003
Posts: 111
Re:O2 sensor placement does it matter?
Hmm, I don't think it matters that much, seeing as on the obd0 motors its pretty high up in the mani runners. My guess is unless you are running extremely hot from being rich or lean, and have it placed right at the exhaust port, the metal that the voltage is going through on the sensor won't get hot enough to where it greatly changes how much electrical charge can flow through the metals atoms.
I don't know if your talking about obd0 b's so I hope i don't thread jack. I tried asking if people using the stock ecu with an fmu or vafc, have any issues running just a single o2 sensor in their downpipe connected to both ecu pins. No one really gave a definitive answer from experience. I was shocked seeing as tons of people use vafc or fmu on obd0 jap b series.
I don't know if your talking about obd0 b's so I hope i don't thread jack. I tried asking if people using the stock ecu with an fmu or vafc, have any issues running just a single o2 sensor in their downpipe connected to both ecu pins. No one really gave a definitive answer from experience. I was shocked seeing as tons of people use vafc or fmu on obd0 jap b series.
05-10-2004, 03:01 AM
#4
3.0 BAR
Join Date: May 2003
Posts: 3,365
Re:O2 sensor placement does it matter?
One wire o2 sensors go inside the manifold (pre obd). Header o2 sensors run hot, so if you plugged your heated 3 wire unit in there, it will sense super lean conditions (until you burn it up).
3 wire o2 sensors go along the downpipe, before the cat. Assuming your car uses 3 wire o2 sensors (narrowband) then placement should be anywhere after the header/turbo assembly to the cat.. along the downpipe.
Research and you will find more info on this subject (I think I've even helped out on a thread regarding this issue in the past.
-Ryan
3 wire o2 sensors go along the downpipe, before the cat. Assuming your car uses 3 wire o2 sensors (narrowband) then placement should be anywhere after the header/turbo assembly to the cat.. along the downpipe.
Research and you will find more info on this subject (I think I've even helped out on a thread regarding this issue in the past.
-Ryan
05-11-2004, 01:10 AM
#6
0.5 BAR
Join Date: Feb 2003
Posts: 111
Re:O2 sensor placement does it matter?
If the ob0 ecu required only one o2 before, then you should be fine. The differance in exhaust gas temperature going from the runner, to high up on the dump tube should not matter THAT much, but it would take someone that new the exact temperature range that the honda engineers use to base the voltage signals off for a definate answer. Remember that once above roughly 600F degrees, the common o2 sensor primarily works off the voltage allowed through the sensor reacting to the oxygen chemically, not temperature. You should be able to reach 600 degrees in the downpipe. It just won't happen as fast on cold starts, so you will run in closed loop maybe a minute or two longer, no big deal. Most honda motors idle at 800 degrees measured in the runner, so a 200 degree loss through the turbo would be slightly generous.
Basically if your lucky enough to have a log style manifold on a single one wire o2 ecu car, then put it on the mani log for best results, but putting it high on the downpipe wouldn't be a crime to you. Just don't put it on a turbo mani that has individual runners on just a single runner, you'll just be letting your ecu see a 1/4 of the picture, but thats obvious. People put egt probes on just cylinder 3 for most honda motors, but thats just because thats the one that usually runs the hottest and it has nothing to do with your cars operations.
Basically if your lucky enough to have a log style manifold on a single one wire o2 ecu car, then put it on the mani log for best results, but putting it high on the downpipe wouldn't be a crime to you. Just don't put it on a turbo mani that has individual runners on just a single runner, you'll just be letting your ecu see a 1/4 of the picture, but thats obvious. People put egt probes on just cylinder 3 for most honda motors, but thats just because thats the one that usually runs the hottest and it has nothing to do with your cars operations.
05-11-2004, 02:30 AM
#8
3.0 BAR
Join Date: May 2003
Posts: 3,365
Re:O2 sensor placement does it matter?
To my general understanding, no o2 sensors will last when mounted under the "pressure side" of the exhaust piping. What I mean by pressure is that there is a short segment of piping that goes between the actual cylinder head ports and the turbo. Within that short area, the exhaust gasses are backed up the most (small area plus have to push the turbine). After the turbo then the exhaust gasses have a wider pipe to fill, thus less pressure.
3+ wire o2 sensors are heated, so they have power going into them, then taking a less then 1 volt signal back out. These sensors are more of a "chemical sensor" then anything else. When I get back to my computer at home in a week I will be happy to provide you with links beyond what you want to read on oxygen sensors.
Using a mix leaded gas mixture will also kill your o2 sensors (race use). Older engines were designed to use leaded gas but that effects them more in the way of the valve seals (completely different topic).
What are you exact placement options for a sensor on what you are working on?
3+ wire o2 sensors are heated, so they have power going into them, then taking a less then 1 volt signal back out. These sensors are more of a "chemical sensor" then anything else. When I get back to my computer at home in a week I will be happy to provide you with links beyond what you want to read on oxygen sensors.
Using a mix leaded gas mixture will also kill your o2 sensors (race use). Older engines were designed to use leaded gas but that effects them more in the way of the valve seals (completely different topic).
What are you exact placement options for a sensor on what you are working on?
05-11-2004, 03:29 AM
#9
0.5 BAR
Join Date: Feb 2003
Posts: 111
Re:O2 sensor placement does it matter?
The 3 wire ones are just aided in heating. Thats the only differance, theres a 12 volt wire, a ground, and the sensor feed like on a one wire. Almost every stock honda o2 is a narrow band wether its a 3 wire or single. Both 3 and 1 wire send less then 1 volt, and cross back and fourth over .45 volts. I think the VX came with a wideband though.
I would guess the pressure inside a log style manifold shouldn't be great enough to alter any temps or atomic conditions of the air/fuel ratio and or metal sensor that would go beyond the o2's operating parameters. I could be wrong though. Most o2's that people have on kit application turbo cars usually don't last long amounts of time anyways from getting plugged running rich all time at first while trying to tune or work bugs out. Regardless, I personally would stick any o2 wether its a one wire or 3 wire as close to the top of the downpipe as possible. In the case of a log style manifold I would still do it with a single wire in the downpipe just for the ease and fact it will still heat up not too shortly after a 3 wire.
I would guess the pressure inside a log style manifold shouldn't be great enough to alter any temps or atomic conditions of the air/fuel ratio and or metal sensor that would go beyond the o2's operating parameters. I could be wrong though. Most o2's that people have on kit application turbo cars usually don't last long amounts of time anyways from getting plugged running rich all time at first while trying to tune or work bugs out. Regardless, I personally would stick any o2 wether its a one wire or 3 wire as close to the top of the downpipe as possible. In the case of a log style manifold I would still do it with a single wire in the downpipe just for the ease and fact it will still heat up not too shortly after a 3 wire.
