How To Properly Place and Install an O2 Sensor

How To Properly Place and Install an O2 Sensor

Today we’re going to talk about the oxygen
sensors so you may be thinking, well if he’s talking about an oxygen sensor, why is he
holding a carburetor? Because you’re probably taking your grocery
getter or race car and your updating it and you’re very likely going from a carburetor
to some form of a fuel injection system like our terminator throttle body that we have
here, maybe a Holley Sniper system or a multi-port kit. The carburetor works off of air velocity through
the venturi that basically creates the fuel signal to meter and atomize fuel to feed the
engine. When you’re going to fuel injection, it requires
the use of multiple sensors to give feedback to the ECU to make its fuel calculation and
to control the delivery from your fuel map to your fuel tables. One of those sensors is the oxygen sensor,
they call it an oxygen sensor for a reason because it senses the unburnt oxygen. I have a lot of people that think it senses
unburnt fuel, that’s just not the case otherwise it would be called an unburnt fuel sensor. Placement of the sensor is very important. Proper placement of the sensor should ideally
be between 6 to 8 inches after the merge in your collector with at least 18 to 24 inches
of exhaust pipe after the sensor and that extra length of pipe is to keep atmospheric
reversion from allowing ambient and outside oxygen to work it’s way back up the pipe to
give you a false reading. Holley offers a couple of different ways to
install the oxygen sensor, we have your conventional round wield in style oxygen sensor bung and
we also offer a clamp on style O2 bung that comes with a cast stainless steel mounting
bung and these are available for some different common diameter pipes that have specific radiuses
and they include high-quality T-bolt style clamps and a high-temperature gasket that
gives you a nice method of installing that O2 sensor in a secure way without the need
of welder.Now the reason we offer this is a lot of times you may not have the ability
to weld or have immediate access to a welder so you can clamp it on and this works temporarily
or even permanently if you want it for a temporary installation, you can put this on, get the
vehicle running, then take it to your muffler shop and they can take this same bung and
they can weld it or abrase it onto your pipe for you. A couple of things that you want to avoid,
and we see this quite often, is poor quality welds that introduce oxygen into the stream,
in this case, we have a burn through on the welded bung, it’s also in the wrong location,
in this installation it is basically reading off of one primary tube instead of getting
a average of 4 cylinders which would be created by this distance from the merge. Some other things you don’t want to have in
your exhaust system that wouldn’t have been bothered when you’re dealing with the carburetor
wouldn’t cause any issues is the classic hose clamp and pop can plug over a hole. Poorly fitting flanges, poor welds, oxygen
sensor installations with coat hanger, hose clamps, JB weld, lot of RTV on the flanges,
holding your exhaust together with vice grips, hose clamps, pipe clamps, we’ve seen all different
things that are going on, you want to be conscious about where you root your wiring, you want
to avoid high temperature, high heat sources that could burn up the wiring, you also want
to avoid anything that it could be pinched on or moving that can fray it. Once again make sure that you don’t mount
the oxygen sensor at the end of the exhaust pipe and please don’t do what we see here
and just drill a hole in the exhaust and stick the O2 sensor in it, that’s just not going
to support what you need. Anything that introduces a false signal to
the O2 sensor, any type of air leaks as small as a pinhole in the wrong place in the exhaust
system can be detrimental to overall engine operation, especially at idle and part throttle. When you install the O2 sensor if you are
using a Holley EFI system, depending on the type of system you have some options on the
O2 sensors. If the oxygen sensor that you get with your
system, say for a Terminator or a Terminator HP or a Dominator system has this little bag
with a warning on it, you want to read that. If you don’t program the system for the proper
sensor before you plug this in, you’re going to damage the sensor and you can really damage
it in under a minute. There are some things that cause premature
sensor failures or damage to the sensors and the common ones are going to be excessive
fuel, oil control issues or additives or chemicals that you write down to sealant that may have
been used during the assembly of the engine that just are not compatible with the oxygen
sensor. If you’re running a carburetor and you have
oil control problems, the car smokes when you start it int he morning, it’s blowing
some blue smoke sitting at idle or normal operation, you need to really correct that,
that excessive oil control issues is going to foul the sensor out and it’s going to cause
it to fail. Excessive fuel is one of the quickest ways
to kill an oxygen sensor, so what do you think is going to happen if you have a leak in the
exhaust that’s telling the ECU that it’s running lean, the ECU’s going to react accordingly
by adding more fuel, the problem is it really doesn’t need more fuel and you’re going to
wash that sensor down with fuel and it’s going to cause it to fail. The tail tell sign of a damaged O2 sensor
that’s usually caused by fouling by some sort of chemical, excessive fuel, or oil is that
the O2 sensor will all of sudden will read just dead lean and it’s because it basically
plugs it up and it can’t analyze exhaust gasses, so if all of a sudden the vehicle starts running
extremely rich and you look at your O2 sensor readings and it’s reading in the 30-35-1 range,
chances are that you fouled this sensor. If that happens you really need to figure
out what caused it to begin with, otherwise, your going to keep putting O2 sensors in and
wondering why they keep failing. It’s important to avoid what we call trash
in trash out, make sure you have a clean installation with a solid platform, make sure that your
not dealing with high-temperature issues with wiring, pinched wires, improper installations
that can cause any type of oxygen to get in the system. Cylinder misfires will also do the same thing
because you are not burning all of the oxygen. So if you have an engine that has an ignition
problem, it is going to throw everything off the rails. You want to also be conscious about excessive
fuel because a lot of people don’t realize an engine can actually be so rich that it
reads lean. Now there are guys that are scratching your
head and trying to figure out what I’m talking about, so we mentioned this thing reads unburnt
oxygen, so if your fuel mixture is excessively rich it’s really not going to burn properly,
your going to have incomplete combustion which this is going to pick up the unburnt oxygen. It, in turn, is going to tell your ECU or
engine management system to add more fuel, well what do you think is going to happen? You add more fuel, it’s even richer, it’s
going to burn less of the oxygen, it’s going to make it read leaner and it’s going to react
accordingly. Take your time during your installation, look
things over, anything that could possibly allow any oxygen into the system as small
as a pinhole on the exhaust anywhere from the combustion process to 18-24 inches after
the O2 sensor is going to cause you some problems, it may not be a major issue or it might be. Make sure that your installation is tight,
your engine platform is solid if you have ignition problems, vacuum leaks, valve train
problems, bad fuel, you need to correct those things before you convert over to fuel injection
and it’s just going to make things go a lot smoother and simplify troubleshooting, if
you do run into a problem in the future, if you correct that problem before you ever get
started. For more helpful Holley tech tips and videos,
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About the Author: Michael Flood


  1. Nice video but I would have liked some input on turbo model engines. Post turbo, pre turbo, distance , ext. I ran mine post turbo about 18 inches down and it seems to be fine but I've always wondered what a pro would say about that. I personally only have to so I know what my car is doing and running as my car is a daily. I just hate not knowing what my cars oil pressure, a/f ratio, temps, and stats are at.

  2. been waiting for decent explanation of this since replacing my exhaust with decat downpipes, now i know where to mount it 🙂 thank you !

  3. So where do I put it when I delete the cat and have the exhaust come down right near the end of the trans

  4. Wow the best informational video yet , thank you, but I was looking to find out where the male ,& female plug in on a 92 dodge Dakota 3.9 manual transmission, 2 wheel drive ,& also where is the male & female connection for a Crank shaft position sensor, on the same vehicle

  5. I installed a cam in my truck.put header but the header it self did not have a hole to put one in.but I do have 2 connected.and my truck would smell like gas.i also have code for my bad o2 sensor.what should I do?only tuning on 2 o2 sensor silverado 08

  6. I'd like your opinion on something… I have a 2002 Corvette with 82 K miles and I installed long tube headers on it and now I keep getting Error Code P1153: HO2S Insufficient Switching Bank 2 Sensor 1 and it is running pig rich. So rich in fact that it is fouling up my plugs making it hard to start and smells like gas out the tail pipe and yes I am running with 4 cats installed and yes all 4 02s are in their proper location. 

    I have ZERO exhaust leaks.

    Once it starts it runs perfect, once it is at running temp I can shut it off and it restarts perfect. I replaced the plugs and it started perfect in the AM for about 1 day (autolite double platinums.) 

    I used a laser thermometer and cold tested the temperature on the upstream o2s I got 125 on the left bank and only 62 on the right bank and about 44 on the two down stream sensors do you know what the internal heater temp should reach on their own?

    Also I am aware that on the long tube header the upstream 02s are much further down stream. So my other question is do you have any knowledge on relocating the 02s by welding up a bung in the #7 and #8 primary tube further up closer to the head (factory location on the old cast manifolds ) So I don't have to use wire extensions and so I can avoid spending a bunch of money on the other option tuning and STILL have the 02s too far down stream?

    I also realize that if I do the relocation I will NOT be getting the average reading from all 4 cylinder off each head but only a reading off the single #7 and #8 primary tubes. What would that hurt?

    I am thinking it is only a matter of time before the p1133 turns on because the plugs on bank 1 are just as fouled as they are on bank 2. Thanks in advance.

  7. I just bought a ram with aftermarket exhaust and the pipes don't meet until near the muffler at the back. Do I still put the sensor at the merge or do I put it near the headers? I don't have cats. The truck sometimes stalls and struggles to run so if you could help me it would be much appreciated.

  8. Hi,
    Regarding the optimum placement for o2 sensors. Where or what do you do when a 2 piece manifold system is replace with a 1 piece manifold (upgrade for turbo install).
    My vehicle have 2 upstream and 2 downstream. Where do the upstream ones go??

    Together (side by side) right after the new manifold? Or together after the turbo?


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