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, go to Holley.com