EFI systems are simple to install for the most part. If you follow the instructions and take your time, you’ll have a great running system that will deliver exceptional performance in a wide range of conditions and applications. That said, not everything about installing an EFI system is cut-and-dried. There are some elements of the installation that can vary from car to car, so they require some decisions on your part as you’re putting the system together.

One of the most crucial of these decisions is how you’ll mount the oxygen sensor. This relatively small component plays a big role in the proper functioning of an EFI system. Without the oxygen sensor providing accurate feedback, the EFI system can’t tune itself. So it’s absolutely vital that you install the sensor correctly. “It’s important to avoid what I call ‘trash in and trash out,’” says Tom Kise of Holley. “Make sure that you have a clean installation with a solid platform.”

Fortunately, there are just a few specific guidelines you need to pay attention to. Follow these pro tips on how to mount an oxygen sensor correctly to get your EFI system running tip-top the very first time you turn the key.

Get Your Engine in Good Shape

Before installing an EFI system, you need to make sure your engine is in good overall condition and in proper tune. “Your engine platform has to be solid,” says Kise. “If you have ignition problems, vacuum leaks, valvetrain issues, or bad fuel, you need to correct those things before you convert over to fuel injection.”

Any of these maladies can cause the oxygen sensor to make false readings, which can force the unit to overcompensate, creating a vicious cycle that can quickly cause the engine to stop running altogether. For example, cylinder misfires from a faulty ignition system and the resulting rich mixture can wreak havoc on the functioning of an EFI system. “An engine can actually be so rich that it reads lean,” explains Kise. “If your fuel mixture is excessively rich, you’re going to have incomplete combustion. The oxygen sensor will then pick up the unburned oxygen, and in turn tell your ECU to add more fuel. And when it adds more fuel, it’s going to be even richer, so the sensor reads even leaner yet.”

Keep Outside Air Out

One of the most important goals of proper oxygen sensor mounting is to keep outside air from reaching the sensor. “You need to watch for anything that can introduce a false signal to the sensor,” says Kise. “Air leaks as small as a pinhole in the exhaust system can be detrimental to overall engine operation.”

Use the Proper Mounting Location

Mounting the oxygen sensor in the correct location is vital for proper functioning. “Proper placement of the sensor should ideally be between six to eight inches after the merge in your header collector, with at least 18 to 24 inches of exhaust pipe after the sensor,” says Kise. “That extra length of pipe is to keep atmospheric reversion from allowing ambient outside oxygen to work its way back into the pipe and give you false readings.”

It’s important to install the oxygen sensor at an upward angle so condensation doesn’t collect in it. The sensor should be installed at least ten degrees upward from horizontal. Doing so prevents incorrect readings or damage to the sensor caused by moisture that naturally finds its way into the exhaust system.

Choose the Best Mounting Method

There are several different ways to mount an oxygen sensor, all of which can work well. You should choose a method based on your particular situation. If your welding skills are good, a weld-on bung is a great way to mount the sensor. To do so, you simply drill a hole in the proper location on the header, weld the bung on, and screw the sensor into the bung.

But to use this method, the welds need to be excellent quality. Faulty welds can allow outside air to reach the sensor, which can cause incorrect oxygen readings – remember, even pinhole size openings are enough to introduce air into the system.

Click Here Now to see Holley's full line of oxygen sensor mounting solutions.

To install an oxygen sensor without welding it, there are bolt-on installation kits available. These mount a bung onto the exhaust with clamps that fasten around the collector. This method can be used permanently, or as a temporary means until you take it to a qualified welder who can weld the bung onto the header.

Whatever way you choose, make sure your sensor is screwed into some type of bung. “Don’t just drill a hole in the exhaust and stick the sensor in it,” notes Kise. “That’s just not going to support what you need.”



Clamp-on oxygen sensor bungs use a pair of clamps to mount the bung onto the collector. This can be left as a permanent installation, or you can then take the car to a shop to have the bung welded onto the collector and then leave the clamps off.

Route Your Wiring Carefully

Besides getting the position and mounting of the sensor correct, you also need to watch for anything that can damage its wiring. If the wires are compromised, they can’t communicate with the rest of the EFI system, which will cause poor operation or even complete failure of the unit. “You want to avoid high temperature sources that can burn up the wiring,” says Kise. “You also want to avoid anything that can pinch it, or movement of parts that can fray it.”

Click Here Now to see Holley's complete line of EFI systems and components.