Oxygen sensor location for EFI

65 Mustang

Well-known member
Hello Everyone. I am in the process of installing the Holley Autolite 1100 efi system on my ‘65 mustang. Looking for the best spot to weld in the O2 sensor bung. Holley says to install shortly after the collection of all cylinders. It also mentions to have it higher than a 10 degree angle from horizontal to avoid water and moisture. I marked the area in the photo where I am thinking of installing it. The pipe at that point pretty much runs vertical. This means the sensor will go in perpendicular. I believe the 10 degree angle only applies when the exhaust pipe is horizontal. I don’t think water or moisture will be an issue if the sensor is placed in the marked position. Before I start welding, though, I thought I would check in with you guys. I’ve seen people weld it further downstream, but I am under the impression you will get a more accurate reading if it comes just after the exhaust manifold. Anyway, does anyone see any issues at all with O2 sensor being installed in this position? Thanks for feedback.


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The instructions on my PLX wideband states 24" downstream of the head. I have mine just below the bend of the downpipe with no issues.
I'd say that would work fine. You can grind an angle on your bung so it has the 10°+ nose-down angle to drain condensation. Check your documentation for how to alter the ECM settings for the delay in O2 reading. It will make a big difference in the success of auto-tuning. Yours would be shorter lag than one placed further back - which is a good thing.

Just for reference, Bosch (who designed and makes the sensor elements, even the ones used in clones) says as close to the exhaust ports as possible, without overheating (600°C / 1112°F on the sensor wrench hex). They state 6" or more tends to work for this. Farther back is OK, as the sensor has it's own controlled heater to keep it hot enough to read properly, although they also sell heat sinks if it's too close and getting too hot, especially with turbos.

Geek info including temperatures, installation guidelines, etc, on the Bosch LSU4.9 (most common sensor type today):


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Ok. Great. Thanks so much for the information. I‘ll try to get an angle on the O2 sensor bung when I weld it in. I’ll probably have more questions along the way as I’m installing the efi. Thanks again!