Installing An O2 Sensor in the Headers

douglas robbins · 08-04-2003, 01:40 PM

I'm interested in installing an O2 sensor to help the Motronic brain manage proper fuel delivery but the problem is, where would I install the sensor?

I have a 1984 3.2 Carerra engine in my 914-6. The engine pipes through headers and the headers meet the muffler in two different places (about a few feet apart). There is no cat.
So this is the problem: in a stock 3.2 the O2 sensor was mounted in the cat.

My problem is that at no point before my gasses reach the muffler do the pipes all come together like they do in the stock 3.2 motor where the cat usually is. So I don't know where to put the O2 sensor to get an equivalent reading. Anybody ever deal with this?

Douglas

Bill Verburg · Bill Verburg's Garage

When headers and a single O₂ sensor are used it is usually setup like this

The factory placed the 993 where the 2 sides come to gether but that is not necessary.

douglas robbins · 08-04-2003, 02:28 PM

Bill,

You rule. So to clarify, the O2 sensor is only reading gasses on one of the two headers (reading only gasses on three cylinders). Which header/cylinders should the reading come from, or does it matter? And does the sensor have to be positioned vertically on the top (12 o'clock), or can it be installed horizontally on the side (9 or 3 o'clock)?

Douglas

Bill Verburg · Bill Verburg's Garage

I've always installed mine in the top half of the pipe, where there was room, I think that it may be drier there, or at least the water will drain away more quickly. On my B&B header the bung was located by B&B, it appears that they agree w/ me.

Here is a US 993 OBD2

As you can see they installed them horizontally. They use 4 on these cars.

Wil Ferch · 08-06-2003, 06:09 PM

Douglas:
When I went with a Euro pre-muffler to replace the cat on my stock 85 3.2 Carrera... I noticed that the premuffler had two major pipes coming together just ahead of the main body of the premuffler. I located the O2 sensor almost identically to where it was for the cat, but in this location it was inserted into the upper pipe that got gasses from the opposing bank of three cylinders.
No problem.....

---Wil Ferch