# O2 bung location on 84 mk1 GTI with dual outlet swap



## ds1919 (Oct 13, 2004)

84 mk1 rabbit gti 
stock 8v 1.8l JH motor
stock single exhaust 
CIS-Lamda with Oxygen sensor

I am planning on swapping out the single exhaust setup for a dual outlet. But I need to know the best location for the O2 sensor bung. Anyone done this to the dual outlet downpipe/mani? 

I am apprehensive about tapping into the cast iron mani, I'd rather have a bung welded to the downpipe, but it would be nice if someone has already done this and has a specific location of where to weld it.


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## WaterWheels (Aug 14, 2005)

Never did one on that perticular model but have done it to many cars. There is one problem, the sensor itself. If you plan to use the single wire sensor it has to be as close to the cylinder head as possible. It has no heater and relies on the exhaust gas temperature to reach operating temperature. If installed too far from the heat source, exhaust ports, the sensor temperature can vary with engine load and cause mixture problems. This is why they were installed into the exhaust manifolds. The second type of sensor, heated version, can be installed downstream as far as the CAT if need be (or if the CAT has a fitting). It should be placed so it reads as many cylinders as possible (4 of course is best). If it has to be closer to the engine and can not read all cylinders then at least two will be OK. Position it away from moving parts, like shifter linkage, position it so you can service it without removing things, and position it as straight up as possible to allow water to drain off and not enter it. I've placed them in many different locations based on the model/engine/equipment so you need to decide on a good location yourself. If you have doubts about where you pick then post a picture or ask if there would be a problem.


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## ds1919 (Oct 13, 2004)

I poked around the area back there and there seems to be sufficient space to mount one very close to the top flange on either downpipe, both directly in the back, or to the side. I thought maybe someone had a rule of thumb on this.

Also, I noticed that the single manifold is quite longer than the dual, because of the O2 location and also because of the sniffer pipe location. I will take measurements from the bottom of the mani to the O2 location on the single unit, and compare with the possible locations of the dual.

Question, how easy/practical is it to fit the 3-wire O2 sensor to my CIS-Lambda? I like the idea of being able to read all 4 cylinders as opposed to just two....how would I hook up the heater wires?

thanks WaterWheels


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## WaterWheels (Aug 14, 2005)

It's vary simple and as the thre wire versions are not much more in cost it does have benefits. There is one wire which is the signal wire to the ECU (just like the single wire ones). Then there are two wires for the heating element, they can be connected either way. All you need to do is locate a power source which can supply the power with the key in the run position. With many CIS cars it comes off the fuel pump relay and also powers the Aux Air Valve.


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## ds1919 (Oct 13, 2004)

cool, so its just 12v leads that need to connect to the heater wires...

I did a few universal 3-wire installs so that part isnt new to me, I just thought that the "white" heater wires were somehow connected to the brain. 

I'm gonna go the 3-wire route and locate it lower at the collector.

Thanks!:thumbup:


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