I've got a header pipe for a car with the O2 in the CAT. I've been looking around for a header that will work with a manifold with the O2 in it but haven't found any. I was thinking just now about sending the header back and finding the right one for my manifold. But my O2 sensor will not come out of the manifold due to the manifold blocking any access with multiple wrenches and sockets. (can't figure that one)

Anyways if I switch out the manifold which I assume should work just fine and replaced the O2 sensor in the Cat will my ECU have any difficulty reading the O2? Would it be better to put it in the header near the Cat so it reads more like if it was in the manifold.

Any thoughts are welcomed, thanks.

Here's just a little personal story.

My '89 came from the dealer with an exhaust system that had the O2 sensor in the Cat. whith less then 12 months on the road this car ran rich as hell and spewed Black smoke as I was on a trip. Pulled into the nearest Dealership I could find and they told me the O2 sensor failed and they replaced the Exhaust with a O2 sensor before the Cat as well as changeing the oil and plugs.
Of course the car was still under warranty so maybe they went overboard on the exhaust change but maybe the O2 sensor before the cat is a better system.
With this Exhaust changeover, the ECU stayed the same. and I believe the O2 sensor is the same part.
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'75 Jeep CJ5 345Hp ChevyPwrd, two motorcycles, '85 Pickup: The '89 Volvo is the newest vehicle I own. it wasn't Volvos safety , it was Longevity that sold me http://home.no.net/ebrox/Tony's%20cars.htm

None of the Headers I see for sale make sense. Why wouldn't anyone sell a header that worked correctly with the O2 sensor in the manifold. I pulled off google a posting on turbobricks where someone claimed to have an O2 in the manifold and used the same one I ordered. I stopped by the exhaust shop yesterday to talk with the one person who works/owns it and he was sure that the header was the problem, that it was too long on the vertical. The clearance under the car is not at all safe as it is.

My only guess would be that they sent me the wrong one.

3514976 or 840-101 is the number. I really don't want to change out the manifold and find this header won't work with it either. It should be more simple than this. Oh well.

I ran thru this hassle a while back...
The O2 sensor (3 wire) was placed near the Cat in 1989 cuz Volvo found the turbulence just before the cat allowed for a constant stream of exhaust and heat range to accurately measure the output of the gases. 3 wire O2's have a heater element to increase the response time of the ECU.

Most Cats for Volvo (esp the Aftermarket) have a port for the O2 - to my understanding ALL O2's are the same thread and diameter due to Bosch owning the market on them.

If you need a longer wire it's best to splice in (Solder/ Heat shrink) longer same gauge wire to accomidate the Cat situation.

Tim
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'92 244 NOW w/ M47 (Hydra, turbo bars, bilstein, urethane bushings)

I think if you check fcp or IPD website O2 sensors are different part # between 86 and the 89? They also sell and O2 sensor wrench for the manifold O2 sensor removal

I've tried a couple different wrenches including an o2 socket but the manifold has a piece of metal that keeps the wrench from being able to get more than just the edge of the socket's bolt. I can't figure out why the manifold would be like that in the first place. But now the problem is with the header I bought, it doesn't fit right with the manifold I have. It sits too close to the ground. I don't understand why anyone would sell this header for an 86 when I'm pretty sure all the 86 models had the O2 in the manifold making the down pipe a different size than the later models with the O2 in the header or cat.

I'm thinking the only difference with the O2 numbers are with the length of the wiring or so I hope cause I've got a new bosch for the 86.