MY03 O2 sensor question

[atmorris]

The shop manual and diagrams I have access to are a little confusing, and I haven't crawled underneath yet. Can someone tell me if an '03 base Boxster has 1 O2 sensor on the precat or 2 ?

I have a set of headers to put on that are set up for an O2 sensor on the collector. I am going to retain the stock mid pipes with the main cats and O2 sensors, but if there are 2 on the precats..... I don't know what to do with the second one !

[Tool Pants]

I forget what year this is but it should be like your 2003.

[mikefocke]

Each side has 2 sensors, one on the pre-cat and one before the main cat.

http://mike.focke.googlepages.com/oxygensensors has pictures of both stock and after market headers side by side

[atmorris]

Yea, I see that both of your posts show 2 O2 sensors in the pre cats. The headers I have contain only one bung for an O2 sensor:

and the diagram shows 2 in the pre-cat and one in the mid pipe.

I was under the impression that there were 4 O2 sensors total, and that if I bought headers that would accept the front sensor, and retained use of the mid pipe with the main cat and O2 sensor, I'd be OK and have no CEL problems. Also, Jeremy from iA told me these headers would not produce CEL. I don't see how that will be the case, if the stock header and pre cat has 2 sensors. Also, the only sensor that looks like it can be installed into the bung on the headers is the one at the rear of the pre cat, the front sensor cable isn't long enough to reach. Wouldn't it be the front one that would need to be installed in the header collector ?

So, what's the solution then, assuming I want to use the headers with the stock main cat pipes ? What would I have to do with the extra sensor ?

Edited March 15, 2007 by Andy_M

[atmorris]

OK, I jacked her up and crawled underneath last night. The stock stuff looks as Toolpants said it should: one O2 sensor at the front of the pre cat, one at the exit of the pre cat, none in the mid pipe with the main cat. The headers have a bung for an O2 sensor, that's great, only problem is the stock header with the pre cats has 2 sensors. So I would assume that this means the frontmost sensor needs to get installed in the header bung, and the output side sensor would have to move to the output side of the main cat. The problem with that is there is no way the front O2 sensor cable is going to reach the O2 sensor socket on the header collector, and there is no way the other sensor cable is reaching all the way back by the muffler to pickup the exit side of the main cat.

I think I recall reading somewhere that you can't lengthen these sensor cables because it changes the timing of the signal and it won't work. Are there other Porsche cables that can be used? Does someone make aftermarket cables, that are extended for this purpose?

So for anyone who has put headers on a MY03 2.7L base Boxster before, and kept the main cats, how did you do this? Even if I bought the sport cats (which I can't), I'd still have the cable problem wouldn't I ? :help:

[mickf]

I think I recall reading somewhere that you can't lengthen these sensor cables because it changes the timing of the signal and it won't work.

I lengthened my cables and had no "timing" problems. The problem I did have was getting good, durable splices. I'd seen conflicting info on whether solder or crimping was best, so soldered two extensions and crimped the other two. I searched for but never found any pluggable extensions.

If you use copper extensions, as I did, then crimping is the way to go. The problem with soldering is that the OEM wiring is stainless steel, which doesn't solder well to copper -- at least not with the Radio Shack solder I was using. I've done a lot of soldering over the years and never had this problem before, but had never tried to solder these two metals together either. Several of the soldered joints failed resulting in CELs. So I redid all the soldered joints with crimps last October, and nary a CEL since then.

Good luck,

Mick

[atmorris]

I think I recall reading somewhere that you can't lengthen these sensor cables because it changes the timing of the signal and it won't work.

I lengthened my cables and had no "timing" problems. The problem I did have was getting good, durable splices. I'd seen conflicting info on whether solder or crimping was best, so soldered two extensions and crimped the other two. I searched for but never found any pluggable extensions.

If you use copper extensions, as I did, then crimping is the way to go. The problem with soldering is that the OEM wiring is stainless steel, which doesn't solder well to copper -- at least not with the Radio Shack solder I was using. I've done a lot of soldering over the years and never had this problem before, but had never tried to solder these two metals together either. Several of the soldered joints failed resulting in CELs. So I redid all the soldered joints with crimps last October, and nary a CEL since then.

Good luck,

Mick

Yea, I checked with our EE this morning and he said that timing of the signal wouldn't be a concern. He was a little puzzled as to why soldering would not be the preferred method because generally there would be less loss, but I didn't know at the time that the stock witing was stainless.

Did your main cats have O2 bungs in them already? Or did you have to add one to the outlet pipe from the main cats? I didn't see any in mine, although I didn't look at them thouroughly yet. Maybe there are knockouts or bungs I didn't see.

Toolpants?...MY03 main cats ...do they have some provision for O2 sensors that I can take advantage of? If not are their specific dimensions that the sensor mounting bungs would have to be made to? (height, thread, etc..)

[mickf]

Did your main cats have O2 bungs in them already? Or did you have to add one to the outlet pipe from the main cats? I didn't see any in mine, although I didn't look at them thouroughly yet. Maybe there are knockouts or bungs I didn't see.

The main cat has a bung near its outlet. It's on top so may be hard to see just looking underneath the car. Take a look at the very top of the diagram in your earlier posting & you can see where the sensor screws in to the bung.

[atmorris]

Did your main cats have O2 bungs in them already? Or did you have to add one to the outlet pipe from the main cats? I didn't see any in mine, although I didn't look at them thouroughly yet. Maybe there are knockouts or bungs I didn't see.

The main cat has a bung near its outlet. It's on top so may be hard to see just looking underneath the car. Take a look at the very top of the diagram in your earlier posting & you can see where the sensor screws in to the bung.

I see it. Now I just hope that there isn't already another O2 sensor that I didn't see stuck in that bung that I didn't see........if not, I'm all set ! :clapping:

[atmorris]

Did your main cats have O2 bungs in them already? Or did you have to add one to the outlet pipe from the main cats? I didn't see any in mine, although I didn't look at them thouroughly yet. Maybe there are knockouts or bungs I didn't see.

The main cat has a bung near its outlet. It's on top so may be hard to see just looking underneath the car. Take a look at the very top of the diagram in your earlier posting & you can see where the sensor screws in to the bung.

I see it. Now I just hope that there isn't already another O2 sensor that I didn't see stuck in that bung that I didn't see........if not, I'm all set ! :clapping:

Well, that would have been too easy. The MY03 main cat apparently has no such bung for an O2 sensor. I felt all around the outlet side - nothing there. I guess I will have to take the midpipe all the way out and have someone open a hole and weld a bung to it for the sensor. Anyone know where I might be able to buy a couple of weld on bungs for O2 sensors ? I think I remember seeing something on the Pellican website once......

What are they 18mm ?

[mickf]

Well, that would have been too easy. The MY03 main cat apparently has no such bung for an O2 sensor. I felt all around the outlet side - nothing there. I guess I will have to take the midpipe all the way out and have someone open a hole and weld a bung to it for the sensor. Anyone know where I might be able to buy a couple of weld on bungs for O2 sensors ? I think I remember seeing something on the Pellican website once......

What are they 18mm ?

You should be able to get bungs welded on at any muffler shop. If you take a sensor with you along with the exhaust piece getting the bungs, there would be no question re fit. Unless you take the car to have the work done, you will need to mark exactly where you want the bungs placed and give full consideration to the space needed to accomodate insertion of the sensor and routing of its wires.

You should have the new bungs placed somewhere after the remaining cat. The placement on your stock 03 before & after the pre-cat, and on earlier models before & after the main cat, tells me there should be a catalytic converter between the two sensors on each side.

[atmorris]

Anyone know if it matters where the O2 sensor is put in the main cat, other than on the outflow side? The stock location appears to be in the angled endface of the cat rather than in the outlet pipe itself. My inclination would be to follow that example.

[atmorris]

Anyone know if it matters where the O2 sensor is put in the main cat, other than on the outflow side? The stock location appears to be in the angled endface of the cat rather than in the outlet pipe itself. My inclination would be to follow that example.

Update: Got the O2 sensor bungs from Summit Racing and we installed them this weekend. Did not install the bungs in the "stock" rear cat location (cat endface). We started drilling a pilot hole in this location on the cat and ran into another surface about 1/8" under the outer shell. Not being certain what that might have been, we stopped right there and welded that hole closed. We put the bungs in the pipe immediately after the cat instead.

I extended all 4 O2 sensor harnesses to 36" as the fronts needed some extra length to be kept safely away from the header tubes.

Also noticed that an oil line is running WAY to close to the header tubes and zip tied that back away from the headers. Have a heat wrap coming for that line today from Advanced Auto Parts as well. I might even add a shield to that area to be sure that line doesn't contact the headers. Anyone else solve this problem another way ?

Andy