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What happens if the O2 sensors are connected onto the wrong banks?
likely nothing as long as you have good / similar cats on both sides.
It would be an issue if you were troubleshooting a bad cat / O2 sensor / other issue as the durametric (or other tool) would be providing results for drivers side when it was actually measuring passenger side (and vice-versa).
I'm speaking to post cat response. It would be quite difficult to connect the pre cat O2 sensors to the "wrong" sides due to O2 sensor lead length.
Note the difference between the post cat sensor location between stock / Speedtech.
NOTE: The actual post-cat bung is hidden behind the other cat's pipe, but is close to the location shown by the arrow.
You can image why the original post cat O2 sensor cable would not stretch to the correct cat, but might just reach the wrong cat on the Speedtech system.
Confused?
Probably my fault, my technical writing skills are blunted today.
And maybe no difference at all if using an X pipe system where the two streams mix.
Stock with bungs hidden, the ones that are visible are actually pre-cat bungs. Speedtech
That makes sense Craig. I was told by the tech today that our cars in Australia come with the post cat sensors unplugged. They are installed in their respective bungs, but simply unplugged with nothing to plug into. Saw it with my own eyes.
However, since collecting my car this afternoon after installation of the cup exhaust, it is running rough at idle and part throttle. Completely fine at WOT. The shop installed mini-cats with 90 deg spacers on the PRIMARY (pre-cat) O2 sensors. I am thinking this may be a problem!? Would this lean the engine out?
O2 spacers should not be used upstream. Precat measurements are feedback to adjust fuel trims. O2 spacers are used on the post-cat sensors to avoid cat efficency CELs.
O2 spacers should not be used upstream. Precat measurements are feedback to adjust fuel trims. O2 spacers are used on the post-cat sensors to avoid cat efficency CELs.
After a lot of reading, that is now my understanding too. I questioned the shop about it before taking the car, so not too happy. As a result of the spacers, at idle and part throttle where there is low exhaust gas flow, the ECU is trimming fuel as the sensor is seeing less gas flow than normal, resulting in rough performance. At WOT it’s fine as there is enough gas flow and after coming to a stop after a WOT pull, the ECU has added a bunch of fuel and the idle smooths out for a couple of minutes, until the cycle repeats. Interestingly when they did the install, they found a rat nest in the right corner of the engine bay and right side O2 sensor wiring was chewed through. At no point did the car throw a CEL so it must not have been too much of an issue. No wonder my cold start or idle has been inconsistent since owning the car!
O2 spacers should not be used upstream. Precat measurements are feedback to adjust fuel trims. O2 spacers are used on the post-cat sensors to avoid cat efficency CELs.
Could this potentially lead to engine damage if it went unchecked? Quite peeved about the outcome given I paid a “specialist” good money to fit the parts (not the mini-cats, that was their idea). You really have to be your own advocate.
Hi Spiller
you need to lengthen the sensor wires to get them to the correct Cat
the original exhaust crosses over, left bank, right hand cat on original exhaust
lengthening is easy to do
while the cup uses the left cat for the left cilinder bank
but if connected to the wrong side, the o2 sensor can detect a wrong mixture, and will compensate for that in changing the mixture of the bank
it will not measure a change as the sensor will be connected to the wrong bench when using the original leads on the cup exhaust
so the ECU will compensate even more again without being able to measure the correction
when doing this correctly, i can confirm the car will run absolutely fine with the cup exhaust
don't know the specifics on the autralian cars
but for the european ones, you certainly need to weld 2 exta sensor threads behind the cats
as the O2 values for and after the cats are measured and compared
Hi Spiller
you need to lengthen the sensor wires to get them to the correct Cat
the original exhaust crosses over, left bank, right hand cat on original exhaust
lengthening is easy to do
while the cup uses the left cat for the left cilinder bank
but if connected to the wrong side, the o2 sensor can detect a wrong mixture, and will compensate for that in changing the mixture of the bank
it will not measure a change as the sensor will be connected to the wrong bench when using the original leads on the cup exhaust
so the ECU will compensate even more again without being able to measure the correction
when doing this correctly, i can confirm the car will run absolutely fine with the cup exhaust
don't know the specifics on the autralian cars
but for the european ones, you certainly need to weld 2 exta sensor threads behind the cats
as the O2 values for and after the cats are measured and compared
Hgo
Hi Hgo,
Are you talking about lengthening the wires for the secondary (after cat) sensors? Australian car does not have these at all so no problem I believe. The primary (before cat) sensors have the same wiring left to right (also same part no.) and I believe can be used on either the left or right sides. My shop is trying this as we speak.
Looking to replace my GMG exhaust on my 996 GT3. I'm looking at Cargraphics. Does anyone here know the difference between these 4 exhausts? Anywhere I can see the sound difference? Thanks in advance.
Of course, after I figure that out, it looks like a PITA to buy it and get it here. Click on the button and it sends an email instead of just buying it. Reminds me of our 1990s websites. haha.
I have had these on my car for the past 5+ years, coupled with M&M headers, and a custom x-pipe with HJS cats. IMO the sound is "loud enough" at full throttle where you can still hear the engine a bit. Zero drone. https://www.fvd.net/us-en/2101119960...-mk2-85db.html
They sound similar to these, but a little deeper in tone:
My car came with Cargraphic complete R-Exhaust, although an old one. It has "medium" silencers, part number CARP96GT3RET.
I have never heard my car from the outside, so made a couple short videos with a helper. It does have a resonance around 2500 RPM that I find a little bothersome. Others have told me that on track it sounds great.
I have an email contact at Cargraphic who answered my questions a while back, pm me if you want his contact info, maybe they have some sound files.
05-21-2021, 12:22 PM
