Installing O2 Sensor; Do I need a new exhaust?

[spoke]

Car is '86 930.

I'm adding an AEG AFR and it says the O2 sensor should go after the turbo and before the cat.

Here's a picture of the exhaust on my car. The cat is connected directly to the turbo so it looks like there's no room for the cat.

Does this pretty much mean I need to change the exhaust to one without a cat? I have a line on a Billy Boat exhaust w/o a cat. Not sure eliminating the cat will cause issues with emissions inspection.

TIA.

[993Speedster]

According to most of the wideband manufacturers, they'll tell you in an "ideal" setup it would be at least 6-8" from the turbo discharge but I've got both of mine (1 for ECU, 1 for visual redundancy and fault tracing in future) mounted barely inches from the turbine wheel and have noted no ill-effects. Once the exhaust expands post-turbo side, it's generally way cooler. This distance-based recommendation is made with the fact that most turbo manifolds are really short and close to the exhaust port. 911 style single turbo setups have literal FEET of exhaust path before even entering the turbo.

If you ask me, the most important thing to o2 longevity is mounting and warm-up sequence...

1.) Make sure the o2 sensor bung is pointed UP with a tolerance of 15* in any direction. This keeps moisture from accumulating in the sensor head.

2.) Make a switch for your meter so it doesn't start warming up on key-on before you even start vehicle. If it's hot already and you start vehicle, it sends a big bunch of vapor and exhaust moisture at it and the thermal shock is mostly what does em in... Some widebands have a delay feature as do some standalones with built-in controllers.

[993Speedster]

Not much option other than here.

[flightlead404]

Originally Posted by 993Speedster

According to most of the wideband manufacturers, they'll tell you in an "ideal" setup it would be at least 6-8" from the turbo discharge but I've got both of mine (1 for ECU, 1 for visual redundancy and fault tracing in future) mounted barely inches from the turbine wheel and have noted no ill-effects. Once the exhaust expands post-turbo side, it's generally way cooler. This distance-based recommendation is made with the fact that most turbo manifolds are really short and close to the exhaust port. 911 style single turbo setups have literal FEET of exhaust path before even entering the turbo.

If you ask me, the most important thing to o2 longevity is mounting and warm-up sequence...

1.) Make sure the o2 sensor bung is pointed UP with a tolerance of 15* in any direction. This keeps moisture from accumulating in the sensor head.

2.) Make a switch for your meter so it doesn't start warming up on key-on before you even start vehicle. If it's hot already and you start vehicle, it sends a big bunch of vapor and exhaust moisture at it and the thermal shock is mostly what does em in... Some widebands have a delay feature as do some standalones with built-in controllers.

In addition to that, I wired a relay for my WBO2 controller which is controlled by the microsquirt fuel pump relay pin. It gets power only when the engine is cranking.

[flightlead404]

Originally Posted by spoke

Car is '86 930.

I'm adding an AEG AFR and it says the O2 sensor should go after the turbo and before the cat.

Here's a picture of the exhaust on my car. The cat is connected directly to the turbo so it looks like there's no room for the cat.

Does this pretty much mean I need to change the exhaust to one without a cat? I have a line on a Billy Boat exhaust w/o a cat. Not sure eliminating the cat will cause issues with emissions inspection.

TIA.

We went through all this in excruciating detail via email. However you'll need to check if your state cares about a visual or sniffer test on an '86.

Mine passed visual in Ohio in the 90's because they just didn't know what they were looking at, and the sniffer test because it was tuned well. In GA with a 33 year old car there's no test or inspection at all.

[spoke]

Originally Posted by 993Speedster

According to most of the wideband manufacturers, they'll tell you in an "ideal" setup it would be at least 6-8" from the turbo discharge...

The only guideline mentioned was 30 inches from the exhaust port. As well as downstream from the turbo and before the cat. I'll have to look to see if I can fit the O2 sensor where you mention.

Has anyone else placed an O2 sensor before the cat like you mention? BTW, I like that placement as I don't have to buy another exhaust system.

[spoke]

Originally Posted by flightlead404

We went through all this in excruciating detail via email. However you'll need to check if your state cares about a visual or sniffer test on an '86.

Mine passed visual in Ohio in the 90's because they just didn't know what they were looking at, and the sniffer test because it was tuned well. In GA with a 33 year old car there's no test or inspection at all.

Yes, I appreciate your input. I tend to really evaluate solutions before jumping off. I don't think the PA inspection of such an old car is that detailed. I think all they check is the gas cap.

[flightlead404]

Originally Posted by spoke

Yes, I appreciate your input. I tend to really evaluate solutions before jumping off. I don't think the PA inspection of such an old car is that detailed. I think all they check is the gas cap.

Simple to check with the state, probably on a web site somewhere and a big improvement to replace the exhaust.

[RarlyL8]

If you don't need a cat our muffler will add 12whp while lowering boost threshold 500rpm, allowing quicker throttle response and knocking off 10 pounds where you least need it. Turbos need to breath!

[bpu699]

Do yourself a favor, return the afr you bought. Some of them use on o2 sensor for the afr and the same sensor for the bosch system. No holes, no welding, works great.

[spoke]

Originally Posted by bpu699

Do yourself a favor, return the afr you bought. Some of them use on o2 sensor for the afr and the same sensor for the bosch system. No holes, no welding, works great.

Tell me more. This is what I hoped to have done on my car. Pull the original O2 (or keep it) and put in the new sensor in the same bung; wire it and go. It's been a year now since I purchased the AFR and still haven't installed it.

[993Speedster]

Originally Posted by bpu699

Do yourself a favor, return the afr you bought. Some of them use on o2 sensor for the afr and the same sensor for the bosch system. No holes, no welding, works great.

Originally Posted by spoke

Tell me more. This is what I hoped to have done on my car. Pull the original O2 (or keep it) and put in the new sensor in the same bung; wire it and go. It's been a year now since I purchased the AFR and still haven't installed it.

Sounds like he's referring to purchasing a wideband controller/sensor kit that can output a narrowband signal; some do some don't. Most of the newer more premium ones do.

Essentially you'd have a wideband o2 sensor replacing your narrowband sensor location. It would then output wideband signal/accuracy to the gauge and then still recreates the narrowband switching type output to be fed to your ECU and keep it happy for closed-loop operation.

[spoke]

Originally Posted by 993Speedster

Sounds like he's referring to purchasing a wideband controller/sensor kit that can output a narrowband signal; some do some don't. Most of the newer more premium ones do.

Essentially you'd have a wideband o2 sensor replacing your narrowband sensor location. It would then output wideband signal/accuracy to the gauge and then still recreates the narrowband switching type output to be fed to your ECU and keep it happy for closed-loop operation.

Here's the weird thing with my engine: the O2 sensor has never been connected. Whoever owned the car before me disconnected it. The engine runs great but not sure if they disconnected then adjusted the AFR to compensate.

I picked the car up in Denver and the PO said it was set up to run in the high altitude. Don't know what was adjusted or disconnected.

[flightlead404]

Originally Posted by bpu699

Do yourself a favor, return the afr you bought. Some of them use on o2 sensor for the afr and the same sensor for the bosch system. No holes, no welding, works great.

nah, disagree.

Yes, some controllers can be configured to output a "synthetic narrowband" signal and that's fine but it doesn't address the primary issue.

The backpressure prior to the turbine inlet causes a wideband O2 sensor to read incorrectly.

This issue doesn't affect narrowband sensors (to my knowledge) they work differently. If it does, manufacturers took that into account.

If you want/need to keep your old CIS brain adjusting the mixture in closed loop mode while idling (and this is all it does, once off idle it does exactly zip) then fine, leave BOTH sensors in place. Maybe its easier to do that, but if not who cares? Just adjust your idle mixture to a reasonable place (13.8-14.2 seems good for mine) and call it a day.

But don't put a WBO2 before the turbo and expect to get accurate results from it. And isn't that the reason you want to put a WBO2 sensor in in the first place?

[993Speedster]

Totally forgot that the 930 o2 sensor was pre-turbo. That definitely changes things. Wideband needs to be post-turbo or you need to have pressure compensation which is something you don't want to bother with unless you're doing individual o2's in each cylinder for full-on racecar bankruptcy

[RarlyL8]

I've run O2 sensors in both the J-pipe and in our muffler simultaneously for comparison purpose. What I saw was the AFR readings were a couple tenths to half a point different. When the same setup was performed with a catalytic converter in place the numbers were more closely aligned, leading me to believe this is a back pressure equalization issue. When installing the O2 sensor 6" from the tailpipe there was greater variation with idle and throttle cuts being off the chart lean. I assumed that was due to ambient air back wash. We settled on leaving our O2 bung directly after the turbo in the neck of the muffler. For race applications a heat sink should be used. I've had mine in for over 10 years now in that location with no issues.

Here's the weird thing with my engine: the O2 sensor has never been connected. Whoever owned the car before me disconnected it. The engine runs great but not sure if they disconnected then adjusted the AFR to compensate.

Yes you can remove the O2 sensor and unplug the Lambda "computer" then adjust the mixture to correct. High altitude adjustment for the 930 is typically no more than enriching the mixture to compensate for thin air.

[bpu699]

Originally Posted by spoke

Tell me more. This is what I hoped to have done on my car. Pull the original O2 (or keep it) and put in the new sensor in the same bung; wire it and go. It's been a year now since I purchased the AFR and still haven't installed it.

Google PLX airflow AFR... will defer to others where to put the bung, but it works well...

[Rich76_911s]

In Pa you can get antique tags and inspection is minimal, might even be ignored. Can’t exactly remember.

I have a Fabspeed muffler I’d sell you pretty cheap and your close enough we wouldn’t even have to ship it. If you want to lose the cats. It would need an O2 bung welded on but that should be a $20 job for someone.

Rich

[greglepore]

Originally Posted by Rich76_911s

In Pa you can get antique tags and inspection is minimal, might even be ignored. Can’t exactly remember.

I have a Fabspeed muffler I’d sell you pretty cheap and your close enough we wouldn’t even have to ship it. If you want to lose the cats. It would need an O2 bung welded on but that should be a $20 job for someone.

Rich

No inspection for antique in Pa...fwiw I had normal tags and no cats for 10 years. Car ran clean enough and standards really lax for 80's cars. Visual? People thought the heat exchangers were cats or didn't care.