3.2 with a fabspeed cat bypass

[ismoto]

Hi, have a 3.2 with a fabspeed cat bypass that has two lambda sensors on it - would like to use another for that car which only has 1 access point before the bigger pipe.. Does that work? Which sensor do I use? What to do with the second? Thanks

[Ton504]

Plug it. If you don't know what the other one is for then you probably don't have a need for a wideband o2 sensor.

[ismoto]

Well currently there are two plugged in but I dont know if I need both if I replace the cat bypass..

[chuckr]

I have 3.2 with Fabspeed Euro-Pre-muff. Only one O2 sensor, two sensors are for newer cars,
one pre muff... one after muff, as best as i can remember.

[Autoban]

Newer cars have two O2 sensors. One before the Cat and one after to measure the effectiveness of the cat (learned this from our 2004 Golf we used to have). The Motronic on our cars only needs one input from the O2 before the Cat to manage the fuel management system. You can plug the second O2.

Juergen

[rusnak]

Plug one. You can use the second bung periodically for a wideband O2 sensor such as an LM-1 or LM-2 for troubleshooting or check up time.

I do this before smog check time, to check on the lambda sensor and make sure that the mixture is accurate.

[Reiver]

If I were to plug one it would be the other way around and measuring at the collector not upstream.

[rusnak]

In my case, the stock bung for the Fabspeed is the upstream one. I also wanted the DME sensor to be at the collector, so I welded one in. That's why there are 2 now. I mentioned to Fabspeed that their bung should be further downstream.

I don't know if they listened, but if there are now 2 bungs, then perhaps it's because old stock was modified. For sure, there is no need for 2 bungs in a 3.2 Carrera bypas pipe. I use the original bung for test purposes, making this a true "test pipe", which must have 2 bungs.

[impactbumper]

i plugged mine.

[scarceller]

You can even remove both, without a CAT the DME really does not need the O2 feedback. If you simply remove the stock O2 sensor the DME drops into open loop mode and runs exactly like the Rest Of World (Euro) cars do. I've found that these motors idle better without the O2 feedback.

[detailed 911]

Originally Posted by scarceller

You can even remove both, without a CAT the DME really does not need the O2 feedback. If you simply remove the stock O2 sensor the DME drops into open loop mode and runs exactly like the Rest Of World (Euro) cars do. I've found that these motors idle better without the O2 feedback.

Sal,

Thanks for the tip. If you unplug the O2 sensor, would the sensor still be working after running the engine for some time (e.g., months or years) should a person wish to later reinstall the cat (with O2 sensor) for emissions testing?

Best, --Peter

[scarceller]

The older style narrow band sensors (like the stock one) can be left unplugged with no early failure. However, NEVER leave a WideBand sensor in the exhaust stream without it connected, these WBO2 sensors must have the heater circuit in operation at all times, they will fail very quickly if left disconnected.

With that said, I always recommend you remove any O2 sensor that's not in use and simply put a plug in it's place. In the stock 84-89 setup it's a real pain to get the stock sensor out and if the threads get seized up you often need to remove parts like heat shields and then apply heat to the sensor to get it out. Often thread repair is needed in the bung. If you use a plug and remove it once a year this becomes less problematic.

If I owned a car with no Cat I'd remove the O2 feedback. I also highly recommend a WBO2 gauge in the cockpit so you can see easily what your mixture is doing. You don't need to rely (nor should you) on the O2 feedback to fix mixture, it's far better to know exactly what it is and adjust/fix it as needed. These cars run better without the O2 feedback, especially idle, the motors don't tend to like 14.7AFR at idle, I've found they idle best around 14.2AFR but at cruise loads they run just fine at 14.7AFR

Originally Posted by detailed 911

Sal,

Thanks for the tip. If you unplug the O2 sensor, would the sensor still be working after running the engine for some time (e.g., months or years) should a person wish to later reinstall the cat (with O2 sensor) for emissions testing?

Best, --Peter

[scarceller]

I'm still wondering why you have 2 sensors? One is the stock sensor, this one has three wires, 2 white and one black. The other may be a WBO2 sensor that may have been used for gathering AFR data via a gauge or directly to a laptop. The WBO2 sensors have a much heavier wire harness that carries 5-6 wires. Look at the pic that rusnak posted in post #6 the sensor on the left is a WB while the one on the right is the stock NB.

[rusnak]

Sal, I think I might be the only one running 2 sensors.

In my case, it's because I check up on the DME sensor with an LM-1 at smog test time. I check on the response time and also for Lambda under load. This is to verify general health of the entire system before going in for the smog test.

My Fabspeed cat bypass came with 1 bung, in a position that was not ideal (not at the collector), so I installed one further back, and plugged the original one. This original bung is what I use now, only for maintenance of the system, and to determine if the DME O2 sensor is still healthy.

[scarceller]

Rus,

I see that in your pic on Post #6, it's a great setup. Being able to monitor AFR with the WB is really nice. I do this with every customer as a health check of the overall DME system. I have a sheet I came up with that has you log AFRs at various conditions, you use it to record your results in an organized fashion. If you want a copy of the DOC PM me.

My Personal car has SSIs with M&K 2in2out and I have a bung on the LHS SSI. I then had M&K put another bung at the RHS inlet of the muffler. I can monitor AFR from both banks this way. But I always run my engine open loop, I never feed any data back to the DME but I'm emissions exempt here. I'm even inspection exempt! Crazy state I live in, I suspect some politician must have been a avid car collector?

Love the car and the mascot!

Originally Posted by rusnak

Sal, I think I might be the only one running 2 sensors.

In my case, it's because I check up on the DME sensor with an LM-1 at smog test time. I check on the response time and also for Lambda under load. This is to verify general health of the entire system before going in for the smog test.

My Fabspeed cat bypass came with 1 bung, in a position that was not ideal (not at the collector), so I installed one further back, and plugged the original one. This original bung is what I use now, only for maintenance of the system, and to determine if the DME O2 sensor is still healthy.

[sagolfer]

Sal,

This is interesting. I've read of many posts from those that install premufflers and struggle with removing the old O2 sensor or get new ones. But you contend that they are not needed with a premuffler?

I was getting ready to install a Premuffler myself and was considering adding another bung hole to add an Air/Fuel mixture gauge. I guess I don't need another hole just eliminate the O2 sensor.

So why have an O2 Sensor even with a working Cat installed? Is the sensor used by the DME to adjust the Air Fuel mixture to maybe protect the Cat?

[scarceller]

With a cat we can't let a rich mixture run unchecked for prolong period of time. The O2 sensor when in closed loop control helps prevent this from happening.

If the Cat is removed simply loose the sensor but do monitor and set base mixture correctly. After that you run just as the Euro cars do.

Originally Posted by sagolfer

Sal,

This is interesting. I've read of many posts from those that install premufflers and struggle with removing the old O2 sensor or get new ones. But you contend that they are not needed with a premuffler?

I was getting ready to install a Premuffler myself and was considering adding another bung hole to add an Air/Fuel mixture gauge. I guess I don't need another hole just eliminate the O2 sensor.

So why have an O2 Sensor even with a working Cat installed? Is the sensor used by the DME to adjust the Air Fuel mixture to maybe protect the Cat?

[Bob Kontak]

Originally Posted by scarceller

If the Cat is removed simply loose the sensor but do monitor and set base mixture correctly. After that you run just as the Euro cars do.

Are you absolutely sure the ROW/Euro 3.2 911's did not have an O2 sensor?

[scarceller]

Originally Posted by Bob Kontak

Are you absolutely sure the ROW/Euro 3.2 911's did not have an O2 sensor?

As far as I know the ROW cars had no cats and had no O2 sensor. The DME for those cars has a different part number and it's missing all the circuit parts for the O2 signal processing but the boards are the same. If you disconnect the O2 on a US car the DME simply falls into open loop within the code. The code is identical for the Euro and US cars, maps are a tinny bit different but not the program code.

I have several cars running open loop without issue.