Hi Ben. Can you provide any links etc to support that claim? I have always believed that WBO2 works fine after CAT.

 

Read the links I posted earlier. They will recommend not placing them after a cat.

 

From my OE experience, we don't put the WB02 before the cat.

 

Can you point to a specific application? The only post cat O2 sensors I'm aware off are the narrowband sensors used to check CAT efficiency.

 

There are a lot of dyno shops out there using a WB mounted in a small pipe section which gets inserted in the tailpipe.

 

That is correct, and they are tuning WOT only, the cats have little effect here. But when you are doing drive around tuning you are concerned with more than just WOT, you need info from tip in, cruise, part throttle accel and even sometimes decel. The cats effect these ranges.

 

Knowing how a WB works, my gut says it should work post-cat. A cat only makes the exhaust look like it has gone through a more efficient engine.

Of course a WB will not read correctly after any air-injection system.

 

A catalytic converter splits nitrogen oxide molecules into nitrogen gas and oxygen gas. It also combines carbon monoxide and oxygen gas to create carbon dioxide.

Since your oxygen sensor is measuring the amount of oxygen gas in the exhaust the catalytic converter is obviously going to effect the reading.

 

A lambda sensor measures AFR not oxygen content.

 

Source for your argument?

Here's mine.
https://en.m.wikipedia.org/wiki/Oxygen_sensor

"An oxygen sensor (or lambda sensor, where lambda refers to air–fuel equivalence ratio, usually denoted by λ) is an electronic device that measures the proportion of oxygen (O2) in the gas or liquid being analysed."

 

Yeah, been here before. The sensor measures the oxygen concentration on the platinum electrode not the concentration in the exhaust gas. The environment on the electrode is similar to the platinum catylist in a catalytic converter.

Talking about the narrow band sensors now - only because they are much simpler. What happens is Oxygen ions migrate from the atmospheric electrode of the sensor towards the exhaust electrode - because the Oxygen concentration is always lower on the exhaust electrode. The greater the difference in concentration, the greater the voltage. However - even when the exhaust Oxygen concentration gets to zero, the voltage can still get higher as the mixture gets richer - because the unburned fuel products arriving at the exhaust electrode (platinum remember) are reacting with the Oxygen ions arriving through the sensor electrolyte and removing them creating what is effectively an even lower concentration of Oxygen ions.

"Operating characteristics of zirconia galvanic cells (lambda sensors) in automotive closed-loop emission control systems
Bozek, John W | Evans, Richard | Tyree, Clifford D | Zerafa, Kenneth L
SAE Special Publications , no. 910, pp. 1-17. 1992

Extract.

 

Here is an excerpt from Dynojets install instructions:

"On vehicles equipped with catalytic converters, Dynojet recommends installing the weld boss before the converters. Vehicles that do not utilize catalytic converters are free to install the boss anywhere in the exhaust, but we recommend keeping it within thirty inches of the exhaust port. Turbocharged vehicles have rather high exhaust gas temperatures and pressures. In these applications, it is best to install the weld boss in the down pipe as far away from the turbine as possible"

Here is one from Summits instructions: (Same as AEM instructions)

On turbocharged engines the sensor must be installed after the turbo charger, if not, the pressure differential will greatly effect the accuracy of the unit. For accurate readings, the sensor must be mounted before catalytic converters and/or auxiliary air pumps.

Glowshift says:

locate an open space on the exhaust before the catalytic converter

Literally every manufacturer I can find says specifically not to mount post cat, and not to mount pre turbo.

My personal recommendation is not to mount the wideband clear at the end of the vehicle, that causes a lot of transport delay. It isn't a huge deal at WOT and tuning top end, but it can be a real pain when you are trying to tune the drive around characteristics.

The solution is to move the turbo to the engine bay

 

"Move it under the engine bay" lol, your not wrong but it was a lot cheaper to do it rear mount. It was fun until tuning became an issue as well. The fact that tuning became an issue down the road is what has got me stumped. Plugs look great, o2 WB placement we have now established is wrong, still haven't got a real clear answer on NB o2 but I need to read through these replies a bit more thoroughly. I have also found that some sort of insect has made a nest in my wastegate, which surely caused some issues on my last couple test drives, I don't have much time when home to work on this so its and hour or so, change tuning map, find more mechanical issues from sitting, take 1 or 2 five minute test drives. Its a shit show right now to say the least. For the time being I am going to fix know issues, if no improvement I will install meth injection and hope I can get my piggyback to play nicely with it. If they wont get along I'll go back to stock injectors and ecu with meth and if that will not work... then hell with it, going to run it till it pops and just go with with a lexus v8 swap with a SC.

 

Touching on the decel subject, what information can I gather from this? I do notice on decel, it'll do the typical cut to min fuel and shows 22 something on afr, you blimp the throttle and it'll jump right back to "normal" operating range. But occasionally it'll go just pig rich on immediate throttle lift, 9.2 range.

 

Trying to wrap my head around this, is this all referring to running the narrow band post or pre cat? What are your thoughts on running is post or pre Turbo? I'm wondering if the "simplicity" of it makes it acceptable for pre turbo but now reading the vast difference on voltage on a small amount of change, could the turbo have a great impact of the reading than I realize?

 

This is normal. What you are seeing is DFCO engage (deceleration fuel cutoff) it aids in engine braking and saves fuel. The immediate throttle lift richness is normal as well, there is residual fuel stuck to the manifold walls that ends up dropping into the cylinders and the ecm is still spraying what it thinks it needs to to keep the engine happy in the conditions. It won't hurt anything, its a high vacuum low load situation, and a tiny amount of fuel (tiny amount of air makes a rich condition).

It would be a good experiment to measure your exhaust pressure. Install port, install a length of copper to let the gas cool and attach to a cheap boost gauge. We may be splitting hairs, I have no idea what drive pressure on a remote system is. There must be a sensitivity threshold on the 02 sensors.

 

For both WB and NB - readings will be similar pre or post cat provided there is no mis-firing, no air injection system and the sensor is hot. Pre-turbo is not recommended due to high pressure and possibly high temperature.

 

Thanks, well I worked out a few bugs and it's running safely with the time I have available between hitches. Still have yet to move the o2 sensor, got the parts and what do you know I was out of gas for the welder and my Norco is closed on Sundays. So hopefully next time I'm home I'll be getting the sensor moved post turbo.

It does sound interesting to find that boost pressure but with another baby on the way it's time for overtime at work . I did more digging at reached out to some folks at URD, who essentially used to be TRD (Toyota racing development) and turns out the stock fuel pressure regulator will increase its own pressure when boost is added, to a reasonable level and the 8 psi I'm running isn't a big deal. So after more research I've found that the piggyback system I have is a pile of hot trash.. Very few have had long term positive results with it. As of now the plan is to move o2 sensor, Get rid of piggy back system and try to run on the larger injectors installed, which are not much over the stock injectors. The guy I based my build from ran the same oversized injectors and had great results. If that doesn't work, it's back to stock injectors, in theory the stock configuration can handle 7psi as most do with the SC. But I do understand the turbo is a different animal so I've got a water/meth kit in my cart to order next month, it'll certainly help with the buildup on the valves anyhow, it's going to be installed even if it only sprays at peak boost, just for cleaning valves. I did read on water/meth you only want to spray at 1/3 boost or greater though, or above 3k rpm as a good starting point for most motors. If I ran injection at 1 psi under 3k rpm I'm not sure how it would effect the engine. Still learning a ton as I go. Thanks for all the information guys.

 

If you can find someone local to you who does HPtuners they may be able to write you out a tune to handle the injectors if you have problems. There is an automatic fee of $100 to write a new vin, but I would think you could find a hobby tuner who would do an injector size for you for a case of beer and the cost to them. If the ECM otherwise already has the logic in place you should be good to go.

 

Unfortunately living in Idaho with the boom of everyone living here. No one I'm the treasure valley will tune it because I no long have a CAT or the fact that no one is familiar with split second software. I'm curious if it's just the ability to take larger profit jobs than a 500-800$ tuning session.