best place for a wideband on a v6?

[NicoNO82]

sorry prolly been asked before.

so I need to get a wideband and install, figure ill let a shop do the welding since i cant.

problem is in thinking about it, i need to place the sensor ahead of the cats right?

but i have three f'n cats on my truck?!

so i was wondering and figured it should go as far upstream as possible. BUTTT i have two cats upstream each on seperate bays. is it accurate to throw the wideband infront of one of them or should i get two widebands. The collector is after the two upstream cats so its not eally a good place for it.

ideas,
place in collector and drill out cats?
buy two as pricey as they are
eliminate rear o2 and use bung but still prob with forward cats.

would my reading off of one bank be accurate enough to tune or do i really need readings from both banks?

 

[Wicked_Sludge]

id put it in the y-pipe where the two banks meet. this way youll be reading both banks. the upstream cats shouldnt effect your a/f readings much (the factory O2's are behind them after all).

 

[NicoNO82]

i was looking at it today. actually there are two o2's right up in the downpipes containing the front cats, before the cats right after the flange to conect to the exhaust manifold. then there is one efficiency o2 mounted behind one of the front cats and thats it. I might put the wideband behind the other cat. or maybe in the collector. however the actual collector is another cat. two pipes are seperate when they hit the flange but the cat behind combines them.

 

[Wicked_Sludge]

the primary O2's are that high on the system huh? i seem to remember them being after the first cats, but ill admit its been a while since ive been under a newer truck.

in that case, you might want to consider installing the sensor right next to one of the stock upstream ones. i dont see the cats messing with the mixture THAT much, but they could potentially remove air from the system, hiding a dangerous lean mixture condition.

 

[rurouni20xx]

i find it rediculous that they now install cats in the headers on some models, and unless you have a sensor per cylinder in the damn headers you really can tell anything unless you cut the cats out (which your not supposed to and i do not recommend it at all) the header cats in newer models actually reduce initial emissions and create slight backpressure right against the valves to keep the fuel in the cylinder, and also making the computer lean out heavily, which is horrible for the motor. the newer model motorcycles do this as well thats how im familiar w/ it, when we take a reading we do it on the headers themselves 6 inches below the exhaust ports and have to shut the air induction system off to get a proper reading. yes i said ais. they induce fresh air from the airbox into the exhaust so itll burn better by the time it gets to the cat by raising the temperature. only way to get a true reading at all is to shut it off. idk if cars utilize this yet but it wouldnt surprise me one bit as motorcycles have been doing this as of 2002. i know this may sound crazy but my recommendation is drill and tap the headers in front of the cat on either side and place the sensor there that way you get a true reading of whats going on b4 the cats. at least thats what i would do, im thanking god i have an older vehicle that only had two cats behind the y pipe and now have a single 3" high flow cat that i can get an accurate reading b4 it gets that far.

 

[Wicked_Sludge]

stock motors do not come with headers, they come with manifolds. the 3 cylinders on one bank are merged into one before they connect to the downpipe. one sensor on the downpipe before the cat will read all 3 cylinders from that bank, there is no need for 3 seperate sensors.

the engine does not lean out due to the cats. the PCM leans it out to speed the engine up to operating temperature to reduce emissions and provide better fuel economy and drivability.

smog pumps and air injection havnt been used in automotive applications since the early '90's.

 

[rurouni20xx]

i see and pardon my misuse of terminology, i call exhaust manifolds headers all the time cuz thats what they are on bikes, sorry for the confusion. the last sentence on my post was place the o2 sensor on then end of the manifold b4 the y pipe connector. ive known about the good ole smog pump, didnt know about the injection. in bikes the added backpressure pushes the gases back into the heads, so they ll reburn and the computer leans out as to not overcharge the cylinder making it really rich, it is apparent that m/c systems and autos are way dif technology, and ill keep my mental observations and correlations to myself in the future.