Wideband sensor after the cat

[Fullboogie]

How far off will the readings be? I've heard about a half point - does that sound right?

I'm having some exhaust work done on my car right now, and there appears to be no room for a third O2 bung anywhere before the cats, so it looks like my only options is after the cat. I've got an offroad H that I will be running too, but on occasion (inspection) I put the factory setup in there and would like to retain my 02 readings - sometimes it takes a while to get it back on the lift to swap pipes.

So - half point leaner after the factory cats?

 

[JeremyH]

The point of a wideband is to have an accurate a/f reading, don't even bother if its after the cat. You want it as close to the header collector as you can get it. Its hard to believe there isnt any room, I wouldn't go off an offset from someone else's setup.

 

[Rynez06]

How far off will the readings be? I've heard about a half point - does that sound right?

I'm having some exhaust work done on my car right now, and there appears to be no room for a third O2 bung anywhere before the cats, so it looks like my only options is after the cat. I've got an offroad H that I will be running too, but on occasion (inspection) I put the factory setup in there and would like to retain my 02 readings - sometimes it takes a while to get it back on the lift to swap pipes.

So - half point leaner after the factory cats?

to be completely honest... i on my dyno i have put the o2 before and after the cats and had no difference in readings, that being said i use a high quality autronic NTK sensor on the dyno.. the only time i see major differences in af is when the cats are clogged or becoming clogged...

 

[TexasBlownV8]

If you're using cats for inspection, just dont get into it as hard. Or leave the widebands out during that time.

 

[Fullboogie]

I knew it would be a touchy subject. I'm having some exhaust work done right now (removing the factory X section and having an H installed) and though I'd have the guy weld a bung in there while it's on the lift. Figured it couldn't hurt as long as it could be installed in the proper location - if I don't want to use it, I can plug it. But he's having a lot of trouble finding a spot before the cat, on either side, where there is enough room. Might have to scrap the idea...

 

[01yellerCobra]

When I first put the headers on I put the wideband after the cats until I could get to an exhaust shop to weld in a bung. There was about a 1 point difference between before and after moving the sensor.

 

[BruceH]

I have mine after the cat. The wideband used when I dyno is consistantly .3 leaner from the tailpipe vs before the cat. When driving around the af readings are fairly close to what they should be. I monitor a/f and fuel trims all the time with interceptor gauges.

 

[JeremyH]

This is exactly my point, your going to get guys saying there is no difference or .5 or 1 full point difference, everyone will have a different result. So why risk it? Put it where it supposed to go to get the most accurate reading. My 2 cents.

 

[Fullboogie]

Agreed, Jeremy. Probably the best approach.

 

[JeremyH]

If your looking for a good spot to put it throw up a picture of your exhaust setup. And on a side note, your still running cats?... lol

 

[bigray327]

I agree with not doing it if you can't do it right. I'm a little perplexed about there not being room. My one-day-a-year inspection pipe is custom shortened for use with the long tubes, and there's plenty of room.

 

[Fullboogie]

If your looking for a good spot to put it throw up a picture of your exhaust setup. And on a side note, your still running cats?... lol

Inspections in Houston have gotten very California-like. CAI? Fail. Offroad H? Fail. Aftermarket cats? Fail.

I basically have to return my intake and exhaust to stock every year to pass. That's why I want to get my wideband in my factory pipe. Keep in mind, this is a 5.4, so the clearance problems are different than on a GT...

 

[BruceH]

This is exactly my point, your going to get guys saying there is no difference or .5 or 1 full point difference, everyone will have a different result. So why risk it? Put it where it supposed to go to get the most accurate reading. My 2 cents.

I do alot of things that smart people suggest I don't do, lol. There are some variables to think about. Stoichiometric in the tune matching the pump blend, the precision of a $40 Bosch sensor with a $100 controller, if all the cylinders are getting the same charge, you see where I'm going.

I'm not saying it's the best way to do it but it is better than nothing. Mine ended up there when I took it over to a friends house for welding. It's pretty hard to bitch about a favor. I could of taken the h pipe off and had it redone but I tried it out and it provides a good reference for me.

 

[JeremyH]

I do alot of things that smart people suggest I don't do, lol. There are some variables to think about. Stoichiometric in the tune matching the pump blend, the precision of a $40 Bosch sensor with a $100 controller, if all the cylinders are getting the same charge, you see where I'm going.

I'm not saying it's the best way to do it but it is better than nothing. Mine ended up there when I took it over to a friends house for welding. It's pretty hard to bitch about a favor. I could of taken the h pipe off and had it redone but I tried it out and it provides a good reference for me.

I agree with alot of things you do Bruce, but not this one lol, its one of those things that you should do right or not at all imho. Im sure you felt more comfortable doing it on your own car since you verified the offset and tune your own car, but theres just uneeded risk for the average guy wanting an accurate wideband reading as well as a spot where the tuner will read when tuning the car.

Also the time it takes for the wideband to respond is delayed a bit moving it back which I have seen first hand. Obviously we arent reading individual runners here and cant account for bad fuel etc, as always shit happens, but why put yourself in a position to get a less than idea reading? My 2 cents

 

[Fullboogie]

It appears the shop was able to finagle the sensor into the driver's pipe above the cat, but it's going to be a beotch to install/remove the sensor. In any case, this thread has certainly been informative and confirmed my understanding of sensor placement.

 

[Vapour Trails]

My sensor is after the cat and reads similarly to when the car was tuned. My car was tuned by a guy with a M.Sc in Engineering that teaches courses at the local university and holds NHRA records. I asked him about the placement of the sensor and he wasn't concerned at all by it being after the cat by less than a foot and I wasn't in any position to contest his knowledge or experience.

No sensor/gauge combo that is only a couple of hundred bucks is that accurate anyway.

 

[OneQwkStang]

My sensor was welded in before the cat because that was where the install instructions said to put it........+1 for reading instructions, and +1 for following them.lol

 

[Riptide]

Don't a lot of tuners use sniffers clipped on the end of the line to tune with?

 

[Fullboogie]

My sensor was welded in before the cat because that was where the install instructions said to put it........+1 for reading instructions, and +1 for following them.lol

My problem was with logistics. At the time I made the post, the exhaust shop had said there was absolutely no room to install the sensor pre-cat. My question was about accuracy of the readings if installed post-cat for those short intervals when I will run the factory H instead of the offroad H. But as mentioned above, we got it installed so all is good.

 

[ctt326]

Don't a lot of tuners use sniffers clipped on the end of the line to tune with?

Yes, a LOT of them do.