Ok... started my car up today after a few small mods, and maintenence.... (oil change, cleaned up and regapped my plugs, and a few other lil things... nothing that should effect fueling at all.
immediately i noticed she felt ALOT more peppy... like real crisp throttle and all... she just wanted to go... got down the street and around the block and i noticed my AFR's were way high.... like 16-18 fluctuations... I know they say "leaner is meaner" and a lean running engine makes more power... but it is also more dangerous for the engine....
So i was real careful from then on... afriad something was wrong... and that this new found power was NOT a good thing...
well hooked up HPT and started logging... oddly... i noticed that the factory narrow band O2 was acting perfectly normal... oscillating back and forth like everything was just dandy.... But the WB was showing AFR's that should have the NB pegged....
so went back to some old logs where i know the car was lean... and sure enough, in other logs, not even an AFR of 15.8 would move the NB... it just sat pegged at like 135.
Well todays log shows the narrow band giving a signal of 182 but the WB is showing 18.41!!!! the NB was swinging from 860 to 230 very smoothly... but the WB was showing similar oscillations at the same time... but from 15.2 to 21!!!
So one of them is Lying.... I am hoping it is just the WB.... I can recalibrate it... and if it is off all it effects is the gauge and my heart rate when i see 17 at cruise. I hope the car is NOT running lean, and that i can keep this extra power... but i just recalibrated the WB less than a month ago... and been working fine till now... so why would it suddenly get so far out of whack?
it is in a bung in my downpipe.... um... hmmm... trying to guess how far downstream of the turbo....
I can go measure for you if this is important.... (i know WB are supposed to be a set distance from turbo for heat reasons)
I bought my downpipe from someone else, i just made a few mods to make it work better... but it already had 2 bungs for O2 sensors... one about half way down, and another right at the downstream end... it is a large question mark shaped downpipe.. comes straight off the turbo, and does a 180 mandrel bend then a 90 into the exhaust... one sensor is 90* into the 180 bend... the other is right at the final 90.
I assume heat is the underlying issue your getting at here? But why would heat suddenly be an issue when it has been working fine up until now? I would imagine something more than sparkplugs would have to change to create enough heat to skew WB readings that much.
But Ron, you my friend are the master, and far be it from me to doubt your advice.
Actually moisture can be the issue, if water gets on the sensor (through condensation), then it can throw readings off or ruin the sensor. It depends on how it's oriented (its supposed to be facing straight down usually, or no more than 45 degrees from straight down).
You haven't run any race gas lately have you?
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no race gas....
and i was wrong... there are 2 bungs in the downpipe.... one right where the dp exits the turbo. and another half way thru the 180 bend... both kinda close to the turbo....
this pic shows them both pretty well. you only see the side of both bungs. The one is right by my ring finger.... the other you can see right between the weld and the turbo flange. mind you this pic would be taken from like the passenger wheel well looking at the engine... so you can see the one closest to the turbo points straight up... but it is so close to the turbo, that is the one i use for the stock NB O2... the other further from the turbo i use for the WB... but i see what you mean about water... that bung has the os sensor facing almost straight up, so anywater in the pipe could run right into the sensor. bad idea.... ouch...
and then here is one that shows the current WB bung better... this view would be as if laying under the car looking up at the sky. but at a slight angle towards the driver side of the sky....
here is a mock up of how it all sits in the car...
looking straight down at it all.
The WB appears to be slowly coming back to an accurate range... before it was reading like 19-20 when the NB was showing normal readings... then earlier it was like 18-19... and then just recently it was as low as like 16-17... so maybe it is drying up and coming back.
so should i swap the 2 sensors? put the WB right next to the turbo where it is safe from water, but exposed to the heat of the turbo?
or leave it there for now and hope this was just a fluke....
I really dont have the time to yank it out and reweld a new bung... I told myself that DP is staying in place till i can get a nice one fabbed up... it is such a tight fit... i dont want to mess with it over a bung.
off topic... but not really... i was just curious... in HPT you set PE target AFR's... if the car doesnt have a WB... which none do... how does the ECU know how to hit that AFR you set.... does it just do some math and take a guess at it? or does it use the NB sensor and some sort of modifier?
always wondered that... VE and everything else made sence... but if is one of the few places that asks for an AFR. so just wondered how the car knows what that afr actually is... cuz it seems to do a pretty decent job of hitting it.
Good question and noticed that myself.
The stock tune actually has it running kind of rich so I made some changes to mine to get it up a tad for more power, especially since I'm n/a with a few mods.
I'd think that with a turbo, you'd want the PE to be somewhere in the high 11's to very low 12's depending on your setup.
I'm also listening in on the thread if you don't mind.
Misnblu.com
Newbie member since 1999
Thank you Dave and JBO! 
I have found that my WB and factory NB are nowhere near close to each other. I never gauge what the WB is doing from the NB.
FU Tuning
So basically you're using the wide band to do all of your tuning while using it to make sure that the car is running correctly, yes?
Thanks John.
Misnblu.com
Newbie member since 1999
Thank you Dave and JBO!
I'd swap them, if it's easy enough to get to. The increased heat will reduce the life of the sensor, but so does condensation...
As far as the PE Target AFR, the car doesn't use the O2 sensor at all when it's in PE mode, which is why having accurate VE tables is so important. It uses the VE and some other numbers that we may not have access to, to calculate the amount of fuel needed to hit the target AFR. This may be way off if your VE table is wrong, or your injector constant is wrong, etc. Think of the AFR target table as a number you are trying to hit IF your car was perfectly tuned, which most time's it's not.
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Excellent information Shifted.
That satisfies my curiousty about it.
Misnblu.com
Newbie member since 1999
Thank you Dave and JBO!
