I'm using EvoScan to monitor the safety of any changes I make via EcuFlash. After doing some baseline runs on my completely stock IX, I'm getting O2 sensor voltages as high as 0.936. My question is whether or not this is useful info. I know I would need a wideband to get truly accurate A/F numbers, but could I still monitor safety with the O2 sensor voltage? Is there a cutoff voltage that I don't want to go over? I'm not looking to push the envelope with my tuning, I just want to do some mild changes and check the safety.

 

More than likely that is very rich since evos come very rich from factory, but o2 will only give you a good guesstimate, wideband will be necessary to be dead on.

 

It is very doubtful that you can extract meaningful data from the narrowband O2 sensor beyond knowing when your AFR are at stoich (14.7 AFR for 100% gasoline). The narrowband sensor will give different voltage readings, but the AFR at which it generates any specific voltage can change, depending on operating conditions.

For more details, check out this article: http://www.innovatemotorsports.com/resources/news3.php

l8r)

 

Then how come some people have tuned there cars using the narrowband?

 

"Ye pays yer money and takes yer chances..."

IMO that's like asking "why do some people try to do 120mph in rush hour traffic?" It can be done, but it's probably not the wisest/safest thing to do and tends to have mixed results.

l8r)

 

Early on it was "Affordable" and a risk some were willing to take.. The Narrowband sensor has a few tenths of a volt and a few milliseconds lag.. Enough to do damage if your doing some hardcore tuning if you make a mistake..

Heck, People did surgery with hacksaws and sewing needles during the civil war.. Doesn't mean It should be done now..

Look at it from this point of view.. If you were standing right next to Osama Bin-Laden, would you have the sniper use his super accurate sniper rifle? Or a shotgun that sprays pellets a few feet outside of the target (where you would be standing)

Sure the shotgun may work, but would you (aka your engine) be willing to take the hit too?

 

^ LOL, I like the analogy.

l8r)

 

I got more..

Would you get your tatoo with a needle or a steak knife?

 

I take the steak knife.

 

I just made a pull using an FJO wideband, and logging at same time.. The wideband was at 10.9, but the voltage said .87, some may see 10.9 and see voltage of .93 so it varies

 

Interesting. So is 10.9 considered pretty rich for open-loop conditions? At what point does the AFR become unsafe?

 

HA! I totally understand what your sayin. WIDEBAND is the way to go. Sorry to steal the thread but... When its time for your wideband to retire does it not work at all or just give false readings?

 

It depends on which wideband sensor you have. According to Klaus at Innovate, the Bosch units they use are accurate over a smaller range of AFR's as they get older; i.e. an older sensor may only be accurate between 90% of its original range. Not sure if the end-of-life is gradual or catastrophic, though.

l8r)

 

That depends on your state of tune and your fuel. However, as a general guideline (and I'm sure people will argue this) on an Evo VIII, I would say:

91 Octane - 11.0 AFR is about as lean as you want to go
93 Octane - 11.2 AFR is about as lean as you want to go

...as always there is some car-to-car variance. I used to run at 11.4:1 on 93 Octane, but I would get pulled timing at times when doing 4th gear pulls. These days I shoot for 11.0:1 on 93 Octane. (although my car as it sits right now is at 10:1 ... it's a long story... )

l8r)

 

and i tunned mine to 11.8 a/f dropping down to 11.4 towards redline on 3rd gear pull with zero knock.

from what i have seen on the forums, most tunners will tune to 11.5 a/f on 93 octane.