just installed the scanmaster, i'm gettting 950mv WOT, no retard. I THINK this is rich, not sure. If it is rich, how do i go about leaning it out, will a AFPR work or i have to actually program the pcm?? Thanks

 

Doesnt mean the car is rich, if its dropping below 450mV, then I would worry because your running really lean. The car is designed to add a richer a/f ratio than part throttle at WOT.

 

Dude you're on crack. If you're at WOT and you're getting less than 800mv you're gonna be in for trouble soon, especially if you have a blower. I'd look for 850-900mv at WOT. You'll need to program as the AFPR will get overridden by the PCM.

 

A dyno and wideband O2 is the only accurate way to tune for optimum AFR. Stock style O2s are only accurate at 14.7:1.

 

Just doing some street tuning, my O2's were reading .950 WOT. When I recently did some wideband tuning on the dyno, the AFR @ WOT on the first pull was 10.5:1...quite rich! Take that info for what it is.

 

k guys, i hear wut your sayin. I'll fix this exhaust leak i have first, then recheck the 02's. Thanks for your help

 

Just curious...A few questions please..

When you were running 950Mv where you blowing black smoke out the exhaust?

Did you get the car leaned out after you saw 10.5:1?

If so, how much did you lean it out to and what did the stock 02s read then?

Finally, how much more power did you pick up?

Thanks for any input.
Claude

 

I like to run my WOT 02s at 850-870s.

 

True...but checking your cars O2 sensor values can give you an ESTIMATE of where your car is at. 950mv is rich no matter how you slice it. Repeating what I said before, 850-900 gets you in the ballpark.

 

Guys, you really need to stop trying to tune by O2 sensor voltage.
As n2ocamaro said they are only accurate at stoich. Anything else is a crapshoot.
I've added fuel to cars on the dyno and watched O2 voltage go down. If anyone cares to explain that, feel free. I've have my ideas though.

And 950 isn't necessarily rich. Around 13.0:1 on one guys car was between 940 and 960.

 

Illustrates exactly why you do NOT want to tune with a narrow-band sensor. At richer mixtures than stoichiometric, the sensor mV output is EXTREMELY sensitive to operating temperature. Much more sensitive to operating temperature than it is to A/F ratio. Adding fuel could have cooled the EGT and caused the sensor output to drop, even though it was running richer.

 

That's what I figured.

 

Lets make a sticky on not trying to tune our cars using our 02's.

Another little tidbit to help:

at 14.7:1 AFR our 02 are supposed to be 450mv, but there are variances you know these are not precision items for the few dollars we buy them for.

On top of that, say your car goes to 14.5 AFR, well the 02 is reading like 550mv (don't know, but work with me). This is to keep them accurate in a VERY tight AFR range.

Now you go to 13 AFR. The 02 says 880mv..oh not rich enough eh? go to 12 AFR and they read 900mv. Now you can get a better idea on how they are calibrated.

Someday I am going to find that graph I found on our 02's again and post it for all to see.

I developed a spreadsheet that did show on an average basis where my 02's were reading comparatively along my whole RPM at WOT. However, at the time I had no starting AFR to go by, so my readings meant nothing. All I could tell is that I was leaner in some areas than others, but compared to what?