If i remember right, i've been told by a professional tuner that you want the O2mv reading to be 920mv at WOT/Power Enrichment , right?

 

True....but you'll want to verify it with a wide band O2.

 

Haha.. WELLL..... this is where i've been told by a certain professional tuner that you don't really need a wideband. If 920mv is where you want it.. then that is a pretty narrow band of mv's. If you're way outside this, then the O2 won't read it, but the stock narrow band should read 920 fine. If it's not 920 or close to it, then it needs work.


[Modified by GlockLT4, 9:03 PM 1/25/2004]

 

Oh, and is over 920mv lean or rich? I can't remember. It's been a while since I've done any tuning... I'd like to say lean, but I don't remember.

 

Fire him now and run far far away.


You should never ever tune a car to a preselected millivolt reading unless you have first cross referenced it with a wideband O2 on a dyno to make sure they correlate to the proper reading you want. No 2 cars are identical.

 

Technically....

0 to 449 = lean
450 = stoich
451 to 999 = rich

...but that certainly isn't the way that they work on our cars.

 

How do they work? I'm getting an AKM cable and will be poking around in my ECM soon, just curious.

 

On the dyno with 12.9:1 a/f my car registered 930mv, and at 12.5:1 960mv.

 

interesting...... i need to find out what he says to this.... :skep:

 

Well they work in the same sort of way, but in a much narrower range. It is more like anything over 900 is rich and anything under 900 is lean. That is a very very generalized statement so don't quote it as fact in any sort of way. As you can see that is a super narrow band of readings to watch. I've been tuning my own car to try and get it to 900mv, but I've had mine on a dyno and wideband to know that is 13.0:1 on my own vehicle.

Here is what I mean when I say to cross reference your narrow and wide readings. I took my narrowband O2 scanand divided them by 100 and put them onto the same graph as a wideband O2 scan. These are from the same dyno pull.

Click for fullsize.


Whats nice is that I had a really really sucky A/F curve that day, so I can see what my narrowband sensor does accordingly. Helps for tuning. :yesnod:

You'll also see some really freaking things. If the car goes past a certain lean point the narrowband will go to 000mv. Also if you go too rich the narrowband will also go to 000mv because the extra fuel cools it down too much for readings. A bit of a PIA when you see that because you say to yourself "Great.... am i too lean or too rich." Generally watching the O2 before it goes flatline tells you though. If I saw mine going 900, 920, 940, 970, 000, 000, 000 I'd know I am too rich.


[Modified by scorp508, 11:57 PM 1/25/2004]

 

Scorp... is it individual to the engine setup, or is it individual to the O2 sensors? Put another way, can i use my old dyno from my completely stock engine to cross reference the wide and short readings and it would still be correct for even after changing my cam and programming?

 

Its a combination of a lot of things. Engine setup, O2 sensor brand, O2 sensor location.

Mine is currently located in the #7 primary and is a non-heated unit. I plan on putting a heated O2 down into my collector. When that happens I'll throw that sheet out and start from scratch.

Another thing to consider is when mounting an O2 to at least try to get it parallel to the ground if not higher. You want moisture to be able to drip off of it. Water is a natural byproduct of combustion and when you stop your engine it can collect on the sensor and cause premature failure or inaccurate readings over time.

 

Cool thanks! Guess i need to get a dyno of the new setup for baseline. I also need to find out why the person i talked to said that 920 is what you want to go for.

 

I'd be really interested to see some other people do what scorp has done and compare their wideband/shortband readings... anyone else want to go get some dyno charts and compare. I'll see if i can find my old dyno chart and my datamaster logs from them.

 

If you just want to tune "close" yes you can use the O2 readings but you damn well better read the plugs. It can be close enough to be safe but can never be optimal. Carb guys have been changing jets, reading plugs and comparing et's for many many years. But i think a wideband is the way to go but the only way to know if 12.1 or 11.1 or whatever is optimal afr is to test/dyno/track time.

 

What do you mean by "reading the plugs"? Checking them for whiteness (burning too hot)?

 

Yes, you can find a plug chart just about anywhere that will show proper color. You have to be very carefull doing it that way tho, in the modern era that were in i'd probably use a WB since they're pretty cheap now relatively speaking.

 

Yeah, definitely... i was just curious :). Sounds like i need to get it on the dyno so i can match up my WB and NB readings. :yesnod:

 

You can use the narrow band readings as a refeence to know that you are richer than stoich, but in reality you have no idea as to how rich you are. Thats why these things are known as narrow band sensors. Sometime ago I was told by Ed Wright that as long as I was over 850 mV that was acceptable for PE mode. Well it maybe acceptable for NA cars but I would not chance that with a blown car, not unless I could back it up with a wide band system. in a NA car you can get away with 13:1 or even 13.5:1, ideally in PE a NA car makes its best power around 12.5:1. For safest engine durability and engine life I shoot for 12.5:1 or if I want to squeak every little morsel of power out I shoot for 13:1.

IMHO, Reading plugs today is sort of a misnomer. WIth todays unleaded fuels and very high efficiency EFI systems, you will almost always see a BONE WHITE plug. In the old days that was way too lean, today its normal fact of life. Thats how the big three gets 100k mile spark plug life now a days. You pull a plug out of any modern EFI car that is running good, and I can gurantee that almost all of them will have a sparkling clean plug. When I was tuning cars for a living in a dealership thats all I would see at 25k or even 36k miles. Now they get 100k out of them plugs, and even then they are clean when I pull them. Its just that the electrodes are worn out! My personal car which is a blown 396 LT4 and when I replaced the plugs during my cam swap a few months ago, the plugs that came out were bone white as well. I didn't need to replace them but seeing how I had them out during the spring swap I installed new ones.

So reading a plug today is probably useless, unless you got a full blow race car and you are running leaded race fuel.

 

I always wondered how this works. I make a full throttle pass down the 1/4 mile and then another 1/3 mile at part throttle down the return road, through the pits and maybe right back into the lanes. How are the plugs going to show the correct WOT readings when I just spent 2 minutes driving back to the lanes?