A/F check by monitoring rear O2 sensors

[Craig99SVT]

I was told by a dyno owner that if you couldn't get to a dyno to check your A/F, in a pinch you could tap into your rear O2 sensors and check the voltage. He said if you were in the 870-880 range you should be OK which should be somewhere around 12.5. Does this make any sense to you guys? Has anybody tried this? And does that voltage sound about right? If so, which wire? I forgot to ask that,lol.

I need to check my A/F and can't get by to my local dyno.

 

[Zinc03Cobra]

TTT for ya.. curious on this one too.

 

[03RedCobra]

That makes sense to me. I'm assuming that the sensor takes a reading on the A/F ratio, turns it into a voltage reading, the computer gets this reading, and then adjusts the fuel as needed. All we would have to do is to tap into this voltage reading with a guage that turn this reading into sensible number that we already understand, like 12.5 or 11.8 versus 870-880.

870 could mean 11.8, 880 could mean 12.5, etc.....

 

[03RedCobra]

additional post.......the only problem is that we would have to have some type of a book that gives us the exact voltage reading and its corresponding A/F ratio reading. Otherwise, I wouldn't go on some guy telling me that a reading of 880 means 11.8 A/F ratio. I'm sure FORD has something that would have these correlating number conversions. Of course, if we can get our hands on it, that would be another thing.

 

[caveman6666]

Too bad the odometer display doesn't pull this.

 

[Shadowgray03]

The o2 sensors in our cars are designed to minitor stoich AF of 14.x:1 and the farther they get from this the less accurate they are. The O2's also operate between 0 and 1 volt if I remember correctly with .5v being stoich 14.x:1. Personally I dont buy it.

 

[jcayer]

I thought they had AF monitors that you can buy that do just that.. they tap into the existing o2 sensor??

Subscribing and TTT for ya!:read:

 

[Craig99SVT]

Originally posted by 03RedCobra
That makes sense to me. I'm assuming that the sensor takes a reading on the A/F ratio, turns it into a voltage reading, the computer gets this reading, and then adjusts the fuel as needed. All we would have to do is to tap into this voltage reading with a guage that turn this reading into sensible number that we already understand, like 12.5 or 11.8 versus 870-880.

870 could mean 11.8, 880 could mean 12.5, etc.....

You're on the right path but the lower the #, the higher the A/F ratio. 880 being 12.5 maybe, then 850 being 13.5-14. At least that's what he told me.

 

[Shadowgray03]

Originally posted by jcayer
I thought they had AF monitors that you can buy that do just that.. they tap into the existing o2 sensor??

Subscribing and TTT for ya!:read:

Yes, there are manufacturers of guages that you can connect to the stock O2 sensors, but like I said, the stock O2 sensors are not ideal/accurate for monitoring A/F's in the 11's. If you truely want to monitor A/F then get a wide band o2 sensor and the proper hardware to monitor it. 14.7:1 is a stoich reading and the stock O2 should report .45volts or (450mv), anything higher is rich and lower is lean. They are not built to closely monitor actual A/F, only variances fro stoich. Just a little richer than 14.7:1 will cause the sensor to jump to .9v or so. I sure hope you guys arent going to gamble with your engines on that info.

 

[SnakeBit]

If you still have cats, you must put your wideband sensors in front of the cats. Monitoring it from behind the cats might tell you how good your cats are doing, but will do little for telling you what your real A/F is like. Ditto for tailpipe sniffers.

 

[BenD]

The Predator reads 02 voltage. You can hook it up and do a couple or 3 runs through the gears while a friend rides co-pilot and monitors the Predator.

If you see .90 or .94 volts then you are on the rich side. If it's down around .3, .4, .5 then you're lean.

BUT THAT'S A QUICK CHECK AND IT'S ONLY A GUIDE, I REPEAT IT'S ONLY A GUIDE! IT IS IN NO WAY A substitute for an actual dyno pull to determine your true A/F Ratio. In some cases it's way off, others it's fairly close. It's way too risky to play that game indefinitely.