jmrussell89

Curious to see if anyone else is having these issues.

I recently had my car tuned, and the tuner used his own system for reading the AFR (o2 sensor up the pipe). The car has been running great, but really getting on it, I've noticed the gauge is reading 10.0-10.2. The dyno sheet shows the normal 11.3-5 or so, and the car isn't showing signs of running to crazy rich. However, the car idles at 14.7-15.1 which is pretty normal obv.

Do these gauges really have that much of a margin of error or have I managed to do something to cause this condition? It's tuned on SD.

evo8426

iTrader: (27)

Where is your sensor located? If the gauge is installed correctly and not had any damage I would trust the one that is in the car more than one stuffed in the tailpipe on the dyno.

RightSaid fred

They're accurate at lambda 1.
They're also accurate at the 20 to 1 end of the scale.
They're NOT accurate at the 10 to 1 end of the scale.

All WBs are the same unless you've calibrated it against a 5 gas analyser or dyno flow meters or both.


If you're taking a reading after a catalytic converter (tailpipe) they're even less accurate , it'll read leaner than actual.

Tsi2Evo6

One other thing to keep in mind is that the wideband on the car is not pressure compensated. They will read up to 1 afr richer then if you measure from end of tail pipe as long as you don't have an exhaust leak.

4b11slayer

Have you looked for vac/boost leaks. Or exhaust leaks?

RazorLab

iTrader: (8)

Through all my years (twenty plus years) of dyno and street tuning, using a good tailpipe clamp (Innovate), I have never seen it one point richer or leaner at the tailpipe compared to a wideband in the downpipe or test pipe. At WOT they are 98-99% the same.

Tsi2Evo6

I should have been more clear. In my experience at higher boost levels 28+ psi if the customer has a full exhaust the gauge would read slightly richer then tail pipe. 1 afr lower would be an extreme case (small exhaust, high boost). That's why sensor position is so important. I'm sure it's why you've never experienced it. This also verified by Bosch and NGK.

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RightSaid fred

You're NOT going to know if you don't also have a 5 gas exhaust analyser running alongside.
Then as a third check you use the flowmeters on the engine dyno to measure both the mass of air and the mass of fuel.
That gives you 3 different AFRs, all at the same time.
The WB is always the odd one out.

WBs haven't been around for 20 years, only about 15.
20 years ago everyone was tuning with NBs.


You've probably got the usual SD fails.


It's called SD for speed density.

That means that the tables you use for tuning have an x axis and a y axis.

One axis is speed (RPM)
The other axis is manifold density.
NOT manifold pressure.
Density has to be calculated by using the MAP sensor (pressure) and AIT sensor mounted IN the manifold (temperature).
Temperature and pressure taken at the same point make density.
No other way does.

If your sensors give out wrong signals due to being mounted in the wrong place and measuring the wrong things , then you'll end up with a variable tune which changes with the weather and changes with driving conditions.

That's why it's called a "patch".
Because it's not as good as the real thing.