What Data is Good Data?

What Data is Good Data?

A common thing people can get hung up on with tuning their cars today. What data is good? What data is bad? And what data is good, and telling you something else is bad! Sounds confusing right? It’s not, you just need to know what to look for, why the data looks the way it does, and how to know when there is a problem. Let's dive right in and see what good data looks like.

Take a look at these Key On, Engine Off (KOEO) values below. This is what you would typically see for good data. Notice things like MAP, MAF, ECT, IAT, and even HO2S (Oxygen Sensor). The MAP should read between 95-105 in most cases, your MAF should read zero volts, or zero Hertz, ECT and IAT should be close to ambient temp if you have not run the vehicle in a few hours. Your HO2S’s should be at or very close to 450 mV.

Now let’s take a look at some Key On, Engine Running (KOER) info. Take a look below at some good data. Notice when running at idle the MAP sensor is reading 30-50 KPa range, this is typical of most engines, if you have a larger camshaft, expect something more like 40-60 KPa. watch your MAF, did is rise in voltage or Hertz when you started it? The MAF numbers can change greatly depending on application. More what you need to look for is look for the numbers raising, they should rise with RPM for the most part. You will find during WOT they may start to even out at some point. Easy ones, ECT and IAT should rise with engine temp and under hood temps. Your ECT should rise to operating temp, anywhere from 180-220 depending on application and cooling system components used.

Lastly, my favorite is the oxygen sensors. Pay attention to your Bank 1, Sensor 1 and Bank 2 Sensor 1 Oxygen sensors.  These are your pre catalytic converter sensors used for fuel trims. They should toggle consistently. Going from 100 mV up to 900 mV.

Take a look below, you will see the MAP in Purple, able to move as load moved, airflow raised as RPM did, and the HO2S’s are toggling up/down as they should. This is a great example of what good data should look like.

Ok, so now we know what good data looks like, let's take a look at some bad data. MAP sensors reading close to 95-105 KPa the entire time, you may have a vacuum line to it not connected, the sensor may be faulty, or possible an electronic circuit fault. Moving forward into the MAF sensor, you should see a steady increase in numbers whether Voltage or Herts as RPM raises and more airflow enters the engine. If the numbers to not raise at a steady rate, you may have a dirty MAF sensor, which is very common. If the number never move, you may have a faulty sensor or electrical circuit.

On the temp side of things, it's pretty simple. They generally do, or don’t work. If you have an ECT or IAT reading numbers like -40* Fahrenheit, suspect and open circuit, such as bad sensor, unplugged sensor, or problems with the electrical circuit. If you see issues such as temps reading very high all the time, such as 285* Fahrenheit, you may have a shorted circuit. Commonly a bad sensor or a bad electrical circuit.  

Onto the Oxygen Sensors (HO2S). In general, you should always see the HO2S’s toggling up/down. If you have one stuck low, such as maybe 200 mV, that's not saying you have a bad HO2S, it's possible it's telling you there is a lean condition present. Reverse of that, if you have HO2S data of 800 mV all the time, you may have a rich condition present. So, with these sensors, you may see voltages we do not find acceptable, but they are simply doing their job, and telling us there may be an issue. If you find an HO2S that never moves, and is always stuck at or around 450 mV, then you might have a bad, unplugged or circuit problem. When your data sits at 450 mV, that is a base voltage input via General OBD2 data and will not change.

As you can see above, most of the data looks great. Is there a bad sensor here? Most likely not. The sensors are simply telling there is a rich condition present. Always remember, low HO2S data (Under 450mV) is indicating lean, and high HO2S data (Over 450mV) is indicating a rich condition.

We hope this helps next time you may run into a small snag in your tune. Thanks for reading and stay tuned for more!

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