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I have had the Cortex 1950 for about 9 months and I have really enjoyed it. Lately I have been leaving my programmer hooked up that way I could use the different gauges that it comes with. I began to look at my 02 trim levels and two of the levels read 10.19 while at crousing speeds of around 65 while the other two levels read 99.94 at all times no matter of the speed of throttle position. I do not know much of tuning but it was my understanding that your 02 levels should read in between 0 to -1. I was told that you can reprogram your computer to say that you have larger injectors to compensate with the rich air to fuel ratio. My question is am I correct on having too rich of a air to fuel ratio and if so how do I fix this to reach the correct ratio?

-wcodyp

It displays the Short Term Fuel Trims. 1.00 is not adding or subtracting any fuel. If you see .96 or .92, this means it is adding fuel .96 = adding 4% and .92 = adding 8%. If you see 1.04 or 1.08, this is subtracting fuel 1.04 = -4% and 1.08 = -8%. This is for closed loop fuel only. The computer tries to keep the fuel at 14.64. When a certain throttle position or load is reached, the computer switches to open loop fuel and no longer uses the O2 sensors for fuel feedback. When this happens, the short term fuel values will display the commanded a/f ratio in lambda. So if it displays .86 when you go to WOT, it .86 * 14.64 = 12.59 a/f.

Thanks for the reply however I am still confused. Should I be looking at the fuel trims instead of the 02 trims to get my air to fuel ratio? And also if I figure out that I am running too rich or too lean is there a way to compensate for that using the tuner?

The O2 sensors have a voltage range from 0 to 1. 0 is lean and 1 is rich. They work on a very narrowband of 14.64. .5 volts is 14.64. This provides information to the computer to add or subtract fuel to achieve the correct air fuel ratio. The pcm can add or subtract at least 25% fuel. Now remember this only works in closed loop (idle and part throttle). As long as your O2 sensors are working correctly and you have not changed the mass air meter, you should not have to change fuel in this area.

Back to your question, there is not a wideband installed by the factory in cars. So, can you actually see the air fuel ratio? No, but you can get an idea. Closed loop fuel is always 14.64. The O2 sensor voltage tells you rich or lean of 14.64. The Short term fuel trims 1 and 2 show you how far from 14.64 in a percentage. Once you go wide open, you can only see commanded air fuel and not actual. You would need an aftermarket wideband for this.

Thank you again for the information above. I just drove my truck to see what the fuel trim percentages were and I got 18.00% for both short term fuel trim B1 and B2 howerver I got 0.0% for both long term fuel trim B1 and B2. Does this mean that I am running 18% from 14.64? And thanks again for taking time and answering my questions.

That means the computer is compensating 18% to achieve a 14.64 a/f ratio. So the end result fueling is correct. Now lets say for instance your O2 sensors are old (over 100k miles on them), they could read wrong and the pcm will compensate off their incorrect readings which will affect your air fuel. This can cause it run rich and you will lose fuel economy. The only way to really check them is to verify them with a real wideband.

Now on to the long term fuel trims. If your short term fuel trims are constantly adding subtracting fuel, they will transfer over time to the long term fuel trims. So if you are showing 18% on the short term fuel trims, it must not have been for very long, because your long term trims are at 0%. If you were at .82 on the fuel trims, this would start by going 1.04 , 1.08 and end up at 1.18 and then the short terms would go to around 1.00 again.

Alright I think that answered all of my questions. I guess that you never learn unless you ask.