Quote:
Originally Posted by California98Civic
"positive values indicate a lean condition exists and the injector is left open longer to compensate, thus adding more fuel" (p.17). Now that means that a UG reading of +1.56% long term fuel trim is 1.0156 lambda, a lean condition, and my car will add more fuel to maintain stoich? That's not good for fuel economy. Better would be negative percentages, indicating rich condition, in response to which the car's ECU will seek stoich by reducing fuel.
Do I have that right?
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Ideally you want to see near zero % fuel trim values on a properly operating system.
Neither rich or lean is good. Positive values indicate a lean condition as the ECU is trying to compensate for that. It is still a lean condition! Same true vica versa if it is running rich and the ECU is reducing fuel and you see the negative values, you STILL have a rich condition!
When the ECU has to exceed it's predetermined range/limit of allowed compensation in either direction,that's when you get a check engine light with the appropriate code.
(On GM vehicles I believe it is around 25% long term fuel trim value.)
Barna