shows what happens after ECM shifts Long FT to +10%. Although MAF and rpm remain the same, basic injection increases by 10% based on shift in Long FT. Basic injection is now 3.3 ms.

• The fuel system is now supplying enough fuel to restore nearly normal oxygen sensor switching. Switching is taking place but the voltage swings are lower than normal. Short FT is still making an excessive correction (+15%) to achieve this.

• ECM learns that it must continue shifting Long FT to get Short FT back to ±10%. Condition #4

shows the result of another shift in Long FT. MAF and rpm are still the same as in condition #1, however, basic injection duration has increased by 20% to 3.6 ms.

• Basic injection is now back within ± 10% of required injection.

• Normal oxygen sensor switching is accompanied by Short FT switching ± 10% of basic injection duration.

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