Quote:
Originally Posted by mechman600
A bit of a side note. Unplugging the intake manifold temp sensor and installing a resistor to make the ECM think it's cold advances the timing on some engines and does wonders for mileage. I repeat: SOME engines. Cat engines: 100 ohms = indicated 7F. Cummins I'm not sure, but I could easily find out.
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I can believe this. It's a cold start up feature. During cold startup (or extremely cold conditions) the ignition delay increases, thus the injection timing is advaced to prevent the combustion from occuring too late in the cycle. In extreme cases this late combustion can cause white smoke or misfire. The ECM is using the IMT sesnor to detect this cold condition.