Quote:
Originally Posted by ZYUL8R
Yes, the ECU gets a hot Intake temperature it cuts fuel to keep the A/F ration in place, which robs performance.
With cooler Intake temperatures it doesn't do that.
Ever notice your car running good on a cold day...its the ECU giving more fuel to burn with the denser air.
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Well....Close but......
Fuel is always being adjusted no matter what the temperature. This is handled downstream by the 02 sensors which are constantly making minor corrections to A/F based on Measured data from both sampling, and the MAF flow information. They don't care what the Intake temps are, they are just concerned with keeping things in line. There are Short term trims (imediate minor changes happening all the time), and long term trims, (that build up a reference map based on the overall conditions). Heat and IAT temps largely affect timing maps in most modern ECU's...They dial back timing as a protective measure.. The performance loss you experience is largely this adjustment. Fuel continues to be held at or around stochiometric (14.7:1 A/F) as long as you're in Closed loop mode (not WOT Open loop which uses pre-built Fuel maps and ignores 02 input). Here's an IAT and timing adjustment chart from an '08 Corvette. Notice how, at temps, over a mere 86 degrees, a timing retard starts being implemented...As a reference, it is not unusual to see the IAT's on the Z exceed 150 degrees when sitting in traffic. On the Vette chart, that's an average -6 to -8 degree timing pullback
