Quote:
Originally Posted by Interlocutionist
I was driving today and as I was going downhill with my foot off the gas I was thinking about the pumping losses and EGR and the IAC that was probably open because the throttle was shut and I thought, "what about using the EGR instead of the IAC?"
Both the EGR and IAC bypass the throttle plate, so when coasting downhill or just decelerating, one or both of those valves have to be opened. So I was thinking, if the EGR was routed to the IAC input, or the IAC was disabled somehow and the closed-throttle airflow was all from EGR, what effect would this have and would there be any benefits or problems?
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Most newer cars will engage DFCO during heavy DECEL conditions. During DFCO the fuel injectors do not fire, so there would be no advantage to program out the throttle-follower calibrations for the IAC valve. Normally the IAC is commanded to go to full-open.
The EGR normally doesn't function during heavy DECEL. One reason is because of the lack of pressure in the exhaust during these conditions.
Each case would be different, - pressure varying with different cars and different driving conditions.
You could induce some EGR flow during DECEL by over-riding the valve, but the mass of the flow would be less than if the engine were loaded.
The catch for increasing air-flow during heavy DECEL is that most calibrations watch the MAP output to check for DFCO qualifications. If you increase your manifold pressure, then DFCO will disengage and you're back to injecting fuel.
You can get around all of this with an injector kill-switch, and simply open the throttle during coast-down.