Quote:
Originally Posted by UFO
"Coasting" in gear is not coasting. That is called engine braking.
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Thanks UFO. I should have said such, and actually did so in my email to Linear Logic. Interestingly, the rep called that coasting...
One of few links I saved:
Looks like I cannot provide links at this point (need 5+ posts). Here is the content:
"No. Wrong.
All modern electronic fuel injection systems that I am aware of (and that includes a very large percentage of the market here in the US) shut off fuel on deceleration. The reason for this is NOT fuel savings, it is for emissions. Cars nowadays have to meet some very serious emission requirements. Leaving fuel injectors on during deceleration gives no advantage.* They also have a very serious disadvantage in that if you leave the injectors on you then have to deal with unburnt hydrocarbons, and CO.
This is why Bosch K-Jetronic fuel injection went the way of the dodo bird. The K stood for Konstant, this system just pissed fuel into the engine if there was air coming in. Because it sprayed fuel all the time air was flowing into the engine, it was too dirty to meet newer emission requirements.
As far as the details go, typically the system will look at throttle position (duh!) engine temp, and possibly air temp. If the throttle is closed above say 2,000 RPM the ECU stops activating the injectors until a preset RPM is reached, and then they are turned back on. This cut in RPM might be about 1300 RPM warm, and somewhat higher cold, say 1800 RPM. If the driver steps on the gas, the injectors resume right away, regardless of engine speed. This off and on function of the fuel injectors is imperceptible to the driver, but can be demonstrated in a shop using shop tools. I have shown this to my students hundreds of times.
I am not sure of the first system that used fuel cut, but I know Volvo has used it since mid 1982.
Getting back to the OP, assuming your ECU used a fuel cut strategy the difference in fuel usage would be so small I doubt you could measure it. But leaving the car in gear and allowing it to coast would use less fuel on a modern engine. I am not familiar with your model car and engine, so I do not know if uses fuel cut. I suspect it does, but I am not sure.
*The only advantage of leaving the injectors on, is it will keep the engine temp up. If you descend a very long grade, it is possible to have the engine coolant cool off to the point that the heater stops blowing hot air. This complaint shows up during the winter at some car dealers in Denver after cars descend the Eisenhower grade."
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So, if I decide to do my downhill coasting in gear, ie engine braking, is getting TPS out of gear, idling, desired, then adding 3 or 4? As opposed getting a TPS figure while engine braking...
Thanks much.