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Originally Posted by dosco
How does your engine measure mass flow?
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All of the engines I've driven to sea level were IAT+MAP based 4 cylinders too old for a SG. One was a turbo. The mileage improvements were verified by knowing the typical summer city/highway mileage and the 10 gallon point on the gas gauge. The 10 gallon point is where you can read the mileage right off the odometer.
Now that my MAF based V6 no longer gets ridiculously low mileage I might take it to the sea with a Scangauge so I can get better measurements.
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A broader question is this: how are fuel maps created? Wouldn't the setup of the map depend on the sensing system?
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You'd want computers to dynamically adjust for every possible variable but unfortunately such computers would be impossible to build. The way to simplify is to test the engine under the specific conditions like IAT and come up with the simplest method for handling it. For IAT all you need to do is cut it into 10 degree Fahrenheit increments and come up with a simple formula or table for the rich factor below 60*F and above 120*F. There are 22 such increments from -60*F to 160*F which allows the entire temperature map to be held in 22 bytes plus a bit of simple code. A bit more simple code will richen more for low ECT. FWIW I am a FI computer pundit and not a designer.
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Lastly, how does the lambda sensor play into all of this?
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Between 60*F and 120*F IAT the rich factor appears to be zero so the efficiency goes up as the fuel vaporization goes up. By 100*F IAT knock starts to rise so I lose mileage if I am not careful with the pedal. The computer will provide the mixture that shows the best oxygen sensor reading unless it has other reasons to richen. Unfortunately I don't have a scope to verify that and LTFT isn't dependable enough. Sure would be nice if those new cars with the TV in dash would include an oxygen sensor scope.
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I can tell you that my 1981 Buick and my 1986 Chevy truck have WAI from the factory. My 1980 Pontiac wagon did, and I'm quite sure my 74 Chevy p/u did as well, but I had defeated it on the 74 by flipping the bonnet on the air cleaner upside down. The engine breathed a lot better,
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Carb cars had them to prevent carburetor icing and improve cold weather emissions. The two trucks in the yard are FI so don't need WAI but have it anyways. Why were WAI removed for most cars but left in for many trucks particularly when...
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They are not changing anything else- no change in driving style, no aero changes, the system is emmisions compliant. 30% FE improvement would be significant for any reasonable consumer.
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a car company could implement this in less than $100 in extra parts. Most of it would be cast into existing parts.
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and with a light foot on the accelerator got far better mileage.
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Too hot is worse than too cold. After 140*F the computer pours fuel in as a disposable coolant to save the engine and knock retards timing to gas guzzler levels.
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at least that's my un-educated shot in the dark
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Without a Scangauge that's exactly what it is. I have two nearly identical Delta 88's. Over time I have done the same mods to both cars including swapping sensors and parts back and forth to find problems and eliminate suboptimal parts. Several other similar cars are available should I suspect that parts are bad in both cars. One works so well that anyone could drive it and get averages that ridicule the EPA spec. The other gets the same good mileage when warm but knock kills the mileage when hot making the averages turn out exactly where the EPA spec says they should be. Without a SG I wouldn't even know that the mods were doing anything at all nor would I know what I need to do to get the averages up.
OP recommends that everyone with the same car needs to do the mod. If only it was that easy.