14k mi later running a bit lean - Fuelly Forums

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Old 10-01-2007, 09:27 AM   #1
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14k mi later running a bit lean

My plugs have a gray residue on them, which would tell me its running too lean. That would indicate to me that the IAT resistor override does actually affect the amount of fuel injected when the engine is in closed loop, normal operation.

Otherwise, as others have said, the O2 sensors would have forced the mixture to 14.7 to 1. There is no way the plugs would have the gray deposit if that was true, IMO.
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Old 10-01-2007, 09:43 AM   #2
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What is your LED AFR gauge reading?
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Old 10-01-2007, 10:50 AM   #3
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When I had it hooked up it typically was reading a bit to the lean side
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Old 10-01-2007, 01:03 PM   #4
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If I remember right, best BSFC is like 15.5:1 or so. Can anyone else verify this?
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Old 10-01-2007, 01:19 PM   #5
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What does BSFC stand for? I just have leds, no digital readout
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Old 10-01-2007, 03:06 PM   #6
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cheapybob -

Quote:
Originally Posted by cheapybob View Post
What does BSFC stand for? I just have leds, no digital readout
I just googled this :

Simple question about gas mileage
http://www.physicsforums.com/showpos...5&postcount=14
Quote:

krab,
The efficiency is nowhere near a constant. If you look at p. 27 of http://me.queensu.ca/courses/MECH435...erformance.ppt, you'll find a contour plot of specific fuel consumption versus engine speed and torque (sorry I couldn't find any links to this type of image on its own).

Fuel efficiency is

Attachment 959fuel density (a constant), F is the force required to keep the car at speed, and bsfc is the (brake) specific fuel consumption (mass of fuel per time per power delivered).

As you've said, F=F(v) is a monotonically increasing quadratic. But bsfc depends on both engine torque and engine speed. These can be related here to F and v by numbers which change only with the chosen gear. In a fixed gear on level ground, the bsfc can therefore be read off the graph by finding the intersections of the contour lines with an increasing polynomial. Depending on the details, this is likely to change quite drastically with speed. And that change is not monotonic.
I don't know what most of that stuff above is, but I think it has to do with engine operating efficiency.

EDIT : I think BSFC Maps are those graphs that look like "topo maps".

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Old 10-01-2007, 06:05 PM   #7
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I am trying to find this information for my motor (M103) in my 190e, and about all I found (in Thai) is .5LB/HP/hr...does this sound right??
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Old 10-01-2007, 09:54 PM   #8
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so, then it looks to me he's saying you get the most out of the fuel at a 15.5 to 1 ratio, which would partially explain why I'm getting better mpg running leaner than 14.7 to 1.
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Old 10-02-2007, 11:47 AM   #9
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cheapybob -

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Originally Posted by cheapybob View Post
My plugs have a gray residue on them, which would tell me its running too lean. That would indicate to me that the IAT resistor override does actually affect the amount of fuel injected when the engine is in closed loop, normal operation.

Otherwise, as others have said, the O2 sensors would have forced the mixture to 14.7 to 1. There is no way the plugs would have the gray deposit if that was true, IMO.
Have you disabled your hot air intake during this 14k run?

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Old 10-02-2007, 12:16 PM   #10
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Quote:
Originally Posted by cfg83 View Post
I don't know what most of that stuff above is, but I think it has to do with engine operating efficiency.

EDIT : I think BSFC Maps are those graphs that look like "topo maps".

CarloSW2
It's pretty much this...

The BSFC contours are the ovals w/ the numbers and the "Road Load 4th Gear" line is the "increasing polynomial" associated with fourth gear and this car/engine. A taller Fourth would result in a Road Load line that started higher and is steeper, exiting the oval at a lower engine speed, meaning the car's top speed would be limited by available power, not gearing, while running through a set of ovals with lower BSFC values, meaning the engine will operate more efficiently in the taller fourth. Not all engines can benefit from a taller OD gear ratio when cruising, but IME most can, provided the driver can control the transmission.
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