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Old 03-02-2011, 12:52 PM   #6821
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Yeah, but I think his question (and I want to know too) is how exactly do these things actually work? What is the mechanism by which they judge the composition of the fuel? Do they run it between two plates and measure the effective capacitance? Do they pass it through a chamber containing a small amount of americium-241 and measure the rate at which some element in the fuel bonds with the ionized nitrogen atoms generated by the slow alpha decay of the source? Do they use it to lubricate a tiny pink ***** and have a tiny little man constantly describe the relative lubricity as the ***** is repeatedly inserted and withdrawn from his tiny little anus?
This.

That page was a good read, and I discovered that the GM fuel sensors actually measure both ethanol percentage as well as fuel temperature, but I'm still curious how it works. The article seemed to hint that perhaps it's measuring oxygen content (that is, the oxygenated fuel) to determine ethanol percentage, but I still don't know how that is actually measured.
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Old 03-02-2011, 12:53 PM   #6822
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Originally Posted by rider384
Quick question: If I tune my car for E85 and want to switch back and forth between 91 and E85, will I have to drain the tank going from E85 -> 91? I know I will when I go from 91-> E85, but what about from E85 to 91? EDIT: I guess the real question is wheather or not I can switch to 91 with like 1/4 to 1/8th a tank.
When I used to switch between the two I'd always try to run the tank down to the last gallon or so of fuel (in a Talon...16gal tank), so the mix was relatively innocuous with respect to the ratio. I never had an issue with either tune on my dual map setup when I approached it this way.

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Do they use it to lubricate a tiny pink ***** and have a tiny little man constantly describe the relative lubricity as the ***** is repeatedly inserted and withdrawn from his tiny little anus?
This is the method. I've seen a pic somewhere...I'll post it if I can find it again.
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Old 03-02-2011, 01:15 PM   #6823
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Ok, serious time. Some research into the subject has produced a couple of interesting datapoints.

First, my first guess (which was actually intended to be sarcastic) was right. At least some of the sensors are capacitive in nature, using the fuel as a dielectric. Specifically those supplied by Siemens and Delphi are of this design, which are apparently the ones used by GM. There are some newer designs which are refractive in nature, but I find no references to their actually being used in an OEM application. Source: http://www.eng-tips.com/viewthread.c...=161127&page=7


Second, it would appear that these sensors are unreliable as hell. Lots of complaints on E85 forums about them failing. Apparently, the situation is so bad that people are now building "sensor replicators" that simulate the signal produced by a tankful of conventional E10. This eliminates the ability to run E85, but folks don't seem to care. Here's a link to one such product: http://www.tandselectronics.com/


Third, GM doesn't use fuel composition sensors of any kind anymore. Instead, they're doing the analysis purely in software (the call this V-FFS) using the primary O2 sensor and a lookup table which compares expected injector durations to various fuel compositions. In other words, the ECU knows that, at a given load condition, it should take xx milliseconds of injector duration to produce 1λ on gasoline, and yy milliseconds to produce 1λ on E85, so by looking at what the actual injector duration is at a point in time when the O2 sensor is giving a stable reading of exactly stoichiometric, it can make an educated guess as to what the fuel composition is.

Sources: http://www.autos.ca/auto-tech/auto-t...ex-fuel-system
http://www.gm-trucks.com/forums/inde...howtopic=52132

Clever.

I wonder if the MS3 inner-circle is cognizant of these facts?
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Old 03-02-2011, 01:25 PM   #6824
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Third, GM doesn't use fuel composition sensors of any kind anymore. Instead, they're doing the analysis purely in software (the call this V-FFS) using the primary O2 sensor and a lookup table which compares expected injector durations to various fuel compositions. In other words, the ECU knows that, at a given load condition, it should take xx milliseconds of injector duration to produce 1λ on gasoline, and yy milliseconds to produce 1λ on E85, so by looking at what the actual injector duration is at a point in time when the O2 sensor is giving a stable reading of exactly stoichiometric, it can make an educated guess as to what the fuel composition is.

Sources: http://www.autos.ca/auto-tech/auto-t...ex-fuel-system
http://www.gm-trucks.com/forums/inde...howtopic=52132

Clever.

I wonder if the MS3 inner-circle is cognizant of these facts?
I wonder how immediately it applies that change -- real-time data from the O2 sensor, I know, but how rapidly does it modify the fueling?

Hypothetically, if you shut it off running 100% gas (ethanol-free), and then emptied the tank and started it up on E85, how many combustion cycles would occur before the fueling was adjusted to the appropriate level?
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Old 03-02-2011, 01:42 PM   #6825
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As soon as the residual fuel is out of the lines, rail and injectors and burned. Pretty quick I'd say. Unless you meant that by draining the tank.
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Old 03-02-2011, 01:47 PM   #6826
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As soon as the residual fuel is out of the lines, rail and injectors and burned. Pretty quick I'd say. Unless you meant that by draining the tank.
Right, but how many combustion cycles will have occurred by the time the O2 sensor has measured the change and adjusted the fueling?
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Old 03-02-2011, 02:08 PM   #6827
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Right, but how many combustion cycles will have occurred by the time the O2 sensor has measured the change and adjusted the fueling?
Probably several hundred or several thousand, if I interpret what little information is available correctly. Of course, I expect that feedback from the O2 sensor and knock sensor would at least get the engine "roughed in" prior to actual recalibration, and perhaps a large detected variance in gEGO or gKNOCK is enough to initiate a recalibration by itself?


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Hypothetically, if you shut it off running 100% gas (ethanol-free), and then emptied the tank and started it up on E85, how many combustion cycles would occur before the fueling was adjusted to the appropriate level?
This is an interesting question. If I interpret the information I have found literally, the system would not recalibrate at all unless you filled the tank to a higher level than it had previously been filled with prior to being drained. I'm sure there must be some method for dealing with the contingency, but I've not seen it specifically enumerated.
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Old 03-02-2011, 03:02 PM   #6828
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Old 03-02-2011, 03:54 PM   #6829
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Old 03-02-2011, 04:03 PM   #6830
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That was awesome. I would have drove along side of them longer to get more footage. What are they gonna do, get me?

Related video -

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Old 03-02-2011, 04:05 PM   #6831
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"Mommy, why don't they make a Barbie like me?"
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Old 03-02-2011, 04:13 PM   #6832
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"Mommy, why don't they make a Barbie like me?"
"Sorry honey, real girls walk on the floor with their feet. They don't scoot around using their fat layers like a blob".
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Old 03-02-2011, 04:15 PM   #6833
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I swear, if one more person posts advice on my thread about Rotrex with stories that pertain only to roots blowers....
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Old 03-02-2011, 07:13 PM   #6834
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what is the average price to get a rear axle fixed in a older truck... say a 1986 ford bronco?
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Old 03-02-2011, 08:30 PM   #6835
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I don't know. Don't you work for NERV? Ask Balthasar or something.

Seriously though got pics of your Auska ex gf? Plez
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Old 03-02-2011, 09:30 PM   #6836
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I got banned from CR for a week. WHAT WILL I DO?????
Apparently it's unacceptable to tell somebody to army crawl through a razorblade factory then swim in a pool of AIDS. ****** crybabies
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Old 03-02-2011, 11:51 PM   #6837
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god dammit faeflora... god dammit.
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Old 03-03-2011, 12:24 AM   #6838
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What was that retarded magazine that decided to turn a Miata into a racecar so they bought a 600 dollar eBay turbokit and a 1.1k 5Zigen exhaust?
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Old 03-03-2011, 12:48 AM   #6839
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What was that retarded magazine that decided to turn a Miata into a racecar so they bought a 600 dollar eBay turbokit and a 1.1k 5Zigen exhaust?
All of them.
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Old 03-03-2011, 08:19 AM   #6840
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