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GM NON FFV's have FFV Fuel Map

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No, you tell me how it knows the difference.

 

Lets take the case of an FFV without a fuel composition sensor running gasoline.  Assume the pressure regulator is bad, lowering fuel pressure about 40%.  The computer will need to add about that much fuel back in to keep the oxygen sensor at lambda 1.  Only now, the computer thinks it's running E85 due to the added fuel trim.  So now, the fuel and spark maps are wrong for the fuel being used, and the "check engine" light hasn't turned on.

 

Oh and Cessna, I don't think it's "our society" so much as "our government."  ;D

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I'm telling you, the oxygen(Lambda) sensor would know exactly what the proper Air:fuel ratio is whether it's in open loop or during closed loop, where it always maintains stoichemetry. If the ratio was lean due to a fueling problem the oxygen(Lambda) sensor would report a CEL for a lean condition. It's really that simple. If it's outside of the wideband range(which is limited) it'll report a CEL for out of spec condition.

 

Now if you had an exhaust leak prior to the oxygen(Lambda) sensor, that could cause a problem, maybe?

 

Edited.

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"...the oxygen(Lambda) sensor would report a CEL for a lean condition."

 

No.  You're missing a step.  The computer decides to turn on the CEL based on a predetermined set of values.  One of the big ones is if it has to add too much additional fuel (fuel trim), as determined by the oxygen sensor.

 

Therein lies the problem.  In order to get EPA certified, they have to keep that (positive fuel trim) to a minimum when operating on gas.  In an FFV that's a problem, since they need to be able to add ~40% more fuel.  Without the computer knowing what's in the tank, it could happily run along with a large positive fuel trim on gasoline, not setting off the CEL.

 

The computer is probably inferring the fuel being used based on number of sensors.  That would probably work fine, as long as everything else (injectors, sensors, etc) is in good working order.  But you could do that with a normal oxygen sensor.  ;)

 

Bottom line:  I think James is right, and we'll see a return of the fuel composition sensor.  Either that, or a disappearance of FFV's.

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I don't think it's "our society" so much as "our government."  ;D

 

The government's got nothing to do with it... cars with lots of gadgets appeal to buyers. </end-of-story>

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No, you're still not getting it. Anything above Lambda 1.0 is lean. There is no "setup" for fuel type. Stoichemetry is the same value for all fuels; gasoline, ethanol, and methanol. The purpose of a wideband is to read Lambda values outside of the narrow range of Stoichemetry, people use them for tuning because the narrow bands cannot read anything outside of Stoich.

 

The Oxygen sensor does not rely on the ECU values for it's reading.

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I don't think it's "our society" so much as "our government."  ;D

 

The government's got nothing to do with it... cars with lots of gadgets appeal to buyers. </end-of-story>

 

Yeah but that's not nearly as much fun as being paranoid of Gov conspiracies  ;D

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I don't think it's "our society" so much as "our government."  ;D

 

The government's got nothing to do with it... cars with lots of gadgets appeal to buyers. </end-of-story>

 

Yeah but that's not nearly as much fun as being paranoid of Gov conspiracies  ;D

 

I was kind of implying the whole EPA regulation w.r.t the fuel trim issue, that was being talked about...  but hey, think whatever you want.

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No, you're still not getting it. Anything above Lambda 1.0 is lean. There is no "setup" for fuel type. Stoichemetry is the same value for all fuels; gasoline, ethanol, and methanol. The purpose of a wideband is to read Lambda values outside of the narrow range of Stoichemetry, people use them for tuning because the narrow bands cannot read anything outside of Stoich.

 

The Oxygen sensor does not rely on the ECU values for it's reading.

 

No, it's you who doesn't get it.  The stoichiometric ratio is different for E85 than it is for gasoline.  E85 runs at stoichiometric at about 9.8:1 air to fuel.  Gasoline is 14.7:1.  When running with either of these fuels at their respective stoichiometric ratios, the lambda value given by the oxygen sensor will be 1, but the actual amount of fuel going into the engine will be much greater with E85.

 

The computer, which sets the injector pulsewidth, knows exactly how much fuel is going into the engine.  In order to achieve a lambda value of 1, the fuel trim needs to be higher for E85.  The reality of the situation is that the oxygen sensor doesn't have a clue what fuel you're running.  It just analyses the exhaust gas and reports that to the computer.

 

A wideband O2 sensor can be useful for running at ratios other than stoichiometric, but it cannot replace a fuel composition sensor.

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