Flex Fuel Caravan Question
Flex Fuel Caravan Question
(OP)
Does anyone know how the 2000 3.3L Flex Fuel Caravan detects the amount of Ethanol in the gas tank? I heard some cars just use a Lambda sensor to detect the amount of Ethanol. I'm not sure if that is done with a narrow band oxygen sensor or if it necessitates a wide band oxygen sensor. The other method I heard of was to use a fuel sensor that can detect the dielectric strength (if I remember correctly) of the fuel mixture to determine how much ethanol is present.
Thanks!
Thanks!





RE: Flex Fuel Caravan Question
RE: Flex Fuel Caravan Question
RE: Flex Fuel Caravan Question
RE: Flex Fuel Caravan Question
RE: Flex Fuel Caravan Question
This will occur regardless of the fuel's stoichiometric air/fuel ratio, as long as adjustment is within the control's calibrated range.
If you have a way of biasing the apparent switching point of the signal sent to the control, the end result will be the same regardless of the fuel. If the control is very rudimentary (unlikely), you may succeed in shifting the calibration lean. However, I suspect there are catalyst diagnostics that will be triggered, resulting in illumination of the CEL, and possibly disabling closed loop control. At that point you're probably worse off than when you started.
Running "a little leaner than stoich" might provide a measurable increase in fuel economy. A catastrophic increase in emissions is guaranteed.
RE: Flex Fuel Caravan Question
I argee that the NOx emissions will increase with a leaner AFR but, wouldn't the rest of the emissions (HC, CO) go down because less fuel is being consumed?
RE: Flex Fuel Caravan Question
Feedgas temperature into the catalyst will go down, which may reduce conversion efficiency of HC.
RE: Flex Fuel Caravan Question
RE: Flex Fuel Caravan Question
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RE: Flex Fuel Caravan Question
That is my assumption. Why do you think advancing the ignition will loose any gains from running a lean mixture?
RE: Flex Fuel Caravan Question
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RE: Flex Fuel Caravan Question
I'm not talking about advancing the timing on a stock setup. I'm talking about advancing the timing on a modified lean burn setup.
RE: Flex Fuel Caravan Question
If about stoich needs say 25 deg advance to give peak cylinder pressure at 14 deg ATDC, and you lean it off say 10% and get a slower burn, two things will happen.
1) You will need wider throttle to get the same power, say 7% more airflow, so 7% of the 10% saving is already lost.
2) as it burns slower, you need say another 5 deg advance to get peak cylinder pressure t 14 deg ATDC. That means the piston is moving up against a burning charge for 5 extra degrees, all happening when the rod angle is effective at using that pessure to work against the piston moving up. ie it takes more power from the crank to work against the expanding charge on the compression stroke.
Net result is most likely a negative.
I expect there will be a sweet spot where combustion pretty well completely consumes the fuel, but burn rate is not greatly reduced. That will be very close to where conventional wisdom gained by years of experience already has it.
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RE: Flex Fuel Caravan Question
1) You will need wider throttle to get the same power, say 7% more airflow, so 7% of the 10% saving is already lost.
The wider throttle opening does result in less pumping losses. This will add a little bit to the savings. I don't know how much but I do know Diesels are a lot more efficient for that exact reason.
On your second point you said,
2) as it burns slower, you need say another 5 deg advance to get peak cylinder pressure t 14 deg ATDC. That means the piston is moving up against a burning charge for 5 extra degrees, all happening when the rod angle is effective at using that pessure to work against the piston moving up. ie it takes more power from the crank to work against the expanding charge on the compression stroke.
If the charge is burning slower you will not have more pressure at TDC. You will have the same pressure as before. It just took longer to get there. The crank angle is a good point, though. The 5 extra degrees of crank angle rotation is happening when the air/fuel charge first sees the spark. The burn rate at this point of time is much slower than when the cylinder is at TDC and after TDC. The added pressure due to spark advance against the connecting rod during those first 5 degrees is probably very low.
Great points. I could be wrong, but that is why I am asking the question.
Just a side note, I don't mind losing power due to a lean burning setup. I'm not looking to make the same horsepower as my stock setup. I don't care about accelerating hard. I'm just concerned about fuel economy. What I don't want to do is loose out on fuel economy because the engine wasn't running efficiently due to the spark advance being off.