Does anyone happen to have a chart showing NB O2 sensor voltage vs. fuel mixture for various amounts of ethanol in the fuel. In Texas we are getting E10 now for everything. I have a feeling that even at the E10 level, it is playing with the oxygen sensor voltage output. My thinking is that it is decreasing the voltage output, making the engines run richer and even setting TOO LEAN codes in some instances.

Does anyone happen to know the ideal O2 sensor target voltage for stoichiometric operation on E10?

 

We have the 10% mixture here on the east coast, too. The stations that carry it always overcharge for it.

Really, the O2 sensor should target stoich, so its output shouldnt change too drastically with the added ethanol. The only thing you should really notice is the BLMs rising to compensate for the ethanol. The new stoich value will be around 13.8 or so for the blend, in theory. Id guess that potentially, depending on how things are set up and how the tune is, that could cause a code to set.

 

I am not really having too much of a problem with my TBI's. It is my Vortecs, my Vortec TPI, and alot of newer fords.

 

It's not "playing" with the voltage, i.e. it's not poisoning the sensors, it's just as dimented says, where it's a different fuel that requires a different air fuel ratio to burn stoichiometrically. The ECU has to add fuel to get to stoich, from the pre-programmed 14.63 for gasoline to whatever it takes for E10. If that's too much compensation for the OBD functions, it may say it's too lean, especially if it's combined with other wear and tear and tolerances.

Oxygen sensors are just oxygen sensors (with small catalysts on board). Stoichiometric is just stoichiometric, which varies from fuel to fuel. When an engine is rich of stoichiometric, the oxygen sensor generates a voltage greater than 450 mV, lean it doesn't.

The ideal switchpoint may vary with your choice of catalyst, and the load, and the emissions balance, but the general center will be dependent on the O2 sensor, not so much the fuel.

 

1) A NB is a switching type sensor. There's no correlation on it's output other then rick or lean of Stoich.

2) Nope, the O2 is working on what is Stoich, it doesn't care what fuel you're using. Unless the fuel takes more (less) fuel to get to stoich then the BL limits will allow.

3) The cross over voltage from rich to lean (based on Stoich) is a constant.

 

Innovate Newsletter:

Tuning Tip: Ethanol Content

We've had a few reports where users could not “nail down” their tune on the street with the LM-1. The AFR's would jump about 0.5 AFR across the WOT band even in the same weather conditions in the space of a few days. Instead of holding a tune, the engine seemed to slowly “yodel.”

Naturally the first thing to blame was the LM-1. But it turned out that the users filled up at different gas stations, sometimes filling up on gas that had 10% ethanol mixed in. As expected, when Schnapps is mixed with cars, things get a little complicated.

If ethanol (stoich AFR of 9) is mixed with gasoline (stoich AFR of 14.7) the resulting gas has a lower stoich AFR than 'pure' gasoline. As the fuel injection is tuned to mix a certain amount of fuel for a given amount of air, the resulting mixture would be leaner when using a fuel with lower stoich AFR.

This can be calculated:

sAFR = (%ofAdditive * sAFRadditive + (90-%ofAdditive) * sAFRgas) /100

where:
sAFR is resulting stoich AFR
%ofAdditive is amount in % of mass of additive (ethanol) mixed in
sAFRadditive is stoich AFR of additive (9 for ethanol)
sAFRgas is stoich AFR of base gasoline (14.7)

For a 10% mixture of ethanol to gasoline by mass the resulting stoich AFR is 14.13

So, for an engine that's tuned to certain AFR at a certain load and RPM on straight gas, the resulting (gasoline equivalent) AFR when running the mixture can be calculated as:

new AFR = tuned gas AFR * (gasoline stoich ratio) / blend stoich ratio

An engine tuned to 12.5 gas AFR will run at the equivalent of 13 gas AFR with a 10% ethanol blend. This is what these people were seeing.

Of course, when running in closed loop, the engine will run at 14.13 AFR instead of 14.7. O2 sensors (incl. widebands) don’t measure AFR, but Lambda. Lambda is defined as actual AFR/stoich AFR. It's a ratio. In closed loop part throttle the engine is just running at Lambda 1.0, regardless of fuel. The same would be true for other Lambda values when running closed loop at WOT using a wideband. The engine would run at the tuned Lambda and everything would be fine. Open loop systems would need to be retuned for alcohol blends though.

Until next time... Keep On Tuning!

-Innovate Motorsports





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Thanks for all the info guys.

Sounds like I just need to put the stoichiometric ratio at 14.13 and leave the O2 table where it ran best on "normal" gasoline.

 

Thanks for the info as well. This post should be made into a sticky and the post link should be added to the tunning guide book well....