can i drive my mk3 whit ethanol?

[grimreaper]

5 gallons of e85 with 17 of 87oct. raised my af ratio on my truck from 11.8 to 12.5. this is at wot of course, no ecu control from o2 sensor

 

[jdub]

Might want to take a look at this thread:
http://www.supramania.com/forums/showthread.php?t=67703

Figgie talks about how lambda is the driving factor for an O2 sensor...and guess what?
Stoich = Lambda 1 and it's the same regardless of the fuel used.

The stock TCCS does have limited ability to adjust AFR in closed loop...a correction coefficient of 0.8 to 1.2 to be exact. The ECU does have Learned AFR Control...it sets a learned correction coefficient over time to set injector duration to values that return the center value to stoich.

 

[supradjza80]

Wrong, O2 sensor has very little ability to trim the fuel, if you dumped E85 in your tank you'd go LEAN no matter what.

I think my post must have been unclear. What I meant was the o2 sensor is telling the ecu what the AF ratio is and the ECU trys to keep the AF in its desired range 10.5-11.5:1 (or whatever its stock desired range is) no matter if there is gas or ethanol in the fuel. So while 10.5:1 is lean for ethanol the ECU has no idea that is lean and actually thinks it is an ok or rich AF reading.

This is pretty hard to explain on a forum, for me at least.

I still dont think ethanol in the fuel will cause the AF to get leaner (move from 11.5 to 12) than pure gasoline.

 

[supradjza80]

I just looked at Figgies thread, it looks like the o2 sensor knows where stoich is for all fuels so my argument is out the window...I just learned how o2 sensors really worked.

 

[Poodles]

You're right, but only to the extent the O2 sensor is allowed to trim the fuel in the ECU. This is why the added ethanol to fuel should be fine as it's a small enough amount to just be adjusted for.

The issue is you'll make less power, lower MPG, and if your evap system is faulty the ethanol is the first part of the fuel mix to evaporate leaving you with lower octane fuel.

 

[grimreaper]

I think my post must have been unclear. What I meant was the o2 sensor is telling the ecu what the AF ratio is and the ECU trys to keep the AF in its desired range 10.5-11.5:1 (or whatever its stock desired range is) no matter if there is gas or ethanol in the fuel. So while 10.5:1 is lean for ethanol the ECU has no idea that is lean and actually thinks it is an ok or rich AF reading.

This is pretty hard to explain on a forum, for me at least.

I still dont think ethanol in the fuel will cause the AF to get leaner (move from 11.5 to 12) than pure gasoline.

im digging through my laptop for a few dynojet logs. actually lean, or just what the gauge was reading i dont know, not to knowledgeable about how the gauge would be affected with a higher then 10% ethanol content it was tunned for, although it would seem the af ratio displayed would be off yet lambada would be the same?? the wideband commander only displays for gas, with no lambada feature if that matters....

 

[turbogate]

In my situation that I mentioned earlier, I'm on a standalone with one fuel map, with O2 feedback turned off (close loop A/F adjustment). Either way, my lean A/Fs are under full load. Could that 10% ethanol be the cause of that?