This year after May, gas is no longer to contain MTBE as an octane enhancer.
What are different brands doing to enhance octane in place of it? One way is the 10% alcohol blend that is showing up here in Houston. I mostly use Chevron, and recently they have posted signs on their pumps stating that their gas may contain up to 10% ethanol.

For years my car had been running the AFRs that I had tuned for. But since May, I noticed that my smooth lean idle became rough. I had to add 3.5% more fuel to get it to smooth out again. If 10% ethanol is added, it will lean out AFRs due to it being less dense.

To test this, I added 3.5% more fuel to my boost area for over 10PSI. Then I went
logging with my wideband and DATALOGIT. With the additional 3.5% more fuel,
my AFRS are what they were last fall when I last logged AFRs.

If you are running 11.2 AFR for 14PSI boost like I am, this new ethanol induced 3.5% leanest; is leaning it out to 11.6 AFR.

This could be bad for your engine!

 

YIKES! Good info.

 

Here is a USA fuel formulation map from Exxon dated May 2006.

http://www.exxon.com/USA-English/Fil...p%20100102.pdf

RVP info: http://www.eia.doe.gov/oiaf/servicerpt/fuel/rvp.html

If you drive into another area, it could affect your engine!

 

We've had that here in Vegas for years.....sucks

 

Good info, Chuck! That's enough to make the difference between running safe and getting dangerous!

I'm glad Pensacola is still on good ol' plain gas . But, this is REALLY good to know if you travel!

Dale

 

im still waiting for E85 to availible.