Higher BLM with 10% ethanol gasoline?????

[slipstick]

I have been chasing the cause for higher than normal blms in my '87 GN. Most cells will go to 136-137. I have NO vacuum leaks and I have changed the O2 sensor. The driveability is fine. However, something has changed slightly in the last 6 months or so. I learned last week that the gasoline I have been using could contain up to 10% ethanol. I know that in carb cars the jets must be increased when using ethanol and I suppose gasoline with a percentage of ethanol would require some percentage of increase in jet size. Now, my question could the higher (higher than my normal) blm numbers be a result of the computer adding fuel (through the O2 sensor input) to compensate for the 10% ethanol in the gasoline??????

 

[JDEstill]

If I did my math right, you need 4.1% more fuel to get to stoich with E10 than you do with straight gasoline. So if your car was set up to where it achieved a BLM of 128 on straight gasoline, then you would expect the BLM to jump up to 133 when fed an E10 blend.

John

 

[slipstick]

So does the logic that my higher blm numbers may be the result of my current gasoline containing 10% ethanol seem reasonable???????????????

 

[GNVYUS 1]

Yes, this is why the E85 guys have to add around 30% at WOT.

No biggie, 1 or 2psi of fuel pressure will probably do the trick.

 

[BASS]

Hmm, very interseting. I got the same problem, my idle blms are at around 133-135 with all this 10% ethanol crap gas here in NJ.

I have no vacuum leaks that I can find, and no exhaust leaks before the turbo to cause this high blm. I have eric's 93 tt chip, and was wondering if he burns the chips to run strictly on straight gasoline? If so, I guess I need to increase the fuel % on the chip (because Ive been chasing down a 3rd gear knock problem forever!)?

 

[slipstick]

Thanks for the replies. I like knowing cause and effect. Things like this drive me nuts.

 

[mikestertwo]

So does the logic that my higher blm numbers may be the result of my current gasoline containing 10% ethanol seem reasonable???????????????

I have seen this on my Buick and Cadillac. The ethanol raises the O2 level in the exhaust which tells the computer you have a lean condition so it adds fuel. One reason the gas mileage drops with the alcohol blend.