Engine Tech Question

[99greysierra]

Hi All:

I am new to this forum, so be patient if I'm asking questions that have been covered before. I have a 99 GMC with the 4.8 liter. Since they put 10% ethanol in the darn gas my HWY MPG dropped from 20-21 down to 17.5. At $4 per that hurts !! Is there any way to reprogram the FMU to at least partially compensate for the fuel change ? Thanks in advance for any responses.

[redsled2007]

Hi All:

I am new to this forum, so be patient if I'm asking questions that have been covered before. I have a 99 GMC with the 4.8 liter. Since they put 10% ethanol in the darn gas my HWY MPG dropped from 20-21 down to 17.5. At $4 per that hurts !! Is there any way to reprogram the FMU to at least partially compensate for the fuel change ? Thanks in advance for any responses.

 

To do what? Do you want to get back to 20 mpg? Forget it. If that could be done, it would already have been done. Physics. Ethanol produces less energy than gas.

[gvbhunt]

Newer trucks have a fuel composition sensor, or at least a virtual sensor, that tells the computer what the gasoline vs ethanol content of your fuel is. Under normal conditions and running "real" gasoline your stoich AFR should be 14.68 but with 10% ethanol it should be closer to 14.03. The new vehicles will actually modify the base AFR depending on what the mixture is but I believe that yours will always stay at 14.68. Having someone change that will definately help if you have any power loss and may help a little in getting your MPG back on track.

 

No promises though.

[95Sierra2500]

Hi All:

I am new to this forum, so be patient if I'm asking questions that have been covered before. I have a 99 GMC with the 4.8 liter. Since they put 10% ethanol in the darn gas my HWY MPG dropped from 20-21 down to 17.5. At $4 per that hurts !! Is there any way to reprogram the FMU to at least partially compensate for the fuel change ? Thanks in advance for any responses.

 

To do what? Do you want to get back to 20 mpg? Forget it. If that could be done, it would already have been done. Physics. Ethanol produces less energy than gas.

 

 

You *can* tune it to get better mileage, and possibly get back to 20mpg on 10% ethanol. HOWEVER, it would be a completely custom tune and would require dyno tuning to get it right. You would, however, notice an improvement on normal gasoline as well (if you can find it).

 

Ethanol - yet another way to fleece the American Public for more of their hard-earned money.