Hummer Forums by Elcova

Hummer Forums by Elcova (http://www.elcovaforums.com/forums/index.php)

- Technical Discussion and Customizing your H3 (http://www.elcovaforums.com/forums/forumdisplay.php?f=26)

- - MPG (http://www.elcovaforums.com/forums/showthread.php?t=19301)

I am getting anywhere from 11 to 13.5 miles per gallon. I do almost all city driving. That seems a bit low.

What are you guys getting? (city driving?)

try a search, MPG has been discussed many times

I get around 18 on highway and 15 to 17 around town.

14.1 is the lowest I've seen with my H3 so far in 13 months.

S.

Take it out of 4lo. ;)

Quote:

Originally Posted by f5fstop

try a search, MPG has been discussed many times

oh well....you tried:rolleyes:

My mpg is in your range.

Plus Bebe, I need to get to 1,000 posts :D
Would have been there, but lost around 200
when we moved to the new site here.

I ran premium for the first 11 months and 9,200 miles. Diligently checked mileage at each fill-up and made between 13 and 18 mpg, depending upon what conditions I was driving. The 18 was almost all on the 1,000 mile trip to Cabo. Since then, I have a short daily commute here and do quite a bit of beach and sand driving and am certain that is the reason for my somewhat lower mileage than most others have experienced.

After reading the many posts regarding the no risk of switching to regular unleaded, I grudgingly decided to test it out. I have had bad experience with regular, as my 1995 Bronco shows way worse performance using it. It performs with lower mileage and way lower power using regular unleaded.

However, the H3 shows the same mileage using regular unleaded or premium - 14.5 on the first tank and 15.1 on the second tank with no noticeable power difference.

In the other posts on this forum it is discussed (by some knowledgeable people) that the timing in the H3 engine automatically adjusts and compensates when lower octane fuel is used. So, I didn't want to believe it, but it is really true and now I save 10-15 bucks per fill-up.

If you sift through the BS (and all the fun), there are some extremely helpful nuggets of wisdom to be found on this site.

System cannot detect for NO knock, it can only detect knock. Hard to explain this...
Let's say the base tables are set for a specific octane, as long as you use this octane and do not experience any knock, the PCM does not need to change timing. If there is knock detected, the PCM will adjust the timing curve to get rid of the knock.
Basically, the PCM does not know what fuel grade you are using, it is only interested in if it is causing knock. (It's early)

I am averaging about 16.5 with 75% City driving, using 87. Are you flooring it at each stoplight?

Quote:

Originally Posted by lance-n

The H3 has two spark timing tables - high octane and low octane. The data in 2D tables are arranged by RPM and cylinder airmass. The PCM starts on the high octane table and if knock is detected reduces the timing until knock is gone. The working timing table usually falls in between the high octane and low octane tables. However, the H3 is the only vehicle that I have seen that primarily stays on the high octane table which means there is no room for timing advance to take advange of higher octane gas. This is why you don't feel a power/MPG improvement with the higher octane gas.

see lexunet, these guys are great!

maybe the reason you are getting poor mileage is that you neglected to tell us you are running around town with 35" M/T's at 18 psi, that should put it down around 11 mpg!

Quote:

Originally Posted by ChevyHighPerformance

Are they using a wideband knock sensor on the I5?

Michael