This Just In... All 2008's must run PREMIUM!

[jmsspratlin]

[Tex_h2]

For 11 years I ran 93 octane in my truck, and now with a jet chip I still run 93 octane..(actaully have to) Some say it doesn't matter, some say it does....I think it does matter.....

[Agriv8r]

Originally Posted by Tex_h2

For 11 years I ran 93 octane in my truck, and now with a jet chip I still run 93 octane..(actaully have to) Some say it doesn't matter, some say it does....I think it does matter.....

if you dont change it how do you know....

[mikejr]

Originally Posted by Hummer Guy

I don't think higher octane would smooth the idle, but I agree that 2008 models idle a little rougher. The exhaust, to me, sounds a lot better too (more aggressive), and that's just one of the 'downsides' to having the bigger, nearly 400 HP engine in the '08

I remember when they bumped up the HP in the avalanch from 2003 to 2004 it idled rougher too.

I agree with you, that exhaust sounds AWESOME....thats probably why I am only getting 10.7 MPG, I keep putting my foot into it to hear that rumble. It is sweet sounding.

Mike

[BigBlue]

Originally Posted by mikejr

I remember when they bumped up the HP in the avalanch from 2003 to 2004 it idled rougher too.

I agree with you, that exhaust sounds AWESOME....thats probably why I am only getting 10.7 MPG, I keep putting my foot into it to hear that rumble. It is sweet sounding.

Mike

Yeah, that new rumble is definately worth the extra .20 a gallon.

[frenzy1]

I'M DRUNK

[Agriv8r]

[H2 007]

Have the same slight rough idle at times as others have mentioned. Have been using Shell 87 since day one. Just filled up today and got 13.6 MPG, city driving, with 1050 miles on it.

On the highway, if I set the cruise to 65MPH, I can get a solid 16 - 17 MPG. Driving around rural roads at 40-45MPH and I have seen 18+ MPG.

Of course this is all with very conservative driving.

No knocks, pings or anything else for that matter.

Overall, I think this new engine / trans / gearing is great.

[HUMMERcustoms.com/TAZ]

Bumping HP is just adding fuel/air then adjusting timing. If you are running what factory calls for then take it to dealer and have it checked something is wrong. It could even be the knock sensor. You may need a spark plug colder or hotter. There are so many variables to a knock it takes someone with software etc. to check it out. You could play with a handheld, experiment taking notes save allot of money and figure it out.

Tuning is note hard just requires some study up front on how the new stuff works. I use to just ear tune back in the muscle car days. I miss it. Run Accel distributor stuff etc. Figure fuel/air ratio on a printed table based on carb, heads, cam, and just figure your way. Once it was all done the final timing was done by ear at about 2000/2500 rpm by ear no timing light. I could put my 68 Mustang 289HP 3/4 race cam, roller rocker/lifters, and tunnel ram then time it perfectly on the money. Next it was pink slip time.

TAZ

[blackhawk29]

Originally Posted by H2 007

Have the same slight rough idle at times as others have mentioned. Have been using Shell 87 since day one. Just filled up today and got 13.6 MPG, city driving, with 1050 miles on it.

On the highway, if I set the cruise to 65MPH, I can get a solid 16 - 17 MPG. Driving around rural roads at 40-45MPH and I have seen 18+ MPG.

Of course this is all with very conservative driving.

No knocks, pings or anything else for that matter.

Overall, I think this new engine / trans / gearing is great.

for what it matters my 08' f-450 twin turbo idles smoother than my 08 H2. Sounds like most 08's have a rough idle. at a stop light the other day, the engine idled up by itself kinda lurched forward, if i did not have the brakes firmly on it would have ended up in the back of someones car. i think gm has something messed up with the ECM fuel mapping and they need to issue a reflash update. My idle is so rough that it almost feels like its going to stall out, i can watch a bottle of water jump all over the place in my cupholder. I can also feel it through the brake pedal. I'm all for the exhaust note and hot cam, but can't we have that with a vehicle that idles properly?

[WikidPete]

I've got almost 7,000 miles and still running great...
I do agree the engine has a bit of a rough idle.

[Tex_h2]

Originally Posted by Agriv8r

if you dont change it how do you know....

I have used reg, every now and then and noticed a lag or decrease in power

[Tex_h2]

Originally Posted by blackhawk29

for what it matters my 08' f-450 twin turbo idles smoother than my 08 H2. Sounds like most 08's have a rough idle. at a stop light the other day, the engine idled up by itself kinda lurched forward, if i did not have the brakes firmly on it would have ended up in the back of someones car. i think gm has something messed up with the ECM fuel mapping and they need to issue a reflash update. My idle is so rough that it almost feels like its going to stall out, i can watch a bottle of water jump all over the place in my cupholder. I can also feel it through the brake pedal. I'm all for the exhaust note and hot cam, but can't we have that with a vehicle that idles properly?

That sucks......I have to say my 04 pur's like a kitten

[j e f f x o 6 x]

im close to 10,000 miles on my 08 H2 and still running strong with 87 octane

[mikejr]

I've got about 4K on my 08 and she's running like a top. Yes, the idle is rougher than what it was in my 06. I've been burning regular in it since day 1. Maybe will try a load of hi test in it to see what happens.

I recall when they bumped the ponies up in the avalanche from one year to the next, the newer one had the same rough idle situation....went from an 03 to an 04.

[CovertH2]

The Diablo Predator programmer has a program for 87 octane, just ran it into my '08 two days ago, runs fine. Prior to that no issues ever running on unleaded. FYI.

[Little General]

I got 3000+ miles on my 08 and have run 93 since new. Found out the other day that the dealer puts 87 in for the free tank with purchase because of the cost. On top of that , this is the first new car I have ever bought that did not include the first oil change free. I read it is the same +/- engine as the corvette and all corvettes come with Mobil 1 from the factory, H2's come with dino. Since I had to do my first oil change at my cost, I put Mobil 1 in mine. I will report if mpg's change.