2003 H2, 1 year ago completed a project of returning the engine to stock configuration. Previous owner had an airaid cold air intake, aftermarket injectors, mismatched aftermarket O2 sensors and some sort of tune in the ECM. Mileage was about 11.2 MPG overall average. 112,000 miles at the time. Currently at 120,000 miles after replacing all gaskets and seals, new oil pump and timing set, went through the cylinder heads, new LS7 Delphi lifters with Brian tooley racing pushrods and trunnion kit. Replaced all sensors with ACDelco genuine GM, replaced ECM with a new one which supersedes the original, updated OEM programming. Factory air box and filter, updated valve covers with the orifice instead of the PCV valve.

I live in a rural area, nearest town is 25 miles away on State highway. Minimal city driving.

Overall average fuel economy at the one-year mark, 13.6 MPG calculated on paper. I'm not concerned with fuel mileage, I just pay attention to it as I measure of how efficient the engine is running and therefore the condition. Around town it gets in the low 12s, long drives at 65 on a road trip I've seen 14.2 on a tank.

Only failure was one genuine GM knock sensor about 4000 miles old. Other than that it's been extremely reliable. I've done a lot of other things as well, new body control module, had the cluster rebuilt with new stepper motors, new you joints, the entire cooling system as well as all AC components under the hood. Stainless steel cat back exhaust. (NOS Obx system I got dirt cheap, date of manufacture on the box was 2005!) Pistons and rings are all original, absolutely zero leaks and doesn't use any oil between changes.

Very, very pleased with the vehicle. No rust, and the paint is almost in new condition.

Can't say for sure why it was getting such poor fuel mileage when I bought it. Probably a combination of that cold air intake, incorrect tuning, a no name mass air flow sensor and a host of other oddities.

 

I have a friend who goes by the "Stock is best" moto, he was referring to Harley's, but there is a lot of truth to that statement. My H2 is all stock with the exception of a Borla cat back and a somewhat rare Rockford Fosgate H2 subwoofer kit.

Sounds like you found a winning combination.

 

I figured I'd get it back to stock at least as a baseline.... Then consider whatever options after that. But it does just fine in stock trim, even pulling my 12 ft dump trailer and the boat every now and then. The funny thing is my wife says it rides better than her 2014 Escalade and actually feels somewhat safer. Probably has a lot to do with the weight. A lighter vehicle with low profile tires like the Escalade, you feel the little bumps more.

 

Yep I'm the same way. GM did a lot of trial and error stuff on that chassis and motor and driveline. My 2009 H2...6.2 motor at 55 MPH on a long run can squeak out about 18 MPG. That's on 93 Octane Gulf Tier 1 fuel. City runs about 12. Never burns any oil. Average mileage per year is about 7K. The clock shows about 71K miles.

I change oil (Mobil One 5W30 every 6 months. I never go by the ...you can get 5000 miles between oil change thing. It's always run Mobil One. It just the leak in at the A pillar and Passenger side mirror that bugs me.

 

The leak in the a-pillar.... If not the grommet under that corner marker light, it's the forward most screw holding the roof rack down. Thread sealant does wonders.

At 55 mph driving like my grandmother used to, I can get in the low 16s. LOL, even at my age I don't have the patience for that though.

 

Thanks Robert... We covered this in another thread,,,, I did the roof rail bolt...the sucker is still getting wet over the A pillar headliner. The meck-en -ic once told me years ago that it could be a pinch weld between the top and the underside of the sheet metal. But that means taking out the headliner.

Next year I think I am just going to take it in to there body shop and have them rip out the headliner and flow water down that roof channel and find that leak . Then just spring for a Brand new Headliner. I'm guessing about 5 G's worth of work. What me worry....Fatboy is my Baby.

And I don't drive 55.!! at 70 MPH I'll get about 14 MPH in 6th gear with the old 6L80E.

 

are you running 4.56 gears? My truck on 37s with 3.73s won’t maintain 70 in 6th. It was actually so bad that I tuned 6th out and run 5th which is almost equivalent to 4.56 gears. Mpg went up from 9.5-13ish

 

Nope ...I have no clue what *** end ratio is in there. But it is stock to and Air Ride and 6L80E as a 2009 Lux. The tire size call out on the "B" pillar placards is not made any more. What I mean is the total circumference of the tire is 1/4" larger on the new tires I have. There made buy Firestone and they are all terrain and run quiet on the street. Not like my old Off Road Super Swampers that hummed along with the radio and drove me nuts everytime I put them on to go off roading.

So all in all you might as well say there a Stock Factory Tire Size.

 

I do wish GM would have kept the pre 08/09 MY 4.11 ratios, with the 6l80 and new 6.2 I think the H2 would have squeak out a bit more fuel economy as well as a bit more performance.

If there was anything I would do with mine would be go to 4.11 ratio's with the 35" tires I am currently running. If I ever jumped to 37's I would spring for 4.56.

 

i belive the 03-07 have 4.10 not 4.11 gearing.