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2003 GMC 2500HD 8.1L

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Matt Weltz

11-27-2007 14:49:13

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Hey guys! Dad has an '03 GMC 2500HD extended cab, long box, 4x4. Has the 8.1L V8 and allison 5-speed. Truck has just over 10,000 miles and is only used for pulling. Now we can;t complain because it doesn't get used that often and it does its job well but we are looking to improve its gas mileage. Truck is all stock with the exception of a K&N Gen. II mass air-intake kit. What would you recommend; programmer, performance chip...? What are the pros and cons of each. Am up for any ideas short of trading for a diesel! Thank you!!!

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Retento

11-28-2007 04:28:09

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Re: 2003 GMC 2500HD 8.1L in reply to Matt Weltz, 11-27-2007 14:49:13

Put the stock air cleaner back on and leave it alone. It's a 496 cid gas engine, it's going to burn alot of fuel. No chip, magic filter or exhaust is going to help. Gale Banks don't even make an aftermarket exhaust syatem for the pickups, they said there was nothing they could do to make it any better than what was installed at the factory. Gas it up and enjoy! Retento, proud owner of a 2001 8.1/Allison 3500 ext. cab 4x4!

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Lenny Kirby

11-27-2007 17:56:26

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Re: 2003 GMC 2500HD 8.1L in reply to Matt Weltz, 11-27-2007 14:49:13

I have an '03 GMC 2500HD ext cab short bed. 8.1L 5spd allison. I hyperteched mine and have had no problems I don't know what it would get before because I already had the programmer and did it the day I bought it. I pull a 25x5 triple axle 21k trailer and with light load of 5500lbs pulling tractor I will get about 7-8 mpg depending on wind. empty with no trailer i'll get 14+ between 60-65 mph won't average that but that is what the instant computer says when I drive... 50,000 miles 3.73 rear end..

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bradk

11-27-2007 17:21:42

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Re: 2003 GMC 2500HD 8.1L in reply to Matt Weltz, 11-27-2007 14:49:13

Not too fond of the K&N systems either.Yes the oil gets on MAF sensors and gives drivability issues.

Best thing you could do on the truck is to properly inflate tires and use a premium synthetic lube in engine,t-case and diff's. ~brad

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Tom43

11-27-2007 17:19:33

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Re: 2003 GMC 2500HD 8.1L in reply to Matt Weltz, 11-27-2007 14:49:13

LEAVE IT ALONE!
General Motors paid their engineers a lot of money to optimize the balance between power, fuel economy, and emission laws. Why do you think the aftermarket snake oil salesmen would know so much more than the company engineers? All codes and sensor readings can be read on a scan tool since 1981 on G.M. vehicles.

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RustyFarmall

11-27-2007 17:12:58

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Re: 2003 GMC 2500HD 8.1L in reply to Matt Weltz, 11-27-2007 14:49:13

I would never waste my money on that K&N system. I've been told that the oil you put on that filter will get on the MAF sensor and mess up the whole system. I have a 2001 K3500 with the 8.1 and 6 speed manual. I modified the air box to allow more air flow, kept the stock filter, removed the plastic mesh screen from the MAF, and gained at least 2 miles per gallon. The mods didn't cost me a dime.

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Ken in MN

11-27-2007 16:38:42

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Re: 2003 GMC 2500HD 8.1L in reply to Matt Weltz, 11-27-2007 14:49:13

I have an 03 2500HD with the 8.1, allison, ext cab shortbed 4X4. The best I can get for mileage around here in north central MN is high 10's. Last july The wife and I went to southern MO on vacation, down there I was getting around 13.8 mpg, with a best of 14.9. As we were driving home, the closer we got to home , the worse the mileage got. Still have not figured that one out. My truck will do slightly better with 89 octane versus 87. I have never used a programmer, but have heard that hypertech is not a very good one for these engines. Check out dieselplace.com, there is a section for "gassers" that has some useful info.

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RusselAZ

11-27-2007 16:12:22

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Re: 2003 GMC 2500HD 8.1L in reply to Matt Weltz, 11-27-2007 14:49:13

Pulling what?

I'd leave it alone and for sure keep that KN clean and oiled. And, there is no gain of getting more air in the engine if you didn't do anything to get it out. There are some nice exhaust systems out there.

All that performance chip junk out there is for people who like to show off on main street, not for heavy long hauls.

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Matt Weltz

11-27-2007 17:28:36

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Re: 2003 GMC 2500HD 8.1L in reply to RusselAZ, 11-27-2007 16:12:22

Hay and farm equipment on 20,000GVWR gooseneck fully loaded majority of the time. Can get 10-11MPG empty if I'm lucky and anywhere from 4-5MPG loaded. Have K&N on all my vehicles with no problems. Will check into performance exhaust systems. What do you guys think of the throttle body spacers???

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IaGary

11-27-2007 15:09:13

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Re: 2003 GMC 2500HD 8.1L in reply to Matt Weltz, 11-27-2007 14:49:13

With only putting 2000 miles a year on it, anything you spend much money for to save fuel will not pay.

You are spending $600 or less a year for gas.

If you increase the mileage by 10% that is only going to save you $60 a year.

Can"t buy many parts with that.

Switching to a diesel will cost at least $6000 more than a gas truck.

The interest on that $6000 will be $480 a year.

Do you think you will save $480 a year burning diesel instead of gas at the rate you put on miles.

Diesel trucks only pay for the guys that put on over 20,000 a year and keep them for several years.

The rest is prestige.

Just my view.

Gary

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Matt Weltz

11-27-2007 15:45:58

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Re: 2003 GMC 2500HD 8.1L in reply to IaGary, 11-27-2007 15:09:13

Spending closer $1200 a year on gas. So if I could get a 10% increase and save $120 bucks a year by spending a couple hundred right now, then I am all for it. I like the programmers because you can fine tune things to your individual needs and check enigne codes/sensors and things but have never had any experience with them and was wondering if any one is better than any other. Anybody had any experience with them???

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I don't have a name

11-27-2007 19:48:24

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Re: 2003 GMC 2500HD 8.1L in reply to Matt Weltz, 11-27-2007 15:45:58

Aftermarket parts are expensive, and I really doubt you could improve the fuel economy of that big block much, if any and you might make it worse. I'd suggest swapping the truck for a Dodge Hemi with MDS or something, however you'd be sure to lose more money on the deal than you would if you just left it alone, and just bought the gas for what little you do. Heavy hauling is NEVER going to be cheap.

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buickanddeere

11-27-2007 15:27:49

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Re: 2003 GMC 2500HD 8.1L in reply to IaGary, 11-27-2007 15:09:13

I agree. That K&N aircleaner is great for the race track but not so great for the street. The K&N only strains out the bigger lumps of dirt. Go back to a quality paper filter built by Whix, certainly not a Fram. A premium quality programmer isn't going to hurt and it allow a few extra HP if you run 91 octane. You can also adjust the shift point rpms & ground speed. This can get away from hunting up and down with gear shift on small hills were a geared down and revved up engine isn't required. With a good programmer you can tweak the air/fuel mixture a little leaner for economy as well. The programmer will let you read codes, re-set codes and check various engine functions and sensor conditions.

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