06 Sierra Owner... Ignorant And Need Help!

AD_ NAPCO · November 20, 2009

Howdy guys,

I can tell ya all kinds of fun facts regarding 1939-1959 Chevy and GMC trucks, but my knowledge and awareness of anything in this century is extremely limited.

I ordered my 2006 GMC Sierra Crew Cab 4x4 with 5.3 (supposedly my only option at the time) and 3.73 rear end, and took delivery in 12/05. The truck has been great, and worked probably harder than it was designed to, towing pretty darned heavy loads like a champ... It has about 85K on the odometer at this point. Hasn't suffered any performance losses, that I can really tell, but the mileage has gone downhill. When it was new, it got an average of 18.5 mpg with mixed driving, mostly freeway, and I don't have a heavy foot... Usually keep it between 65-70 cruising around 2K RPM's, maybe 2200 on average. Lately, I can't seem to keep it much higher than about 15 mpg. Now, granted... I haven't tuned the truck up at all. I know... That is probably real bad. It seems to run exactly the same as it did the day I bought it, so I hadn't seen the need.

The only things about the truck that are non stock, and did immediately affect the gas mileage noticeably when I did them, was that I installed a front end levelling kit to get a little better clearance for the front valance when I'm off road, and some stock size, yet slightly more aggressive mud/snow BF Goodrich tires.

I guess, what I'm looking for is advice on what kind of upgrades can be made that will bring both performance and fuel economy back up. I would assume that just a tuneup would help, and maybe cleaning the fuel injection system? I bought a Haynes manual, and it really doesn't give much useful information on tuneups.

Anyone have good experience with improved tuneup parts like plugs, wires, and the like that have been maybe more expensive than stock, but noticeably worth the upgrade? What about cold air intakes? I'm almost thinking I've read that my truck is cold air from the factory... Is that true? What about recommendations for cleaning the fuel system out? Cat-back systems that have produced good results?

Thanks in advance for any help. It is most appreciated!

SeirraRR · November 20, 2009

Welcome to the site. The leveling kit will affect the mileage a little. I know when I did mine it did.You might want to look at a Black Bear tune for your truck. I have read on here that one of these tunes does wonders.

jjohns · November 20, 2009

Welcome. You will get more for your money if you do the tune up. New plugs and wires will do wonders. Some have reported good results from a performance tune. If you read through the posts on the subject, you will find varying opinions on whether cold air intakes or cat back exhausts are worth the money if you are looking for a mileage increase. They can make your truck sound better. Good luck.

cerbomark · November 20, 2009

He makes good sense. Welcome.

99silveradoz71 · November 20, 2009

Welcome aboard

04silverado1500 · November 20, 2009

Check your air filter, plugs, wires, o2 sensors, also make sure your tires are properly inflated and have the proper tread. After that, sea foam works pretty well if need be. It helps with cleaning. You may want to take a look at the egr valve? My friends truck got just crap mileage when his egr valve was clogged up. (though if your egr valve is bad enough you should notice a rough idle) the last thing you may want to look into is a tune as mentioned above. have you gotten gas from anywhere out of the norm lately? I would venture to guess if you have 3.73 gears your rpms run at or just shy of 2k at 65-70. I had 3.73s in my 04 silverado 5.3 and it ran 2,300 (roughly) @ 80 mph and 2000 at 70 if i remember right... if not those rpms you would likely have something closer to 4.10s. All of that info should be in your glove box ex. code G80 locking differential (i believe). Hope this helps!

AD_ NAPCO · November 20, 2009

Check your air filter, plugs, wires, o2 sensors, also make sure your tires are properly inflated and have the proper tread. After that, sea foam works pretty well if need be. It helps with cleaning. You may want to take a look at the egr valve? My friends truck got just crap mileage when his egr valve was clogged up. (though if your egr valve is bad enough you should notice a rough idle) the last thing you may want to look into is a tune as mentioned above. have you gotten gas from anywhere out of the norm lately? I would venture to guess if you have 3.73 gears your rpms run at or just shy of 2k at 65-70. I had 3.73s in my 04 silverado 5.3 and it ran 2,300 (roughly) @ 80 mph and 2000 at 70 if i remember right... if not those rpms you would likely have something closer to 4.10s. All of that info should be in your glove box ex. code G80 locking differential (i believe). Hope this helps!

Thanks for the welcome, guys.

04silverado1500, you are correct about the RPM's. I do have a posi 3.73 diff. I ordered the truck that way from the factory. I am going to take everyone's suggestion and just do some basics up front. Plugs and wires, double check my air filter (just had it serviced, but it never hurts to look again) and look into a good additive to run through the fuel system and see how things go. Like I said though... The truck runs great! It's just been dropping the gas mileage pretty steadily over the past six months or so.

Thanks a lot for the help!! I will report back how things go!

MADS99 · November 20, 2009

Welcome to the Site Josh...

pwall · November 20, 2009

Welcome!

MS3DALE · November 21, 2009

Welcome!!

AD_ NAPCO · November 21, 2009

Welcome!!

Well, I filled up the tank yesterday and added a can of Sea Foam as recommended, after buying new plugs and wires at NAPA. Changed out the plugs and wires about an hour ago and took the truck on about a 30 mile mixed driving shakedown run. Looks like I managed to get back about 3 mpg, and some power I didn't realize I'd lost at the top end... So that's great! I think next time I buy tires I'm going to tone down the tread a bit, as I'm not getting offroad nearly as much as I used to. Probably get back at least 1 mpg doing that, and definitely better tire life!

thanks for the help guys!

Josh

MS3DALE · November 21, 2009

Hey....How 'bout posting some pics and specs of the NAPCO 4x4's?

wpgmachoman · November 22, 2009

Check your air filter, plugs, wires, o2 sensors, also make sure your tires are properly inflated and have the proper tread. After that, sea foam works pretty well if need be. It helps with cleaning. You may want to take a look at the egr valve? My friends truck got just crap mileage when his egr valve was clogged up. (though if your egr valve is bad enough you should notice a rough idle) .....

The tune up; wires and plugs will do wonders. I borrowed by Dads '97 1500 Silverado (5.7) last year for a trip with his camper. The whole trip, it seemed to suck and the milage, while,,,no comment.

I kept the rig at my place for a few weeks afterwards,,,and since he let me borrow it..I did the whole tune up thing for him. I am telling you...it was like a new truck. I even changed the coolant for him, new oil, plugs wires, egr, cleaned the TBI. Dad never really does that stuff, he barely drives it. But before we gave the rig back,...took the camper out to the local lake. I swear it pulled fantastic, and got significanly more milage (still sucked of course,,but better than before). The only thing I didn't do was change the trans oil...told him he should. Hate that 4 speed trans though...main reason when i bought my truck, the six speed alli is excellent!