2009 Sierra 5.3. Horrible Fuel Economy. Help!

[Parsonsjb88]

I just purchased a 2009 Sierra Extended Cab 4x4, z71, 3.73 rear, 5.3L AFM, 4 speed. The truck is like brand new, only 37,000km. No other issues other than getting 7-8 mpg towing a car hwy and about 13 mpg highway unloaded. My last highway trip I did (like a 400lb load in the box), I barely managed to break 500km to a 100L tank and that was at 105km/h and cruise control as much as possible with very little passing. This is boggling my mind considering my brother has an 08 4.8 4 speed and he is getting 18mpg highway. All these results are hand calculated using U.S gallons. I just purchased the truck so I am going to check a few more things today; in the midst of the excitement of purchasing the truck I didn't check the plugs or air filter so I will check those today and report back tomorrow but I am wondering if any of you guys have experienced similar disappointing fuel economy results and how you may have solved them. Any help would be greatly appreciated guys! I'm kinda freaking out cause I was expecting to get like 18mpg at least and this thing is breaking the bank already.

[maxco]

Wow. Thats surprisingly poor fuel economy. I can see 8mpg towing a trailer depending on how heavy it is, but I had an '08 Sierra set up like yours and I could do about 700 km on a tank on the hwy empty...and over 600 for sure with a boat in the bed full of camping stuff & a canoe on the roof. I think I was around 11-12 mpg with all the junk loaded...

 

Definitely check your plugs & air filter because something isn't right there.

Are your tires inflated properly? Is it out of alignment?

[Parsonsjb88]

Wow. Thats surprisingly poor fuel economy. I can see 8mpg towing a trailer depending on how heavy it is, but I had an '08 Sierra set up like yours and I could do about 700 km on a tank on the hwy empty...and over 600 for sure with a boat in the bed full of camping stuff & a canoe on the roof. I think I was around 11-12 mpg with all the junk loaded...

 

Definitely check your plugs & air filter because something isn't right there.

Are your tires inflated properly? Is it out of alignment?

 

 

The truck recently had an alignment before I purchased it, I have the service paper from the dealer they had it done at, and it drives straight as an arrow and no signs of abnormal wear on the tires. The person I purchased the truck from said he had just set the tires to the pressure on the door so I never bothered to check. They don't appear to be low but I will check that as well when I check the plugs and filter today. Thanks for the tip.

[Parsonsjb88]

So I checked the tires yesterday, pressure was at 45psi all around which is what is recommended on the door jamb. Checked the air filter and low and behold I had half a field of corn husks and hay in there (truck was purchased from a guy who lived out in the country near the corn fields) lol. I cleaned out all the stuff including some cracked up egg shells and feathers and and knocked out most of the dust and hay from the filter and replaced it. Also decided to change the spark plugs; I know they don't recommend changing them till like 70,000 according to the maintenance schedule but after getting as bad fuel economy as I was I want to try to regain some losses. I threw in some E3 plugs after some research and I can already notice a difference in not just performance but fuel economy as well. I could actually watch my gas gauge move before, now not so much I'll let you know what the improvements have been after I run a tank or so through it. Thanks for the tips Maxco.

[music]

I think you meant "35 psi"? Yup, corn and grass would kill mpg Reminds me of the time a mouse decided to build his nest in my air intake using dry dog food from the *other* side of the house... but that's another story. I emptied ~ 1 lb of food out, all the way to the air filter (89 Honda Accord).

[old-chevy-dude]

So I checked the tires yesterday, pressure was at 45psi all around which is what is recommended on the door jamb. Checked the air filter and low and behold I had half a field of corn husks and hay in there (truck was purchased from a guy who lived out in the country near the corn fields) lol. I cleaned out all the stuff including some cracked up egg shells and feathers and and knocked out most of the dust and hay from the filter and replaced it. Also decided to change the spark plugs; I know they don't recommend changing them till like 70,000 according to the maintenance schedule but after getting as bad fuel economy as I was I want to try to regain some losses. I threw in some E3 plugs after some research and I can already notice a difference in not just performance but fuel economy as well. I could actually watch my gas gauge move before, now not so much I'll let you know what the improvements have been after I run a tank or so through it. Thanks for the tips Maxco.

 

 

 

that's some funny stuff right there.. but FYI 35 psi cold is what your tires need to be set at (cold meaning they have been sitting for several hours not being driven, and have reached ambient outside temps).

 

45psi is too high and will cause excessive trie wear.

[Carder09]

Uh, I can't believe you wasted money on those e3 plugs that don't benefits your engine, you should put what came factory since that's what is going to make your truck run most efficient, and I'm sure those new mpgs aren't from those e3s but you cleaning the junk outta the filter box.

[airbalancer]

just got 2011 extend cab 5'.3 with 3.08

with about 3000km avg is 15.8l/100km

I do have a cab on and the truck weight is around 3000kg

[rgv]

stock size tires and ride height?

[Parsonsjb88]

rgv - They are slightly more aggressive all-terrain tires but same rolling diameter and the ride height is unchanged.

 

Carder09 - I purchased the E3 plugs because Canadian Tire had a huge sale on them, I paid $40 for 8 plugs so I thought it was worth a try. Considering the recent 100's of reviews I've read on them, I expect they will either help my fuel economy or it will stay the same. The funny thing is they wanted almost $50 for the stock plugs. And I agree, most of the added fuel economy will be from cleaning the filter and air box.

 

music, old-chevy-dude - As to the tires, it says 45 psi on my door jamb so thats what I put them at; either I read it wrong or that supposed to be when the tires are warm? Either way I'll check again and possibly set them to 35psi. Thanks for the tips guys!

[Superperv23]

I purchased the E3 plugs because Canadian Tire had a huge sale on them

 

There is usually a reason for a sale on something. If you still find the engine runs like crap you should check them, I have seen set of them cracking the porcelain almost immediately.

[ChevyTech77]

Heavier tires will greatly effect mpg as well.

[Parsonsjb88]

I purchased the E3 plugs because Canadian Tire had a huge sale on them

 

There is usually a reason for a sale on something. If you still find the engine runs like crap you should check them, I have seen set of them cracking the porcelain almost immediately.

 

 

They have a 5 year warranty and I kept the receipts and packaging so last chance I'll just get them replaced for free.

 

Still running a tank of gas through the truck right now, will report back will mileage when its done. Also just found out that I read the tire size wrong, sorry to those who mentioned it and I said the tire size was stock lol, I knew they were a little more aggressive than stock tires but apparently the stock tire is a 245/70 R17, and these are 285/70 R17. So firstly my odometer and speedometer are recording less speed and distance than I am actually travelling and obviously these tires are heavier and wider than stock. So this will probably make a little difference in the mpg. I am going to correct the distance travelled by calculating the difference in tire diameter and find actual miles travelled and hand calculate the mpg.

 

I did a little research on tire size changes and I "shouldn't" expect the fuel economy to drop more than 1mpg, due to this increase in size of tire. But correct me if I am wrong, this is what I read on other forums and websites and we all know its not easy to sift through the bull***t to get the truth. Thanks again guys

[redjewel2ss]

those E3's might have good reviews for other cars, but did you read any geared toward GMT-900 trucks? the stock AC Delco plugs are iridium; the highest quality you can buy. check out these reviews on E3's:

 

http://www.gmtruckclub.com/forum/f17773/ac...rk-plugs-55384/

http://www.gm-trucks.com/forums/index.php?showtopic=126713

http://www.fullsizechevy.com/forum/general...g-problems.html

http://www.performancetrucks.net/forums/gm...k-plugs-470835/

http://www.performancetrucks.net/forums/gm...k-plugs-466857/

 

a lot of people have had problems with them misfiring, or breaking after a short time. fuel mileage claims from these are mainly from people with worn out plugs to begin with. the AC Delco's will last 100,000 miles. if your truck doesn't have that many miles, put the originals back in and get a refund IMHO

[uh6tdrvr]

I have never had good luck in the 5.3 on anything other than AC Delco's. all the others started well but started misfiring and actually got worse mileage than the plugs that had 100k on them, traded for some delco's and bam, instant improvement. From what i have seen, all the hyped up plugs seem to work better on foreign engines