Poor MPG for 5.3L Silverado

[jrucsky]

Hello, I have a 2000 Silverado 1500, 3.73's, 285/75/16 AT's, K&N intake & duel Flowmasters exh. The truck has a 4" Rancho susp lift that sits at about 2.5", and has rear leaf's from a 2500. Currently apprx 118k miles on it. I love the truck and trust it enough to go anywhere in it.

 

When I 1st bought the truck I was getting around19-20hwy. Lifting it cost me 1-2mpg's, so I was getting 17-18hwy. At about 50k the MPG's dropped dramatically. I started getting at best 15mpg no matter how easy I took it. I had everything I could think of looked at. I had two Carbon flushes done to it by the dealer, changed plugs, Flitters, tranny serviced, rake added to the front, pumped tires to max. I've really tried everything I could think of. No one has been able to give me any direction on how to recover any mpg's. I use the truck for work daily, I do a lot of driving, and as of the last 30k miles I've been getting no better than 12mpg's on my mixed use tanks. On the tank I'm on currently, its looking like I'm heading for about 10mpg's, And I've had enough!!! I love the truck but there is no reason a light use of a 1/2 ton should be getting big block type mpg's. Can anyone please help!!!!? I was told of a kit called something like a spyder injector kit, that swaps out the injectors. When I search I find stuff for the old 5.7's and 4.3's but nothing on the 5.3L. I don't expect to get great Mpg's out of a truck driven in around the city, but 10-12 is rediculous! I don't want to sell the truck but .55/mile doesn't ease the pain of 10mpg's. I mean if that's all the better I'm gonna expect I should at least go get a 2500 or 3500 with a big block, cause then I can actually work the truck. Please Please Help!

 

 

Thank You

[markw8]

With everything you've done with the truck, that's probably all your going to get. Are you hauling tools or material every day?

 

Mark

[00Silverado4x4]

Cleaned your MAF sensor.

Fuel injection cleaner.

Personally wouldn't run tires at max, but not sure if that would hurt your mpg

What are your engine running temps, if it's running colder than norm your computer could be dumping fuel unnecessarily.

When's the last time you've changed fluids in axles.

Checked to make sure you don't have a brake hanging up.

 

A few ideas off the top of my head.

[Jsdirt]

Don't know what part of North America you live ... but in the state of MA they load the fuel up with ethanol. It's posted at the pump as 10% ... but in reality it's double that ... and to top it all off, it varies from station to station ... and even the same station! Enough to make you crazy .. but nobody reports on it or even mentions it - heck I'll bet 99.9% of drivers don't have a clue! But I'll tell you this - if you get a batch of fuel with 20% ethanol in it, it will knock a minimum of 5 mpg off compared to a station selling true 10% or less. Noticeable seat-of-the-pants loss of power as well.

 

Just one more factor to throw in, depending on your location.

[GMstrong]

I agree on the injector cleaner,Also how long ago did you do plugs and wires?Clean the MAF,Thorttle body out too.

[gm4yrs]

I would change the upstream o2 sensors. The sensors do affect fuel mileage.

[jrucsky]

I don't haul anything that weighs much, mostly just me. I'll check those suggestions. Are those items things that I should have a professional do? I'm not a very good Mechanic. Thanks for any and all suggestions

[redjewel2ss]

i agree with the other guys,

 

check your engine temps, do you have an after market thermostat? if so, is the ECU re-programmed for it?

inspect your O2 sensors and cats. if one or both of those are bad = bad mileage as well

 

i wouldn't put the max psi in the tires, only in the rears if your hauling a load. i used to work at a tire shop and we would tell people with larger than factory tires to put 10-15 psi less air than the max, as long as that didn't go below the factory specs. on E rated tires we set them to 50 psi. on C and D rated tires, we usually put 40 psi unless the max was less than that.

 

don't expect better than 15mpg highway with a lift, taller tires, and 3.73 gears with that 4 speed

[Sarampion]

Hi

When a poor mileage is an issue we always check:

1)Air Filter

2)MAF/IAT Sensor

3)Throttle Body

4)O2 Sensor Upstream

5)ECT Sensor

6)Spark Plugs

7)Wires

8)Small Gas leaking in lines, injectors, fuel pressure regulator, tank, ect., even if has not been set a trouble code

9)Tires (Pressure, Alignment)

 

Take special atention to O2 sensors and ECT sensor, even if they look good and dont set a trouble code.

Maybe they dont sent the correct amount of voltage to the PCM and therefore the computer is runing in a rich fuel mixture

 

Good Luck

[waumo1]

I would change the upstream o2 sensors. The sensors do affect fuel mileage.

 

Agree - they can start to degrade by 50K miles

[jesben9597]

I have several ideas for you. This is what ended up fixing my truck. I bought the actron scan tool off ebay. Its actually made by otc. works good. My son and i were on a lond drive one sunday. We were looking at the input sensors to the pcm. The engine coolent temp was beteeen 240 and 278. wow. I stop at a hardware store bought a thermometor they use to put in turkeys when there being cooked. put it in the radiator it read 195. I was scratching on head because i had already replace the ect sensor. So how could this be. after some research there are two ect sensors one for the temp gauge witch is thye one i replaced, and one for the pcm. I replace the other ect sensor. unhooked the battery for the night. the next tank i went up. 2.8 mile per gallon. Bingo I got it fixed.

One thing you said in your description is tire size. That size doesent look like the stock size to me. If you changed it, did you have the speedometer recalibrated. if you dident your not gettng the real mpg in your figureing. The odometer would rear 1 mile when you actually traveled 1.1 as an example.

 

Hope this helps.

[Mike of the North]

All I have ever gotten for the life of my 2010 4.8l extended cab stock silverado is 11 miles per gallon in the city. Seems pretty standard to me.

[Conky Conky]

11 I wish I'm at 9mpg city with my5.3 and 12-14 MPG on freeway I have 5.3 with 6spd 2.5 inch lift at all fours and 32s. I got 16MPG once but that was one of them perfect days with I think a bit of tail wind. It's funny how GM made a full-size truck for years that could get 30mpg now a days its hard to find a full-size that gets 20mpg my nabours 89 Chevy 1500 2wd has 6.2 diesel and its around 31mpg with almost 600 000km.

[swathdiver]

Wonder if the OP still has his truck?  Anyhow, sensor degradation, vacuum leaks and aging catalytic converters all contribute to reduced fuel efficiency.  A good scan tool that allows one to see what the computer sees is essential to keep these engines in top form.