brock mann

I pick up my 2000 Silverado Z71(5.3 auto) last month used with 100,000 miles on.
I have ran several tanks of gas through it and I can only get 13 mpg. It doesn't matter if I romp on it all day, run 400 miles on the freeway,or grampa it around town. I only get beteewn 13.1 & 13.7 mpg. Is this a normal thing?
I bought an Airaid filter kit(200-112-1) and pick up a borla cat back exhaust used. None of this helped. I received a throttle body spacer with the air filter but havent put it on yet.
I have a crane cam(#Hr 208 294 2S 13.55) I bought used on ebay and plan on putting it in when it gets warmer out. I also plan on putting LT headers on about the same time.
The truck is my daily driver. Right now the truck cant dig its way out of its way until you hit about 3500 rpm then hang on. I've always had hopped up s10s in the past so the 5.3 is new to me.
I only get 1 ses code and its for the purge solenoid on the gas tank. It was 100.00 from the parts store. I have to drop the tank to get to the one on this truck.
Thanks for any help on my issues.

5.3 GMC

Change the fuel filter. It's probably never been changed. Inside the frame, drivers side, between middle of door and tank.

chevymec

iTrader: (19)

Purge valve is on the intake, vent valve is on the tank and you dont have to drop it to replace. I cant get over 13 mpg in my 2000 Z71 so I feel your pain.

TX Tahoe Z71

iTrader: (28)

Change the spark plugs, TR55 gapped at .055". Clean the MAF sensor with the spray you can get at any auto parts store. Fuel filter is a great idea too. Seafoam top end treatment (good write up on LS1tech). If none of that helps, replace the FRONT O2 sensors (even if you aren't getting a code thrown) with AC Delcos or Delphis (forgot which are the good ones, but don't get Chinese or Bosch), check RockAuto.com.

But the biggest difference maker is a tune! Check sponsors on the right, Wheatley, Nelson and Blackbear are all great tuners.

EDIT: Oh, sell the throttle body spacer to help pay for this, that is only good as a paper weight.

brock mann

To all.
The fuel filter was changed last year with the fuel pump.
TX Tahoe Z71 I'll look for seafoam. I've used it on carb cars but never FI cars. I will also try cleaning thethe MAF.
Dumb question what brand plug? AC Delco?
chevymec I look on truck in the yard and it was on the middle of the frame, but mine isnt. I am guessing that it is located on or close to the frame. Really 13mpg even on the highway? The previous owner said he'd get 22 mpg on the highway. My buddy with a Sierra gets around 24 highway. Hes odd though. He get 100,000 miles out of 80,000 miles tires too. Yes I saw it with my own eyes.lol
Thanks everyone!

chevymec

iTrader: (19)

Look behind the drivers side of the cab at the front of the tank. It is a tight fit. I usually always cut the tube off them and with some force yank it out of the holders.

TX Tahoe Z71

iTrader: (28)

Typically, you will see 16-18mpg on the highway in a tuned up Z71 ecsb (extended cab, short bed). I highly doubt your friends were seeing 20 or 22mpg on average unless they were running no A/C on a perfectly level road at 65mph the entire way AND had an aftermarket tune.

Spark plug brand is NGK, TR55 is the plug. Typically want to change them every 20-25k miles to keep it running well.

brock mann

I havent installed the cam or headers yet. I'm waiting for the weather in Ohio to warm up. The only mods I've done so far are the air cleaner and Borla exhaust.

oldred95

My 99 got 16-17 all stock on the highway 65-70 mph. If I ran 75-80 on the turn pike it would drop off to about 15-16 mpg. On the last road trip to Dallas running 75 mph through the rolling hills on I35 it managed to get 16.5 mpg. Its taller and wider with bigger tires but it does better mostly due to the fans. My fan clutch seemed to be mostly engaged all the time. The efans really freed it up. I would imagine I could get 18ish if I kept it at 65 and drove nicely. FWIW my daily commute is 24 miles and it gets a consistent 14-15 mpg running 70 mph.

CalEditor@PCMCalibrators

iTrader: (4)

+1
Just get a tune and check the O2's