My son recently purchased a 2001 suburban 1500 LT w/the 5.3L motor. It has about 115K miles on it. Upon first couple fill-ups, it was getting close to 20 MPG.
He decided to change the spark plugs and wires just as preventative thing.
He used AC/Delco Iridium plugs gapped at 0.40 and same as OEM plug wires. Air filter as well as oil and filter changed too.
Now it seems that the burb is only getting a bit over 10 MPG and we are not sure why. It runs great, does not stumble or rough idle; basically smooth as ever. Power is a bit better actually but now suffers a big loss in gas milage.
Thoughts anyone? Should it go to the dealer/stealer and put on an analyzer? Would that show up any problems in how and why the vehicle is getting bad gas milage? Anything WE can do to check for problems? Thanks all!
This one's for you MKR!

 

Quit stealing my posts!

- mike

 

Just a thought but the tune up may have come with heavier foot.
You can't have both pick one "Power is a bit better actually but now suffers a big loss in gas mileage"

Have him go easy on the accelerator for a few fill ups and the MPG will most likely return....

 

Same thing happens when you put in a CAI and/or louder muffler. Must be a guy thing.

 

Um, my son's wife actually drives it the most. And he will agree, he doesn't have a "lead" foot; he knows better due to gas prices/milage issues.
Can we get a bit more technical? He's already after me b/c I stole his post before he had the chance. Guess I jumped the gun a bit.

Seriously, something has to be wrong to lose that many MPG right after changing those plugs, wires, filter etc.

 

well, my 01 with 33's and 18's and 150k is getting 13average, (5.3 too) highest I've gotten was off this last tank in the 15.5 area. this is without the much needed oil change/plugs/plug wires I feel it needs since I just recently got it, (funds extremely tight right now) plus I'm lending credit to the fact it's new and I'm still a bit heavy with my foot.

all that said...

I can't think of any reason why the changes that have been made would drop the mpg... provided the plugs are gapped correctly and all and even then I think you'd notice a stumble or something...

anyhow how many tanks has it been thru since the maint work?

:chug:

 

I'd start by checking all of the wiring and hoses around and near anything that was replaced or worked on. I suspect a loose, cracked, or disconnected vacuum hose.

 

I can't see how a competent tune up would affect MPG adversely...
The gas blend hasn't changed to to a winter blend that contains more ethanol?
more alcohol = lower mpg but usually lower power and you said power was up.
verify that the idle rpm is within range
check that nothing else has changed with tires, towing, alignment...

 

too much junk in da trunk?

 

I've always found if the truck or car is stock engine wise just use the recomended plugs and wires. Sometimes upgrading them makes things worse.