Gas Mileage Help Needed!

[Boomer34]

I have recently bought a nice '99 2500 Suburban. It only has 100K miles and is in great shape. I had all the fluids replaced when I got it and put on some new Bilstein shocks. Not much else was needed. I have been tracking my gas mpg over the first 1,000 miles I have had it. I made 1 long highway trip and got 10.9 mpg. Since then, I have done mostly city driving and have gotten 9.8, 9.4 and 8.6 mpg on my last 3 tanks. 

I am wondering what I can do to improve this. I have done a little research on here and have read about doing the cold air intake, a friend mentioned removing the catalytic converter...I'm not a "car" guy, so don't know much about "under the hood" type work...I did check, and it appears the fuel filter has been replaced recently (Car Fax says it was a couple thousand miles ago, and it's an after market one). My fuel pump does wheeze while the truck is cranked. 

I'd do pretty much anything needed to get 2-4 mpg more than I am now. This is going to be our main family car, so it will be driven a lot and we are planning to keep it for the next decade.

Thanks for any insight!

[riverbanks]

My opinion,leave the cat.,pass on the cai.,get it on a scanner and see how it's doing,02s behaving properly

[swathdiver]

Yep, scan it first to see if everything is working properly and if there are any underlying problems or codes in history.  Then do your mods.  

 

Since this is the old GMT-400, which motor, 454?  Which gears?

[Boomer34]

14 hours ago, swathdiver said:

Yep, scan it first to see if everything is working properly and if there are any underlying problems or codes in history.  Then do your mods.  

 

Since this is the old GMT-400, which motor, 454?  Which gears?

Yeah, it's the 7.4L 454. So I know it will never get great mpg, but I would love for it to creep closer to the 12ish number! Haha.

 

When I got it, my friend who has a auto shop did the scan. Everything was good with it...no error codes. I'm assuming that's what you mean...

[riverbanks]

You could do a fuel pressure test,and scan it,check the fuel trims,see where it's at,you said"good"with the check,be nice to hear the word"spot on","perfect"

[swathdiver]

31 minutes ago, Boomer34 said:

Yeah, it's the 7.4L 454. So I know it will never get great mpg, but I would love for it to creep closer to the 12ish number! Haha.

 

When I got it, my friend who has a auto shop did the scan. Everything was good with it...no error codes. I'm assuming that's what you mean...

Not just checking the codes but monitoring the engine sensors too like riverbanks mentions.  A catalytic converter on its way out can still deliver decent performance and kill your gas mileage too.

[Nashman]

Don't expect much better mileage. I've had my 7.4/454 K2500 Truck for 19 years and the mileage hasn't gotten better or worse except in the winter when the oxygenated fuel comes out then it gets 1-2 mpg worse. I figure since I haven't had a car payment for at least 15 years I can afford the gas.