Bad gas mileage 9-10mpg

[TomCoppola]

Hey guys,
I dont know why im getting such bad gas mileage i drive a 1998 ECSB 5.7 i have 150,000 mi on the clock and running 265/75r16

Recently I've done:
Oil change
Plugs
Cap & rotor
Starter
New injectors
Cleaned top intake manifold

Is it just because its winter? By the way i do basically only city driving, could that just be it?



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[1997k1500Calvin]

Change fuel filter..did you change the fuel injection to the new mpfi conversion?

Tapatapatalk

 

[IOWNJUNK]

I have same truck, same motor, same mileage (149k), with 9" lift and 315's. Thats the same mileage I get while pulling an enclosed trailer, so yeah, I'd say you should get a little better than that. Driving habits make as much difference as anything, I baby mine down the road and rarely break 55mph.

No trailer = 12-15mpg


Air filter. All fluids. Tire pressure. Empty crap from bed. Brakes dragging. Locking gas cap. Thats what I can think of off the top of my head.

 

[TomCoppola]

I always baby the gas and still get really bad mileage. I do have bad compression on one of the cylinders but could that effect it?


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[SCOTTYINWV]

Yes, that could add to it.

Gear ratio and tire size can.
The load range of the tire, obviously 6 or 8 ply will get better mileage than a 10 ply.
Even tread pattern can.
Extra non essentials you carry in the truck.
Tire pressure
Winter blend fuel will cause you to loose 3-5mpg on average
Improper plug gap
Dirty air filter
Engine gunk and sludge
Water in fuel
The list goes on and on.


Changing trans, transfer case and diff fluids can help especially if switching to synthetics.
Routine maintenance can help. I see you have done a basic tune up.

One other thing often overlooked is the brakes dragging.

 

[IOWNJUNK]

If you have bad compression on one cylinder then 10mpg is about what I would expect you to get. Get that fixed before you attempt to see better numbers.

 

[TomCoppola]

Okay, thank you


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[twomanymontes]

That's about all I'm getting right now as well. And my truck is running great. When it warmed up for a few days 2 weeks ago, I jumped back up to 14 MPG.

 

[Ruger_556]

Is your speedo corrected?

 

[IOWNJUNK]

I know where you live, and I think the OP is from up north too, and maybe that has something to do with it. I have read in another thread about "winter gas" but didn't give it much thought, maybe its different in winter up there, I don't know. I can see just from the temp and driving conditions (longer warm up, defrosting, snow covered roads) getting a much lower mpg number than on a nice summer day.

Like this weekend when I go to the beach, 78'/sunny!!!