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Hummer recovery team
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Discussion Starter · #1 ·
I have a couple questions. First how manny gallon tank does a 97 Chevy silverado reg. cab short box have (24?). I have a 6in lift and 36in TSLs powered by a 5.7 and I am geting close to 6 miles to the gallon (city) even while driving the rig easy. This doesent feal right I have seen Stranglers post that said with his truck (454 and 37s) got around 12.

Does this sound right or am I geting screwed on gas mileage.
 

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iamfawkinwithyou
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20,722 Posts
You has problems, or your doing your math wrong. miles you drove/ amount of gas replaced in the tank.
 

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Little Member
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And the mileage may not be actual. A huge jump in tire size will throw off the speedo which in turn affects the odometer. If you went from the stock size of 265-75-16 which is roughly a 31" to a 36" tire can change your speedo by 10mph or so. You could figure the difference using a GPS.

As for the mileage being in the dumpster, there's more tire, and the truck is higher. Figure a good tune up with a fuel filter and checking the air filter would be a good start.
 

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Hummer recovery team
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2,086 Posts
Discussion Starter · #4 ·
And the mileage may not be actual. A huge jump in tire size will throw off the speedo which in turn affects the odometer. If you went from the stock size of 265-75-16 which is roughly a 31" to a 36" tire can change your speedo by 10mph or so. You could figure the difference using a GPS.

As for the mileage being in the dumpster, there's more tire, and the truck is higher. Figure a good tune up with a fuel filter and checking the air filter would be a good start.
My speedo is only like 3mph off if that. I have a new cool air intake and a Boss performance chip. I am sure it prlly. needs a fuel filter though. Pluss my gas gage is broke. But I can go only like 170 miles on 24 gallons of gas. :poke: I have a bad exhaust leake at the manifold though. Could that affect anything?
 

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circling the drain
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35,863 Posts
My speedo is only like 3mph off if that. I have a new cool air intake and a Boss performance chip. I am sure it prlly. needs a fuel filter though. Pluss my gas gage is broke. But I can go only like 170 miles on 24 gallons of gas. :poke: I have a bad exhaust leake at the manifold though. Could that affect anything?
at what speed? It is not 3 mph off at every speed. It is a % off at every speed.

You are traveling farther then your odometer says you are. (assuming stock gears and bigger tires).

6 mpg seems low, but its cold out, you have an older tbi 350 (assuming) You have a cold air intake (means nothing, I've never noticed them helping in mileage), a chip (which could hurt mileage), You think it needs a fuel filter, and it has an exhaust leak.

Doesn't sound anything like a well tuned engine for optimal mileage.

Strangler is running gears that match his tire size compared to his engine and the torque it makes.
 

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Hummer recovery team
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2,086 Posts
Discussion Starter · #6 ·
at what speed? It is not 3 mph off at every speed. It is a % off at every speed.

You are traveling farther then your odometer says you are. (assuming stock gears and bigger tires).

6 mpg seems low, but its cold out, you have an older tbi 350 (assuming) You have a cold air intake (means nothing, I've never noticed them helping in mileage), a chip (which could hurt mileage), You think it needs a fuel filter, and it has an exhaust leak.

Doesn't sound anything like a well tuned engine for optimal mileage.

Strangler is running gears that match his tire size compared to his engine and the torque it makes.
It was off 3mph at like 45mph. I do have stock gears also. Will the exhaust leak hurt mileage?
 

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Little Member
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A exhaust leak won't help mileage, but it wouldn't throw the mileage off that much if it was trashed.
 

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D.I.L.L.I.G.A.F.
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Will the exhaust leak hurt mileage?
If it's leaking before the O2 sensor it can.

My '98 ext cab Silverado was horrible on mileage but not as bad as yours. I got 12.5 mixed, 18-19 hwy. It had K&N CAI kit, new cat. converters and Summit cat back system (all with no leaks), new O2 sensors, new tune-up. I did everything I could think to get better mileage out of it and nothing made a difference!
 

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Premium Member
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5,237 Posts
Will the exhaust leak hurt mileage?
As CHVYPWR said, it will affect mileage if it is before the O2 sensor
Extra oxygen will be pulled in and past the O2 sensor giving a false lean condition, the computer will add some fuel to compensate.
 

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circling the drain
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35,863 Posts
It was off 3mph at like 45mph. I do have stock gears also. Will the exhaust leak hurt mileage?
Stock tires on that truck were approximately 30" or 31" tall. Going to 36's should put your speedo off more then that.

exhasut leak before the o2 sensor all other mentioned items.

It's NO wonder your mileage sucks.
 

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I'll Direc your TV
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8,828 Posts
Go through can clean your Throttle Body, replace the fuel filter, even the pump actually. Spark plugs, wires, cap/rotor. Basically all the normal engine tune up stuff like everyone says.

And definitally check your 02 Sensor, make sure your cat is working properlly too, if you have one that is, didn't see if you did or didn't
 

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Hummer recovery team
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2,086 Posts
Discussion Starter · #14 ·
An alignment was done after lift. Wires where replaced right after I got it. I feel it does need a tune up done. I do have the cats. still running into duels.
 

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I'll Direc your TV
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your cat should have a little indent on the bottom of it that looks like a big freeze lug. see if there is black soot around the edges, if there is that means that the cat is bad and needs to be replaced. That's what that thing is for, if the cat goes bad and clogs up, then it'll create too much pressure and that little plug is there the relieve that extra pressure.

my 91 silverado had the same thing, i just ran it like that, it's not my DD so i didn't care. That was before I cut the cat off anyway lol
 

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Hummer recovery team
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2,086 Posts
Discussion Starter · #16 ·
your cat should have a little indent on the bottom of it that looks like a big freeze lug. see if there is black soot around the edges, if there is that means that the cat is bad and needs to be replaced. That's what that thing is for, if the cat goes bad and clogs up, then it'll create too much pressure and that little plug is there the relieve that extra pressure.

my 91 silverado had the same thing, i just ran it like that, it's not my DD so i didn't care. That was before I cut the cat off anyway lol
I will have 2 check that. I got the back half of my exhaust done and they told me NO WAY dont cut my cats off on my 97.
 

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I like trees
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5,795 Posts
I will have 2 check that. I got the back half of my exhaust done and they told me NO WAY dont cut my cats off on my 97.
Im running true duals and headers with no cats on my 96 tahoe.But you have to buy the 02 simulators:thumb:
 

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End nerd persecution
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2,248 Posts
at what speed? It is not 3 mph off at every speed. It is a % off at every speed.

You are traveling farther then your odometer says you are. (assuming stock gears and bigger tires).

6 mpg seems low, but its cold out, you have an older tbi 350 (assuming) You have a cold air intake (means nothing, I've never noticed them helping in mileage), a chip (which could hurt mileage), You think it needs a fuel filter, and it has an exhaust leak.

Doesn't sound anything like a well tuned engine for optimal mileage.

Strangler is running gears that match his tire size compared to his engine and the torque it makes.
Actually its a Vortec 350. '96 was the first year. His math is definitely wrong. My '96 used to get aroung 14 around town with 6" lift and 35" swampers and stock 3:73 gears. I had a long bed so I'm not sure on the smaller tank size (~26 galllon for the small tank I think).
 

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I like trees
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5,795 Posts
Pm your vin and I can pull the build sheet on this for you.
 

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OUT FOR BLOOD
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49 Posts
i found on my wrangler if you take ur tire size divide it by the stock size then multiply that by the miles drivin you will get a closer number to what you are actually gettin.. with the bigger tires the odometer reads a diff number.. so take ur 36s/31(aprox. original tire size) that will give you how many more miles you traveled compared to wat your odometer reads... multiply that by the total number of miles driven... then take that number and divide it by total gallons you put in... thats a closer number to the right mile per gallon
 
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