Fuel mileage way down

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Stevea100m

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so guys here is what I have going on, I have a 95 k2500 with the 5.7 and a 4l60e. The problem I have is the mileage is in the tank. I mostly do highway miles for work and I'm getting about 13 with premium. I tried dropping to mid grade and it dropped to like 9. I get a slight surge at medium acceleration while going down the road. Where should I start?
 

michael hurd

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Perhaps your expectations are a bit out of touch with reality.

You own a 22 year old truck that has larger tires than it was equipped with from factory, likely a tired engine and questionable modifications.

Things that can cause poor economy:

Poor alignment
Low tire pressure
Worn suspension components
Brakes dragging ( stretched return springs in drums, brake calipers sticking, or a brake hose inner liner collapsed, e-brake cable seized on )
Driving fast
Oversized tires
Cool air temperature ( warmer air has less drag )
Low engine coolant temperatures
Wheel bearing / axle bearing issues
Lock up torque converter that doesn't lock
Short trips around town / drive thru's
Catalyst brick melted / partially blocked
Worn distributor or timing chain issues


and a myriad of other possible causes.
 

Stevea100m

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Well I would tend to agree but I have done a complete tune up, put a high flow cat and offroad Y pipe on it, Did the TBI mods all the while the mileage never increased. I was thinking possibly a bad sensor but I don't have a scanner to verify it.
 

df2x4

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First of all... Why are you running premium and mid-grade? Unless you've got some serious work in under the hood there's absolutely no need for that.

Granted both of my trucks are Vortecs, but the few times I ran 91 or 93 octane on the stock tune in my red truck it ran like garbage and killed my mileage. The tune on these trucks expects 87.

Also, don't expect any performance mods like the exhaust to help your mileage any, it won't. At least not to any noticeable degree.
 

df2x4

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Im running premium because on the lower grade fuels it gets even worse mileage!

If you've run premium for any length of time the PCM may be adjusted to it, hence the perception that your mileage is worse on 87. If I were you the first thing I would do is switch back to 87 and run at least two full tanks through it to allow the PCM to re-adjust.
 

Stevea100m

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I will give that a shot but that still doesn't explain the surge when at cruising speed under just the slightest acceleration.
 

Justin S

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Is your truck OBD1 or OBD2? I was just writing a long response on what to try next but I was assuming it was OBD1, so figured i'd ask that first haha
 
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