Gas mileage decline

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Jul 31, 2019 | 09:53 AM

CosmoC5

Thread Starter

Cruising

Joined: Jul 2011

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Gas mileage decline

99 Corvette 49k miles, 28mpg to 24mpg. air filter replaced recently

Jul 31, 2019 | 11:35 AM

Not4spd

Melting Slicks

Joined: Nov 2008

Posts: 2,185

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From: Garland TX

The first thing I would replace is the fuel filter as it will become clogged over time.

Jul 31, 2019 | 01:19 PM

mrlmd

Drifting

Joined: Jun 2013

Posts: 1,969

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From: Shell Point (Crawfordville) Florida

Is your foot getting heavier?

Jul 31, 2019 | 01:27 PM

acroy

Race Director

Joined: Jun 2013

Posts: 12,414

Likes: 1,750

From: DFW TX

Dump a can of seafoam in 1/4 tank of gas and run it out
Check spark plugs and wires
those are the easy things

Jul 31, 2019 | 01:30 PM

My Vette Life

Safety Car

Joined: Mar 2015

Posts: 3,638

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Quote:

Originally Posted by CosmoC5

99 Corvette 49k miles, 28mpg to 24mpg. air filter replaced recently

Just start with a basic tune up.

Plugs
Clean maf and TB

28mpg to 24 is nothing to worry about, i cant even get 18mpg and cruise at 16mph on a regular.

Jul 31, 2019 | 07:44 PM

Tenshots1

Advanced

Joined: Jan 2019

Posts: 86

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24mpg is still crazy good. Must never touch the city! My vette never gets over 20mpg with a good amount of freeway driving, except for the time we drove to vegas and got 28mpg.

I challenge you to have fun with your vette and get the mpg down to about 20mpg.

Jul 31, 2019 | 07:57 PM

C5 Diag

Moderator, Tech Contributor

Joined: Sep 2013

Posts: 15,644

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From: Cape Coral, Florida

Without a scan tool to look at fuel trims, MAF sensor, etc to nail it down...ready, aim, fire !...load the parts canon !!

Jul 31, 2019 | 08:27 PM

3sACROWD

Melting Slicks

Joined: Sep 2011

Posts: 2,258

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From: Appleton WI

Is the car idle rougher than before the filter change? How dirty was the filter? Check the connections from the filter to the intake. Also consider cleaning the MAF.

Any other symptoms like loss of power? Did you recently fill with fuel?