This is Rather Something Unusual (I Think), I don't know if it happens to any body else, Any Other Impala Or Any Other Car For that Matter?, Because EVERYTIME I Brake to Stop The Car, I See My Gauge Needle Just Go Down, Whether I'm Braking From Going Fast Or Going Slow, But I Notice The Gas Wasting From Braking When I'm Going A Little Faster, Say Above 50 mph. All The Car Wants is For Me To Keep Going And Going And Never Stop, Cos If I'm Just Mashing On The Gas Pedal, The Car is Happy And Gas Gauge Needle Just Stays Put, I Can Drive 15-20 Miles Without the Needle Moving (And in Most Cases, The Needle Goes Up Instead Of Down When I'm Moving/On the Gas Pedal). But As Soon As I Start Braking, It Feels As If I'm Just Dumping The Gas Out, as the Fuel Gauge Needle Just Comes Flying Down. It Really Baffles and Worries Me, I Go Through $60 Gas Every Week ($20, 3 X/Week), Even When I'm Not Going AnyWhere else Other than Back & Forth to Work Which is Less Than 7.5 Miles One Way And I Do That Only About 5 Days A Week. So Whats Going On? I Closely Monitored This With My 2000 Bonneville With The Same 3800 Engine, The Bonneville Seem to Do Better with Gas Than The Impala (-->> For an Older Car). Not Saying The Bonneville is WithOut its One Flaw, The Bonneville Wastes Its Own Gas as Well Whenever I'm Banking A Curve, Such as Going in Or Leaving An Exit, I Just Watch The Gas Needle Come Flying Down And In Most Cases, Never Go Back Up When I'm Established And Going Straight On The Road Again. I've Owned About 5 Domestic Cars (3 Intrepids and 2 GM Cars) They All are Terrible With Fuel Economy. I Don't Think Foreign Cars Do This. The 3800 Engines (I'm Talking About The Non-SuperCharged Engines) are Rated Between 17-18 MPG in City And 26-27 MPG On HWY, But I, Doubt Those Figures are True, Cos I Get NoWhere Close to 17 Or Even 16 MPG in City Driving (And I Try to Brake Less, Whenever I'm Driving)
So I'm Just Curious if this is Normal, If AnyBody Else is Having This Problem?

YouTube Vid Link :

the needle going down is normal, the sender is toward the rear. the gas doesnt go anywhere. if you are hard on the gas pettle your mileage will be in the teens. i also know plenty that can get 30'* driving like a egg is under the petal with the na 3800

I find it hard to get good mileage in my car (3800 series 3) unless I'm careful. A bit of spirited driving will definitely make the needle drop quick.

Needle movement is caused by fuel sloshing around in your car, accelerating and hard stops will cause this....in fact, turn key to on, car not running, and have a couple of your buddies make that rear end go up and down repeatedly and watch your needle for movement...

Gas mileage is a product of the condition of the running engine, whether it'* city or highway driving, whether it'* hilly terrain, and mainly, the way you personally drive....if you are a jack rabbit driver on take offs, and tend to tail gate, and have to repeatedly hit your brakes, your mileage, dramatically goes down....

3800'*, if driven correctly, easily get close to 30 mpg on the highway, even with a LeSabre/Bonny.....

i know a few people who get 33 in h -body, my wife gets 28 in our sse, but there is alot of stops on her commute and she always has the a/c on

I was thinking the same thing but I have to replace the map sensor on my car

So You have the Same Problem With Your Gas?
Have You Narrowed The Issue Down To A Map Sensor?
If You Change It And It Helps You, Can You Please Do Come Back and Let Me Know If It Helped Your Case?
Thanks.

I'm due to receive the part in the mail on Monday and I'm gonna put it on and see How it does and I will let you know....my gas is terrible!

I don't know if the factory engines in the 9C1s are any different than any other Series II, but if they truly make 200 hp as rated (according to my info anyway), seems to me they are high enough compression to require premium.

The Grand Nationals of the 80s made about 200 hp with the same displacement. The Series II is derivative of the same engine (shorter piston rods and such) and they required premium. Just a thought, might try premium for a few weeks and see if it improves.

Afterthought here, I once owned an 88 Park Ave with a Series I 3800 and it got 30+ highway. MAP sensor could certainly screw with fuel economy if you know it has a problem, but make sure there are no existing ignition or fuel system component problems. I once saw one of my own vehicles gain 4 mpg from a couple cans of SeaFoam in the tank, and another 3-4 from SeaFoam in the crankcase. (Change oil IMMEDIATELY after running for 30 minutes).

Side note... WHY is there no way to edit your own post in a thread?