'05 Impala 3.4 uses too much fuel !!!

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Here goes. 69,000 miles on base 2005 Impala 3.4. It seems the HIGH fuel usage started AFTER all new fuel lines we're installed.(as far as i remember). I can drive 30 miles and it uses about 1/8 tank or 1/4 tank (+ -) for round trip. so 15 miles 1/8 tank.
It runs fine.
Just changed spark plugs due to maybe that was a cause and they were worn out with a larger gap in them across the board. I just changed the fuel pressure regulator today and need to drive it some.
Sometimes a can smell a gas odor mostly not. New fuel filter also. Strange thing is if the car sits for a day the fuel gauge can read LOWER just by sitting...ok,that's crazy!
NO...i repeat...NO leaks underside with it running or not. Fuel pressure is fine.
It has run a bit lumpy at idle, it has taken a bit longer to start in the past (a few reasons i changed the F.P.R.). Mostly it has run very smooth where you would think it's not even running!
Plastic fuel tank so did the last shop maybe get a small crack in it when removing it for new lines ???
The passenger side tank strap is bad looking, the drivers side looks new.
(live in the snow belt).
There is NO dripping anywhere so where in the frigging world is the gas going???
I ran it today...shook the car to get the fuel sloshing in tank and no see leaks.
Been doing this for about 5 months or longer and oddly it seems AFTER the tank was dropped for new lines.
Had engine scoped...checked. All sensors are working in range as they should.
Many are stumped. The more fuel in tank the faster IT SEEMS to go out yet tank looks good...."looks good".
Thoughts ???
New tires within last 9 months. Drives straight. Brakes...well make some rattling sounds on/off.
Wheels spin freely.
I did have BOTH front hub/bearings changed with Moogs and BOTH drive axles. Just some fyi.
It used to not use much gas but...when it wasn't so old as it is now.
It does need the fuel filler neck/tube...it's real rusty !!
OK...Your turn !
 
Miles per 1/8 or 1/4 of a tank is completely meaningless.

What's the actual mpg? And how is it being driven? Conditions? Highway? City?
 
Never used so much fuel in the past,short trips or long. Eats more on longer trips and FASTER (max of 60 mph) and not doing that anymore of those trips. I CANNOT fill the tank or within a few days of short tripping it drops down FAST!
I could put x amount in and zero out trip to see what i get.
Seems to do better at 1/4 tank. Fill it up and POOF, vanishes.
Thinking coolant sensor or O2. Pcv valve has rivets in it so could i just grind them off and clean it? Air filter changed yearly.
Has plenty of power and no...not a lead foot person.
Heck, there have been times it's at 1/2 tank on the mark and i go to work and in a 2 days it drops 1/8 at least....that's wrong. 1/8 in 5 miles ?
I used to work further and fill it up and last TONS longer,maybe fill it back up in 2 weeks.
I'll try to get a mpg soon for you.
I will venture to say mpg has to be like 10 as is...so it seems.
Exhaust doesn't smell egg like but normal.
BUT car can just sit for a day and gas IS lower on gauge the next day. Figure that one out. I've put cardboard down for any possible leak spots...put foam sheets down (gas will eat foam)...all good.
I'll do whatever i can to help you great folks out.
 
Dropping the tank probably jostled the fuel pump and could have been enough to smoke the sending unit. Those Impala's have lots of issues with that. Have you made sure it's ACTUALLY using that much fuel, or is the gauge just wrong?
 
I want to speculate that if the engine was consuming that much fuel under normal driving conditions, you would feel the sluggishness, most likely it would throw a code.

I agree, don't go by the fuel gauge. Fill it up and drive it until it reads about 1/4 tank, then fill it back up. Now calculate the mileage driven to how much fuel you had to replace.
 
Like some others have said. Do a good mpg check. GM fuel gauges of that era are known to be problematic. You can keep guessing and replacing parts and still may not find the problem.
 
FWIW I got a batch of "bad" gas recently that only got 16 mpg in my daily driver 2000 Mustang 4.6 that I usually get 22 mpg with. Have you changed gas stations or tried different grades of gas?
 
Try a more precise method of measuring MPG. Top of tank to click and then next check do again to click and divide miles by gallon(s) used.

Your gas gauge is not linear and can change over time.
 
Does the dip stick smell gassy? Are the plugs wet and black? Maybe a leaky fuel pressure regulator or injectors? If gas isn't leaking externally, it is in the oil pan.,
Rant follows:
What is the unit cost of an access plate to the in tank stuff? Everyone who ever had to drop a gas tank just to replace a sender or pump would gladly have paid for it. AMC Jeeps, one of the most rinky dink car makers ever, had a cover. It was a 2 minute job to get to the sender , Same with my E28s . They even had a drain plug.
grin2.gif
 
You need to do this scientifically. Fill the tank and reset the trip odometer. Drive it until the gauge shows half or so. Fill up the tank again and mark down the number of gallons. Check the trip odometer and calculate the actual miles/gallon used, not what the gauge or onboard meter shows. Then decide what the fuel usage actually is. On further thing to check is the Evaporative emission system isn't drawing a vacuum in the tank as you drive or at random times. This would bow in the tank sides and create fluctuating fuel level indications.
 
Originally Posted by andyd
Does the dip stick smell gassy? Are the plugs wet and black? Maybe a leaky fuel pressure regulator or injectors? If gas isn't leaking externally, it is in the oil pan.,
Rant follows:
What is the unit cost of an access plate to the in tank stuff? Everyone who ever had to drop a gas tank just to replace a sender or pump would gladly have paid for it. AMC Jeeps, one of the most rinky dink car makers ever, had a cover. It was a 2 minute job to get to the sender , Same with my E28s . They even had a drain plug.
grin2.gif



To be fair, the '05 Impala has an access cover for the fuel pump. You can't, however, replace the lines without dropping the tank.
 
Filling the tank isn't going to make it go through gas any faster. It's the only way to accurately measure the mpg.

If you're worried about cost of filling the tank, it's going to cost the same regardless, as filling it rather than $10 or $20 at a time it's using the same amount of gas. Technically you might save gas by filling it as you won't have to drive to the gas station as often.
 
When they dropped tank I bet the gasket on fuel pump is pinched or torn. You won't see gas but you should be able to smell it. Sounds like evaporation from the seal. The tank could have a crack in it at the top again you should be able to smell it.
 
Ok. I replaced the fuel pressure regulator (known to be crap) and it has vastly improved. Fuel usage so far is way down not like it was.
Has a more zip in it's step along with fresh plugs.
No more gas smell. I still will get a mpg asap. Idles smoother too and no more lumpy running (when it would at times) nice a smooth to where you think it's not even running.
 
Sounds like you're chasing a nonexistent problem. If you aren't leaking fuel, and you have no driveability concerns, and lapscopes are all showing normal sensor operation, then you aren't using as much fuel as you think. As others have said, gm gauge of this era are almost arbitrary. I own your cars cousin, and the fuel gauge does the same thing. Your names not Joseph, is it?
 
Can not believe the OP has not had the MPG checked using the old school , real world method

The gas gage is just a " guess-o-meter " . Even the MPG display is a maybe a little more accurate guess
 
You're probably leaking fuel. I had a bad fuel filler hose but it only leaked when I was driving and the fuel sloshed around but the wet area dried quickly after I parked so that by the time I got under the car it looked dry, plus a bad filler neck would allow fuel to evaporate.
 
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