Thread: gas mileage is turrible. can anybody help with clues?

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  1. #1 gas mileage is turrible. can anybody help with clues? 
    GT Level Member Shiftingshaddow's Avatar
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    i'm getting 13 mpg. not too good. now, mostly i do city driving with some freeway and some highway for work. about 200-250 miles a week or so. when i first got the car i would get about 19-21 for the same type of driving.

    background info: 199950 miles on it. my fuel gauge does not work, nor does my DIC. Either the bulb is out or the unit does not work anymore. I have a can tune from ZZP and a 3.4 pulley and u bend delete with a cat and running al104 plugs. these have been on the car for between 1.5 years and 2 years. I put them on about a month or so after getting the car so there is history there.

    i know im getting 13 mpg by setting the trip when i get gas to zero, then running the car nearly out of gas either on purpose or accident and then dividing the mileage by the gallons i put in. for the record, its a 16 gallon tank but it will take 18 gallons if run dry. i put 17 in it semi regularly.

    i have no check engine light on the dash nor do any codes show up on torque pro scan with the android app.

    now, when i go up a hill the car wants to kind of, i don't know how to write it, spudder or something, like its having a hard time. the rpms dance, like 1000-1500 if you try to go at a steady pace (like 45 mph) up a hill. but if you accelerate it accelerates as normal.

    i would say the performance is down but the boost still works.

    checked vacuum lines, look all good and connected. i replaced them a year or so ago. the plugs n wires i replaced about the same time.

    things that make a small difference that i will put out up front: i warm the car up in the morning for 5-10 minutes when its cold (so i can sit in it). sometimes i eat lunch in it and keep it running when its really cold out. and finally, the tire pressure may be a little low. these should not account for the huge drop in gas mileage though.

    i have torque pro and can use it to observe whatever parameters it is capable of observing. having it idle in the driveway at operating temperature produced nothing crazy that i saw but i'm not really sure what i should be looking at and i need to take it for a drive and look but i need to know if i can find any clues by looking. i can see intake temperature, coolant temp, vacuum, boost, MAF, rpm, etc. maybe if i just know what normal parameters are i can check for them while driving.

    i could run some seafoam in it but i don't think that's going to solve the issue. i'm thinking its gotta be a sensor or egr valve. its not behaving like the cars i've had in the past that needed a new egr valve, though. no gas leaks at the rail or injectors or anything like that.

    i need to get this fixed asap and can't afford to just replace several sensors without knowing which one it is right now. i was hoping to make it to tax return and then do a lot of things at once but its not going to happen. anyone else ever have the same kind of symptoms?
    2001 GTP Special Edition
    ZZP DP with Cat, Open Cone Intake, ZZP 1.0 PCM, 3.4 pulley, AL 104s, Rocker Panel Delete.....
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  2. #2 Re: gas mileage is turrible. can anybody help with clues? 
    Killa Bee Scottydoggs's Avatar
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    i stopped reading at the plugs are 2 years old. copper plugs dont last longer then 15,000 miles. its time for new plugs.

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  3. #3 Re: gas mileage is turrible. can anybody help with clues? 
    GT Level Member Shiftingshaddow's Avatar
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    hmmm. easy enough. cheapest solution probably. i thought they'd get more than 1.5-2 years on them. no misfires either. but hey, if thats it, i'll take it.

    thanks for the suggestion.
    2001 GTP Special Edition
    ZZP DP with Cat, Open Cone Intake, ZZP 1.0 PCM, 3.4 pulley, AL 104s, Rocker Panel Delete.....
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  4. #4 Re: gas mileage is turrible. can anybody help with clues? 
    I live here. Slick2500's Avatar
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    Sounds like it needs a tune up.
    The gas tank is 17.5 gallons.
    Double check your plugs and wires.
    Double check for vacuum leaks.
    When was the last time you changed your fuel filter? On higher mileage cars you should change your fuel filter about once a year.
    On Torque you want to monitor your long term fuel trims bank 1 and short term fuel trims bank 1 they both should be 0 +/- 5 at idle.
    2003 Redfire Metallic Chevy Tahoe Z71 - Airaid Modular Intake Tube, Flowmaster Exhaust.
    Quote Originally Posted by The Sunfire Guy
    Superchargers take away horsepower
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  5. #5 Re: gas mileage is turrible. can anybody help with clues? 
    Turbo is the way to go. Fivefingerdeathpunch's Avatar
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    Clean the MAF sensor, might cure the rpm flutter issue and can bring back some mpgs if super dirty.

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  6. #6 Re: gas mileage is turrible. can anybody help with clues? 
    GT Level Member Shiftingshaddow's Avatar
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    i will start with changing the plugs and fuel filter. normally, i know a person would change the wires with the plugs but we're talking less than two years on the plugs n wires and 15-20k. that's 40 bucks i don't want to spend. and hopefully i can get them off without breaking them. but they are different plugs than stock so does that affect the wires more than normal somehow?

    vacuums are all good. checked couple days ago.

    i don't know how to clean the maf sensor. do i need to remove it and clean by hand with something or run some kind of cleaning agent in the vacuum lines?
    2001 GTP Special Edition
    ZZP DP with Cat, Open Cone Intake, ZZP 1.0 PCM, 3.4 pulley, AL 104s, Rocker Panel Delete.....
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  7. #7 Re: gas mileage is turrible. can anybody help with clues? 
    Turbo is the way to go. Fivefingerdeathpunch's Avatar
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    Maf sensor just has 2 screws holding it in place, they are torx style bits. Unplug the connector and remove the screws and take the sensor out, then just spray it down with MAF cleaner. Let it dry for a few minutes and re-install. They sell small bottles of cleaner for like 4 bucks at any auto parts store.

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  8. #8 Re: gas mileage is turrible. can anybody help with clues? 
    Killa Bee Scottydoggs's Avatar
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    id be ready to buy wires, they dont always come off in one piece.

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  9. #9 Re: gas mileage is turrible. can anybody help with clues? 
    GrandPrix Junkie SgtMarshal's Avatar
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    letting the car sit with the engine running is going to kill your miles per gallon. when I do mostly city driving I get around 12 mpg so I'm not sure how concerned I would be. my wife drives a newer model Ford Fusion with a 4 cylinder and it get about 16 in city only driving.
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  10. #10 Re: gas mileage is turrible. can anybody help with clues? 
    I live here. Slick2500's Avatar
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    Even Wal-Mart sells Mass Air Flow Sensor Cleaner.
    2003 Redfire Metallic Chevy Tahoe Z71 - Airaid Modular Intake Tube, Flowmaster Exhaust.
    Quote Originally Posted by The Sunfire Guy
    Superchargers take away horsepower
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  11. #11 Re: gas mileage is turrible. can anybody help with clues? 
    I live here. Slick2500's Avatar
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    Quote Originally Posted by SgtMarshal View Post
    letting the car sit with the engine running is going to kill your miles per gallon. when I do mostly city driving I get around 12 mpg so I'm not sure how concerned I would be. my wife drives a newer model Ford Fusion with a 4 cylinder and it get about 16 in city only driving.
    Right after I converted my gp to E85 we had an average temp of like 10* and I would let my car warm up for about 15-20 min each morning before work and my mileage only dropped down to 14 at the lowest.
    And before I switched the gp to E85 when I would let it warm up on cold days and use it for work 30-40 miles a day in town driving i would drop down to about 16 mpgs
    2003 Redfire Metallic Chevy Tahoe Z71 - Airaid Modular Intake Tube, Flowmaster Exhaust.
    Quote Originally Posted by The Sunfire Guy
    Superchargers take away horsepower
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  12. #12 Re: gas mileage is turrible. can anybody help with clues? 
    GT Level Member Shiftingshaddow's Avatar
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    when i realized how much gas i was using i cut my idling time in more than half. don't let it warm up nearly as long. its still drinking gas. with the poorer performance and the spuddering something has to be wrong.
    2001 GTP Special Edition
    ZZP DP with Cat, Open Cone Intake, ZZP 1.0 PCM, 3.4 pulley, AL 104s, Rocker Panel Delete.....
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  13. #13 Re: gas mileage is turrible. can anybody help with clues? 
    GT Level Member Shiftingshaddow's Avatar
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    Quote Originally Posted by Fivefingerdeathpunch View Post
    Maf sensor just has 2 screws holding it in place, they are torx style bits. Unplug the connector and remove the screws and take the sensor out, then just spray it down with MAF cleaner. Let it dry for a few minutes and re-install. They sell small bottles of cleaner for like 4 bucks at any auto parts store.
    do i need to spray inside it? or just spray the outside of it?
    2001 GTP Special Edition
    ZZP DP with Cat, Open Cone Intake, ZZP 1.0 PCM, 3.4 pulley, AL 104s, Rocker Panel Delete.....
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  14. #14 Re: gas mileage is turrible. can anybody help with clues? 
    I live here. Slick2500's Avatar
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    Spray it everywhere it looks dirty. Once it is clean stop spraying and let it air dry for about 5 min.
    2003 Redfire Metallic Chevy Tahoe Z71 - Airaid Modular Intake Tube, Flowmaster Exhaust.
    Quote Originally Posted by The Sunfire Guy
    Superchargers take away horsepower
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  15. #15 Re: gas mileage is turrible. can anybody help with clues? 
    Killa Bee Scottydoggs's Avatar
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    i got the 14 mpg blues too. its all local driving that does it.


    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  16. #16 Re: gas mileage is turrible. can anybody help with clues? 
    GT Level Member Shiftingshaddow's Avatar
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    at first i thought it was the idling. cutting it down didn't show much improvement. it used to get 19-21 with the same driving. i think when i put the light mods on it it went down an mpg or two. i mean, really, i've been trying to drive it like a grandma car to save gas and nothing is really helping.

    no gas mashing going on which means no fun and why have it? especially since its hitting the stage where crap is going wrong left and right, oil pan is leaking, crank will probably start leaking if it isn't already. which i'll probably be posting a thread in the next few months about it chewing axles up and pulling hard left when braking (i did replace the brake pads, rotors, and front calipers and it still does it) not holding alignment (ive replaced control arms, outer tie rods, sway bar links, hubs, axles (which keep going bad after a few months) motor mounts). eh, whatever, there it is. might as well post now i guess. what's left? subframe bushings? my luck the thing has a bent cradle or something.
    2001 GTP Special Edition
    ZZP DP with Cat, Open Cone Intake, ZZP 1.0 PCM, 3.4 pulley, AL 104s, Rocker Panel Delete.....
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  17. #17 Re: gas mileage is turrible. can anybody help with clues? 
    GT Level Member Shiftingshaddow's Avatar
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    Quote Originally Posted by Scottydoggs View Post
    i stopped reading at the plugs are 2 years old. copper plugs dont last longer then 15,000 miles. its time for new plugs.
    I think you nailed it. swapped them out tonight and took it for a little drive and it ran great again. they weren't worn down to the nub but they were definitely worn. so i'll check the gas mileage this week to confirm gas mileage. reused the wires. they came off fine since they were only on there for a year and a half. i probably put 15-20k on the plugs n wires. surprises me how fast those wear out.

    i attempted the fuel filter but the fuel line nut was rusted and it wouldn't come loose with vice grips so i said screw it. don't want a broken fuel line to mess with. save that for later or just pay the shop on that.

    i also went to buy the maf cleaner and it was almost 9 bucks at advance so i let that slide today and i'll get some cheaper stuff at the wmart.
    2001 GTP Special Edition
    ZZP DP with Cat, Open Cone Intake, ZZP 1.0 PCM, 3.4 pulley, AL 104s, Rocker Panel Delete.....
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  18. #18 Re: gas mileage is turrible. can anybody help with clues? 
    GrandPrix Junkie SgtMarshal's Avatar
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    I think the wires last longer than the plugs, but the last time I did plugs I ended up breaking two wires so I just changed all my wires at the same time. I changed my plugs about a month ago, and I will never buy the iridium plugs again. they didn't last anywhere near what they were supposed to and there was no difference in power/fuel economy. its hard to beat 10 bucks for a set of plugs.
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  19. #19 Re: gas mileage is turrible. can anybody help with clues? 
    GT Level Member Shiftingshaddow's Avatar
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    i had to put the copper al104s in it because of the 3.4 pulley. the day i put the pulley on and went wot it dun reel bad on stock grade plugs. the 104s are colder spark. looks like thats going to be a yearly job. bright side is the wires come right off and the plugs come right out and its not so messy in there. they were only 12 bucks or something.
    2001 GTP Special Edition
    ZZP DP with Cat, Open Cone Intake, ZZP 1.0 PCM, 3.4 pulley, AL 104s, Rocker Panel Delete.....
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  20. #20 Re: gas mileage is turrible. can anybody help with clues? 
    GrandPrix Junkie SgtMarshal's Avatar
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    I use the copper 104s as well, I'm sure a lot of people do
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