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awful mpgs

This is a discussion on awful mpgs within the General Help forums, part of the LSx Technical Help Section category; my car has less than 50,000 miles, and for some reason im getting on average less than 250 miles per ...

  1. #1
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    triple black
    02 z28 m6

    awful mpgs

    my car has less than 50,000 miles, and for some reason im getting on average less than 250 miles per tank. normally i can get over 400. how often do spark plugs go bad on ls1s? would running lean cause mpg issues?

  2. #2
    Member 180ls1's Avatar
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    1998 Firebird Formula WS6

    check your o2's, maf, and plugs/wires. but your plugs should be good you never know when they will go same with your o2's and maf. lean should not ccause that problem running rich should. didi you get any codes or did you change anything around with your car?
    1998 Firebird Formula WS6... few things done.

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    TunedbyFrost.com Tuner Frost's Avatar
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    almost certainly O2s; they control almost all of your cruise fueling. They should be changed at a minimum of 40k miles anyhow.

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    Simpsons Did it!! 98formy's Avatar
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    83 Z28 new project
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    Quote Originally Posted by emotionalpiracy View Post
    my car has less than 50,000 miles, and for some reason im getting on average less than 250 miles per tank. normally i can get over 400. how often do spark plugs go bad on ls1s? would running lean cause mpg issues?
    I have an a4 and I wish I could get 400 miles to a tank. I am lucky if I get 225 to a tank driving it nice, then again, I am not stock either.

  5. #5
    Moderator Firebirdjones's Avatar
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    Frost is correct,,,,02's are considered "tune up" items and should be replaced at regular intervals.

    They do get lazy over time,,,

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    79 T/A -91 Firebird
    1998 Trans Am -Oynx Black

    Ive get horrible gas mileage as well... my rear 02's are gone(cats) and my egr code is on..... so im gonna get rid of the AIR and EGR system.. and change the 02 sensors......... which brand is the best guys???

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    Senior Member 35thAnniZ28's Avatar
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    eating bulldog
    son of biscuit

    i got some ntk's from summit which came out to 110 altogether i think..their smaller and fit alot better with the headers i got

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    79 T/A -91 Firebird
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    Cool. Would a faulty EGR system rape gas?? if so.. its gone ASAP..

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    Senior Member 35thAnniZ28's Avatar
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    eating bulldog
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    i heard removing the egr system wouldnt affect it..but not sure..wait until frost signs on..he's an expert on the ls1 computer

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    79 T/A -91 Firebird
    1998 Trans Am -Oynx Black

    My car is daily driver and i have to drive 1/4 mile to work each way.. so im not really worried to much about extreme power adding, Just something i can kill ponies and ricers on the weekends. My EGR is out and i thought I would clean up everything and kill emissions all together..

  11. #11
    Moderator Firebirdjones's Avatar
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    Quote Originally Posted by JoshieDoom View Post
    My car is daily driver and i have to drive 1/4 mile to work each way.. so im not really worried to much about extreme power adding, Just something i can kill ponies and ricers on the weekends. My EGR is out and i thought I would clean up everything and kill emissions all together..
    A 1/4 mile??? I wouldn't even bother starting the car for that,,,,I'd be footin' that,,,,or at the very most ride a bike. sheeesh.

  12. #12
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    I just went through the SAME thing two weeks ago..Check out my posts on it. PCM showed no codes, mileage dropped from 350 to 200-225 a tank.

    Spent $400 on new irridiums, wires, feil filter, air check valves..etc. Still no change in mileage.

    Changed both o2's, mileage was fine.

    I have an extra set of AC Delco O2's if you are looking.

    GM Charcoal, Emissions, O2 etc.

  13. #13
    TunedbyFrost.com Tuner Frost's Avatar
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    Quote Originally Posted by JoshieDoom View Post
    Cool. Would a faulty EGR system rape gas?? if so.. its gone ASAP..
    Nah...

    The reason to almost always suspect O2s is like I said, they control almost all fueling of the car. The areas they do NOT control include startup and a few seconds after that (more than a few seconds if cold), and WOT. So, if your car is not in one of those 2 areas, the O2s are updating the mixture continuously. The other rub of them is that they don't usually fail outright, they usually get lazy and out of range. so you think they are still good.

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    triple black
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    id buy em off you but itll only cost me 106 to get them replaced without me having to do any work

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    $106 for two new O2 sensors? Even with employee discount through friends at NAPA and Autozone, cheapest I could get was $63.99 and that was Bosch. Internet search was the same price.

    Disbelief...

    You should learn how to work on your car. Sensors take maybe 10 minutes to change out and it is real easy. A real good project to start.....OK, I'll shut up.

  16. #16
    Moderator Firebirdjones's Avatar
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    Quote Originally Posted by emotionalpiracy View Post
    id buy em off you but itll only cost me 106 to get them replaced without me having to do any work
    You replaced them already???? Man thats quick, you just posted this thread on the 17th,,,,you're quicker than I am,,,maybe I'm getting old,,,lol.

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    79 T/A -91 Firebird
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    If you have ever walked a 1/4 mile in kentucky 8 degree winter weather in the woods your pretty frikin awesome

  18. #18
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    triple black
    02 z28 m6

    warranty at the place i bought it has a $100 deductible
    anything not covered in warranty i do with my friends.

  19. #19
    old timer blue02Z's Avatar
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    Quote Originally Posted by emotionalpiracy View Post
    my car has less than 50,000 miles, and for some reason im getting on average less than 250 miles per tank. normally i can get over 400. how often do spark plugs go bad on ls1s? would running lean cause mpg issues?
    400 miles to a tank?!?!?!? OMG! if i drive normally i get around 225 a tank. EVERYTHING on my car is up-to-date except the o2's. i didnt know they needed to be replaced like that. i need to get new ones, i have 75k.



    sorry for the hijack, but hey Frost, i pulled the fuse on my AIR pump it thru the Check engine code which i knew it would. but what will it do if i drive it with the light on? thanks

  20. #20
    Senior Member Bottesini's Avatar
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    Quote Originally Posted by blue02Z View Post
    400 miles to a tank?!?!?!? OMG! if i drive normally i get around 225 a tank. EVERYTHING on my car is up-to-date except the o2's. i didnt know they needed to be replaced like that. i need to get new ones, i have 75k.



    sorry for the hijack, but hey Frost, i pulled the fuse on my AIR pump it thru the Check engine code which i knew it would. but what will it do if i drive it with the light on? thanks
    If you are close to stock getting over 300 a tank on an 02 should be pretty easy (bigger tank in the 02). If the SES light is just from the AIR pump you should not have any problems other then getting annoyed from the light. I know I had mine running for a while when I was running with no cats, for a while I kept freaking out when I looked down and saw the light on, but that was purely from instinct. The red from the odometer still catchs me off guard sometimes

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