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mpg what's average in city I only get 10 miles per gallon!!!

This is a discussion on mpg what's average in city I only get 10 miles per gallon!!! within the Firebird / WS6 forums, part of the Vehicle Specific category; I have a 1998 ws6 and I only get 10 miles per gallon in city and maybe around 20 in ...

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    mpg what's average in city I only get 10 miles per gallon!!!

    I have a 1998 ws6 and I only get 10 miles per gallon in city and maybe around 20 in highway was wondering if that's normal..I have a few bolt on..long tube header, slp lid, frost tune..just changed the spark plug but haven't tried to see of mpg inproved

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    Senior Member theorangeguy's Avatar
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    is it an automatic or manual...? either way that seems a little low. I can get 26-28 doing 70-85mph on the interstate but mine is a 6speed.

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    It's a six speed

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    you have an issue somewhere....mpg's should be a lot better than that. How old are the O2's? Do your exhaust tips have a lot of soot?

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    Senior Member theorangeguy's Avatar
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    Quote Originally Posted by 0rion View Post
    you have an issue somewhere....mpg's should be a lot better than that. How old are the O2's? Do your exhaust tips have a lot of soot?
    ^^he's on the right path. does your car have catalytic converters on it? If they are old or clogged that could very well be part of the problem...out of curiosity, have you ever cleaned your mass air flow sensor?
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    1998 ws6 trans am

    It's a six speed

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    Yea I just recently put on sensors and new cats because I didn't have none and you know how laws are in cali..yes I cleaned mass airflow last month

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    how long have you had the car and has the mpg's always been that bad? You say you put cats on it....any chance it has mods you're not aware of?

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    Might have other mods on it only had the car for about a year and gas mileage has always been this bad..mods that I think has is an ls6 intake, long tube headers, maybe cam and fuel injects 35 lbs not to sure I'm kinda new to all this

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    Spaz is My Mentor SMWS6TA's Avatar
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    98 T/A w/a little mods...

    Might want to data log it, if you had mods on it like a cam or heads may not have been tuned properly....Some ppl will pull their mods and not retune it when they go to sell.

    Also 35lb injectors are not stock.

    Just throwing spitball ideas out...
    Last edited by SMWS6TA; 06-10-2014 at 12:38 PM.

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    Senior Member theorangeguy's Avatar
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    what kind of air filter do you have...? has it been replaced recently? sounds to me like the computer is changing the fuel ratio for some reason...seen vacuum leaks cause issues like this.

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    Quote Originally Posted by ws6shine View Post
    Might have other mods on it only had the car for about a year and gas mileage has always been this bad..mods that I think has is an ls6 intake, long tube headers, maybe cam and fuel injects 35 lbs not to sure I'm kinda new to all this
    does the car have any lope to it? It does sound to me like you might have some unknown mods there. In your first post you said you have a frost tune but if you have mods that you/he wasn't aware of then the tune would be off.
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    Has a k and n airfilter..has no vacune leaks check all of the car..the guy at tune by frost told me my computer had a tune already so he said it would be better to leave that tune because u wasn't sure what my car mods were but he did say there was some iregularity and the Rev limiter was set at 7k

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    35 lbs injected are not stock? I didn't know would that cause the car to waste more gas, the car run great has a lot of power the only problem is that mpg is real bad

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    right.....35's aren't stock. Stock is 28's. That leads me to believe you either have or had a cam or something....perhaps it was forced induction that they took off. Tough to tell. I would definitely say that's the root of your mpg issue though.

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    Surprised no one has asked this but what are your driving habits? Do you floor it or have heavy foot syndrome?
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    Quote Originally Posted by 98TransAmWs-6 View Post
    Surprised no one has asked this but what are your driving habits? Do you floor it or have heavy foot syndrome?
    10mpg would be hard to hit even with heavy foot syndrome and since he's concerned about mpg's I assume he's not flooring it everywhere he goes. He has a frankencar.....there are mods on there he doesn't know about or a tune for mods he no longer has.

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    Senior Member Naaman's Avatar
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    Quote Originally Posted by 98TransAmWs-6 View Post
    Surprised no one has asked this but what are your driving habits? Do you floor it or have heavy foot syndrome?
    I stomp the gas through 2nd gear, and into 3rd at least twice a day, and I pull away from almost every red light with great enthusiasm. I realize about 23 mpg combined city/highway, or, about 320 miles before I turn in for gas (usually around 13 gallons to reach a full tank).
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    10mpg would be hard to hit even with heavy foot syndrome and since he's concerned about mpg's I assume he's not flooring it everywhere he goes. He has a frankencar.....there are mods on there he doesn't know about or a tune for mods he no longer has.
    I know some people who floor it everywhere and wonder why their mpg's suck so I figured I'd ask the question. I do realize that would be pretty hard to hit but since it seems that there are mods or a tune for mods he doesn't have or he doesn't know about it could be a combined issue.

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    mpg what's average in city I only get 10 miles per gallon!!!

    98's have a 14 gal steel tank. Smaller than the later yrs. The 35 lb injectors with mild bolt ons would be where I'd start. To answer your question = yes having higher injectors with a different program tune can effect the engine greatly. The injectors are an electronic control part. If the ecm tells applies currect, the amount of fuel dropped varies from 28lb vs 35 lb. More fuel will be dumped. Now if you add too much fuel yourplugs willfoul out. Pull a couple and look at them. Are they white or black? Smell like gas? Black & smell like gas, they could even be wet are all indicators of fuel rich. Your Ecm & O2's can only compensate so much.
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