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serious bad fuel mileage.NEED ADVICE..HELP!!!!!

This is a discussion on serious bad fuel mileage.NEED ADVICE..HELP!!!!! within the General Help forums, part of the LSx Technical Help Section category; hello everyone, Im fairly new to the community but if theres a place where i can find someone to help ...

  1. #1
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    sunset orange metallic
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    Cool serious bad fuel mileage.NEED ADVICE..HELP!!!!!

    hello everyone,
    Im fairly new to the community but if theres a place where i can find someone to help me out with my problem its here.let me start by giving you a history in my car. its 2001 ws6. bought it used. i never had any real problems with it. bought it back in 2001. car ran great and gave me great mileage. sometimes it gave me as close as 33 mpg in the highway. it was sweet for a 6 speed. about 2 years ago i decided to stop making it my daily driver and only drive it for special ocassions. i also started buying alot aftermarket parts and storing them away. but before i parked it i bought a small so-called chip that would give you about 15hp more and about 5 mpg more. i thought sweet. more power more gas. this chip was a simple resistor that was inside a plastic box and it had 2 wires that came out of it. the wires would hook up to either the IAT or the CTS sensor, depending on your car model and year. Mine was suppose to go to the CTS. Also, at the that time the only other mod i had was an old SLP MAf sensor that had no screen that always triggerd my check engine light. with that MAF the car never gave me any problems. anyways, i installed this chip and i noticed two things right away. the first one was the check engine light turned off ! I was like wow this 20 dollar mod really works and and i also noticed better throttle response,however i noticed the gas went from giving me well over 430 to the tank to 150!...big difference...I emailed the company aabout the new problem and they told me to switch the wires, in other words swap them on the CTS sensor(black on color and vice versa). well, i dont remember if i did but i believe i didnt, but what i did do was take the chip off completely and i disconnected the battery for a whole week with the hopes of resetting the computer back to its precious setting. after connecting the battery a week later i noticed the check engine light came back on! so i thought it was back to normal since my car always had that light on due to the SLP maf with no screen. I parked the car away for a several months and i would start it here and then and then i decided to take it to work again just for like a couple months since i was getting close buying all the parts i wanted. when i started to drive it i noticed the gas economy was still bad....my fuel pump was good. the car never died on me and it never had trouble starting but yet my gas was bad...power was still great..

    so I ignored the problem because Id figured I was gonna practically change my engine and get it tuned...id figurded that with the computer tuning this was gonna go away if it was a computer problem and with a new fuel pump, fuel injectors, etc.. if this was part problem than this would go away...

    that was about a year ago..just recently i swapped my block into a bigger 421 and i installed my aftermarket bolt ons....I had a complete mail order tune from texas speed...i filled it up thr gas tank and after driving it 48 miles and im down to half a tank...realistically i knew that when I upgraded to a 421 block with all aftermarket parts, like MS3 cam, ported heads and, professional manifold..etc...i knew my gas mileage wasnt gonna be 31 mpg...but come on 100 miles to the tank just doesnt add up..by the way this is with easy driving since im still breaking in the engine. I need your help i know theres gotta be someone out there that can lead me in the right direction. The only other thing i forgot to mention is that i did put aftermarket bullet rims that make your wheels stick out more..ive heard that sometimes that kills your gas mileage but I doubt its that. I thought about changing the internal fuel pressure regulator but i havent done it yet...i dont want to buy parts that i may not need....somehow i believe its a computer thing since it started happening around the time i installed that chip but could be wrong..please help out..your help is gonna be truly appreciated

    jesse

  2. #2
    Spaz is My Mentor SMWS6TA's Avatar
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    OP, the reason this hasn't been notice is because it is in the wrong section. Should be move to the tech section. I'll see if a mod will move it so that others can see it.



    To help me and others please list all bolt-ons you indicated you have.

    Your problem - it could be a range of things. I know no help there. Based on what you posted these are the few things that come to mind.

    - Have you check for a fuel leak? Check everything, fuel tank, lines filter. Check it while running, it may be in such a spot that it can only be seen while under pressure.

    - Fuel consumption - only time I've seen that much change was due to fuel being pumped with to high of pressure, incorrect timing, or the injectors have gone bad. Most time if it is the injectors, hydrolock usually happens.


    - CEL (Check Engine Light) - can you get a code reader and post up the codes? That will help a lot.

    - MAF - Have you had it checked out? Dirty MAF or a bad MAF will effect fuel consumption, cause stalling or bog the motor down. Any alterations to the MAF and you're asking for problems. If the thin wires are messed up, again it will cause all sorts of problems. If you have the OEM MAF or know a buddy that has a simular model/yr see if he'll let you run it on yours.

    - Chip - I've never seen a chip that works on our cars and it turn out well. You could have fried the cts sensor (I think you are reffering to the O2's right?) and that will effect fuel consumption if it is on the front O2's. Code reader will let us know this.

  3. #3
    Moderator Firebirdjones's Avatar
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    Wow, alot is going on here.

    When was the last time 02's were changed? Those need to be changed every 40-50,000 miles. They are a wear item just like spark plugs and are the key factor in trimming fuel. As they get lazy mileage suffers.
    I would also get the car to a dyno tuning facility and get a more accurate tune, especially since we are talking heavily modded and large cubes. I'm sure the mail order tune is working, and it's probably good enough to buzz around and get some easy miles on it. But to really nail it down it needs to be monitored on a chassis dyno, or on the street with a wideband and tuning software.
    There are alot of tuning tricks to gain mileage, but I've found mpg just by fine tuning the AFR with a wideband for a more steady stoich reading. Takes time. Some of those cells jump all over the place and cause the computer to really search around for 14.7, that hurts mileage and throttle response.
    I'm no tuning genius with these computers, but I'm betting you'll find quite a bit left to change in that tune when you get it on the machine.

    Other things affect mileage as you know, the usual tire pressure is a big one, plugs, wires, fuel filter, air filter, dirty MAF etc....but I assume you've been through that with this engine swap.

  4. #4
    Spaz is My Mentor SMWS6TA's Avatar
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    FBJ, I tried PM'ing this to you last night but it said your mailbox was full. You where the 1st person I though of that could help this guy.

  5. #5
    Moderator Firebirdjones's Avatar
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    Quote Originally Posted by SMWS6TA View Post
    FBJ, I tried PM'ing this to you last night but it said your mailbox was full. You where the 1st person I though of that could help this guy.
    Oooops, sorry. I'll have to check that thing and clean it up. Thanks.

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    Senior Member redbird555's Avatar
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    Quote Originally Posted by jesus01pontiac View Post
    hello everyone,
    Im fairly new to the community but if theres a place where i can find someone to help me out with my problem its here.let me start by giving you a history in my car. its 2001 ws6. bought it used. i never had any real problems with it. bought it back in 2001. car ran great and gave me great mileage. sometimes it gave me as close as 33 mpg in the highway. it was sweet for a 6 speed. about 2 years ago i decided to stop making it my daily driver and only drive it for special ocassions. i also started buying alot aftermarket parts and storing them away. but before i parked it i bought a small so-called chip that would give you about 15hp more and about 5 mpg more. i thought sweet. more power more gas. this chip was a simple resistor that was inside a plastic box and it had 2 wires that came out of it. the wires would hook up to either the IAT or the CTS sensor, depending on your car model and year. Mine was suppose to go to the CTS. Also, at the that time the only other mod i had was an old SLP MAf sensor that had no screen that always triggerd my check engine light. with that MAF the car never gave me any problems. anyways, i installed this chip and i noticed two things right away. the first one was the check engine light turned off ! I was like wow this 20 dollar mod really works and and i also noticed better throttle response,however i noticed the gas went from giving me well over 430 to the tank to 150!...big difference...I emailed the company aabout the new problem and they told me to switch the wires, in other words swap them on the CTS sensor(black on color and vice versa). well, i dont remember if i did but i believe i didnt, but what i did do was take the chip off completely and i disconnected the battery for a whole week with the hopes of resetting the computer back to its precious setting. after connecting the battery a week later i noticed the check engine light came back on! so i thought it was back to normal since my car always had that light on due to the SLP maf with no screen. I parked the car away for a several months and i would start it here and then and then i decided to take it to work again just for like a couple months since i was getting close buying all the parts i wanted. when i started to drive it i noticed the gas economy was still bad....my fuel pump was good. the car never died on me and it never had trouble starting but yet my gas was bad...power was still great..

    so I ignored the problem because Id figured I was gonna practically change my engine and get it tuned...id figurded that with the computer tuning this was gonna go away if it was a computer problem and with a new fuel pump, fuel injectors, etc.. if this was part problem than this would go away...

    that was about a year ago..just recently i swapped my block into a bigger 421 and i installed my aftermarket bolt ons....I had a complete mail order tune from texas speed...i filled it up thr gas tank and after driving it 48 miles and im down to half a tank...realistically i knew that when I upgraded to a 421 block with all aftermarket parts, like MS3 cam, ported heads and, professional manifold..etc...i knew my gas mileage wasnt gonna be 31 mpg...but come on 100 miles to the tank just doesnt add up..by the way this is with easy driving since im still breaking in the engine. I need your help i know theres gotta be someone out there that can lead me in the right direction. The only other thing i forgot to mention is that i did put aftermarket bullet rims that make your wheels stick out more..ive heard that sometimes that kills your gas mileage but I doubt its that. I thought about changing the internal fuel pressure regulator but i havent done it yet...i dont want to buy parts that i may not need....somehow i believe its a computer thing since it started happening around the time i installed that chip but could be wrong..please help out..your help is gonna be truly appreciated

    jesse
    I'm not saying it was the whole cause of the issue but slp maf never helps really and has been known to cause all sorts of issues from poor fuel economy to CEL. Also the resistor they gave you just slips into the sensor and tricks the computer into thinking the ambient temperature outside is something around 34 degrees iirc which makes the computer trim the engine differently again not the best way to get HP or mpg. The stock MAF sensor is good to around 500 hp so if your really addement about modding your maf sensor throw the stocker back in there and just take out the screen.

    Also a mail order tune is not good at all for a custom stroker motor you need a complete dyno tune. A good tuner will be able to monitor all the fuel trims and correctly tune the engine in all parameters. What is the setup with the 421? Like cam heads intake etc? Also dont waste your time with the fuel regulator the engine has a return line on the rails so any fuel not being used from the fuel pump is instantly sent back into the tank if anything when you get the car dyno tuned you may need a new fuel pump because the stocker may not be able to keep up with the high rpm demands of the 421.
    Quote Originally Posted by Firebirdjones View Post
    Wow, alot is going on here.

    When was the last time 02's were changed? Those need to be changed every 40-50,000 miles. They are a wear item just like spark plugs and are the key factor in trimming fuel. As they get lazy mileage suffers.

    I would also get the car to a dyno tuning facility and get a more accurate tune, especially since we are talking heavily modded and large cubes. I'm sure the mail order tune is working, and it's probably good enough to buzz around and get some easy miles on it. But to really nail it down it needs to be monitored on a chassis dyno, or on the street with a wideband and tuning software.
    There are alot of tuning tricks to gain mileage, but I've found mpg just by fine tuning the AFR with a wideband for a more steady stoich reading. Takes time. Some of those cells jump all over the place and cause the computer to really search around for 14.7, that hurts mileage and throttle response.
    I'm no tuning genius with these computers, but I'm betting you'll find quite a bit left to change in that tune when you get it on the machine.

    Other things affect mileage as you know, the usual tire pressure is a big one, plugs, wires, fuel filter, air filter, dirty MAF etc....but I assume you've been through that with this engine swap.
    Jones brings up another good point are your O2 sensors original because if they are they are probably getting lazy and not giving accurate fuel readings which can also hurt mpgs. I dont think personally thats its one big thing hurting fuel economy but a few little things like the o2 sensors not being up to snuff, and the inaccurate tune. Get the car to a dyno and you will learn a lot about what's going on.

  7. #7
    Veteran 0rion's Avatar
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    throw away the timing tricker and sell the MAF on ebay to some other sucker. I'd do that as a starting point then go from there.

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    sunset orange metallic
    01 trans am

    hey guys,

    thanks for all the replies. hopefully i can answer everyones questions. first let me put out here the list of mods I got so far:

    ENGINE & VALVETRAIN
    LQ9 421 ...4.125 stroker
    MS3 cam 114LSA
    1.75 double roller rocker arms
    LS7 lifters
    PROCOMP heads polished &ported heads

    Combustion chamber 62cc
    Intake Port 235cc
    Exhaust port 82cc
    intake valve 2.02
    exhaust valve 1.60
    PROCOMP DOUBLE SPRINGS
    PROCOMP VALVES
    COMPCAM hitech pushrods 7.400 5/16
    COMPCAM double roller timing chain/sprocket
    MELLING high flow oil pump
    POWERFORCE balancer 90032

    FUEL & IGNITION
    FAST 36 pounder fuel injectors(high impedence)
    HIGH FLOW 255 LPH Fuel pump + hot wire kit
    PROFESSIONAL high volume fuel rails
    MSD wires
    NGK spark plugs TR6

    INDUCTION
    PROFESSIONAL TYPHOON intake manifold 85mm inlet
    PROFESSIONAL throttle body 85mm
    SLP MAF 85mm
    SLP Cold air intake
    VOLANT air lid
    Austin scoop extension(for cold air)
    RAM AIR jet system
    SLP smooth bellow

    EXHAUST
    Long Tube headers

    3'' outlet
    1.75'' inlet
    metal gauge 1/16
    primaries 1 5/8
    3'' off-road Y-PIPE
    NO cats
    80 flowmaster muffler
    3' electrical cut-out
    2 widebands

    COOLING
    160 Thermostat
    High Flow waterpump

    REAR END
    MOTIVE performance 410 gears
    AUBURN differential carrier
    MOSER axles
    T/A Girdle cover

    DRIVELINE
    Spec 1 version 2 Clutch rated 599 torque
    Billet F1 flywheel
    New Slave cylinder

    SUSPENSION
    LUNATI Tubular Subframe weld-in
    ADDCO front & rear anti-roll swaybars
    PROTHANE motor & transmission mounts
    UMI torque arm
    UMI Transmission relocation torque arm mount
    UMI rear & front lower control arms
    UMI rear lower control arm relocation brackets
    UMI upper & lower panhard bars
    UMI driveshaft safety loop
    UMI strut tower brace


    The O2's are brand new and so are the extensions. I did replace the coolant temp sensor aalreay and the check engine light no longer comes on with the computer tuning...On a side note next week I will be taking the car to texas speed for a complete dyno. I am very much looking forward to it as Ive been told the dyno should pinpoint the problem at the least. Hopefully nothing has been fried computer wise.what do you all think?

  9. #9
    Junior Member
    Join Date
    Aug 2011
    Location
    el paso
    Posts
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    sunset orange metallic
    01 trans am

    hey guys,

    thanks for all the replies. hopefully i can answer everyones questions. first let me put out here the list of mods I got so far:

    ENGINE & VALVETRAIN
    LQ9 421 ...4.125 stroker
    MS3 cam 114LSA
    1.75 double roller rocker arms
    LS7 lifters
    PROCOMP heads polished &ported heads

    Combustion chamber 62cc
    Intake Port 235cc
    Exhaust port 82cc
    intake valve 2.02
    exhaust valve 1.60
    PROCOMP DOUBLE SPRINGS
    PROCOMP VALVES
    COMPCAM hitech pushrods 7.400 5/16
    COMPCAM double roller timing chain/sprocket
    MELLING high flow oil pump
    POWERFORCE balancer 90032

    FUEL & IGNITION
    FAST 36 pounder fuel injectors(high impedence)
    HIGH FLOW 255 LPH Fuel pump + hot wire kit
    PROFESSIONAL high volume fuel rails
    MSD wires
    NGK spark plugs TR6

    INDUCTION
    PROFESSIONAL TYPHOON intake manifold 85mm inlet
    PROFESSIONAL throttle body 85mm
    SLP MAF 85mm
    SLP Cold air intake
    VOLANT air lid
    Austin scoop extension(for cold air)
    RAM AIR jet system
    SLP smooth bellow

    EXHAUST
    Long Tube headers

    3'' outlet
    1.75'' inlet
    metal gauge 1/16
    primaries 1 5/8
    3'' off-road Y-PIPE
    NO cats
    80 flowmaster muffler
    3' electrical cut-out
    2 widebands

    COOLING
    160 Thermostat
    High Flow waterpump

    REAR END
    MOTIVE performance 410 gears
    AUBURN differential carrier
    MOSER axles
    T/A Girdle cover

    DRIVELINE
    Spec 1 version 2 Clutch rated 599 torque
    Billet F1 flywheel
    New Slave cylinder

    SUSPENSION
    LUNATI Tubular Subframe weld-in
    ADDCO front & rear anti-roll swaybars
    PROTHANE motor & transmission mounts
    UMI torque arm
    UMI Transmission relocation torque arm mount
    UMI rear & front lower control arms
    UMI rear lower control arm relocation brackets
    UMI upper & lower panhard bars
    UMI driveshaft safety loop
    UMI strut tower brace


    The O2's are brand new and so are the extensions. I did replace the coolant temp sensor aalreay and the check engine light no longer comes on with the computer tuning...On a side note next week I will be taking the car to texas speed for a complete dyno. I am very much looking forward to it as Ive been told the dyno should pinpoint the problem at the least. Hopefully nothing has been fried computer wise.what do you all think?

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