Hummmm? Fuel drop after...
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  • 1 Post By silversport
Cadillac SRX First Generation Forum - 2004 - 2009 Discussion, Hummmm? Fuel drop after... in Cadillac SRX Forums; Hi all! Quick recap... 2008 SRX, AWD, 3.6, /W SPORT PACAKAGE (what ever that means) Cut the resonator off and ...
  1. #1
    amcon's Avatar
    amcon is offline Cadillac Owners Member
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    Hummmm? Fuel drop after...

    Hi all!

    Quick recap... 2008 SRX, AWD, 3.6, /W SPORT PACAKAGE (what ever that means)

    Cut the resonator off and straight piped it... (great sound and gained about 1.5 mph-instantly) just added and aftermarket air intake box, with k&n filter - goal was to increase cool air flow, all seems good it was a solid fit and all.

    Good parts - "seems" as if I have increased performance again. However, just under heavy exceleration.

    Bad parts - I have lost about 3mph!!! (actually 2.8 mph - documented after two tank full of gas) ( ote: I get gas from same place, same pump)

    So here is my question :

    Why would increased airflow lower gas milage?

    Possible solutions?

    -pull battery and reset computer?

    Help help...

    ----------

    Help... Lol

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  3. #2
    SFVetteman's Avatar
    SFVetteman is offline Cadillac Owners Fanatic
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    Re: Hummmm? Fuel drop after...

    The computer tries to maintain an air/fuel ratio of around 13/1. Increased air flow results in the computer adding fuel to maintain the ratio. Cooler air is more dense and therefore contains more oxygen. The computer sees the lower temperature and responds by adding fuel.

    You got your performance increase but it doesn't come out of thin air.

    Bill

  4. #3
    amcon's Avatar
    amcon is offline Cadillac Owners Member
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    Re: Hummmm? Fuel drop after...

    Bill you rock... Yea, just jumped out of the car, and I Def feel the performance, but it's at least 3 gallons less! Om gosh.

    Any computer adjustments I can do? Programmer??...? Chip?

  5. #4
    SFVetteman's Avatar
    SFVetteman is offline Cadillac Owners Fanatic
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    Re: Hummmm? Fuel drop after...

    You can minimize the fuel loss by economizing your driving style; in other words if you don't use the new found power then you don't have to pay for it. A good tune might well help recover a lot of the fuel loss, if you do a lot of freeway driving, as most cars come from the factory with a conservative tune that is on the rich side (more fuel) and ignition timing that is less than optimum. A mail order tune is an option to obtain a close to optimum tune although a custom tune on a load bearing dyno that is done locally is better but likely considerably more expensive. Bottom line is that conservative driving is the best way to maximize the mpg. A good tune may help but the payback is way down the road due to the cost of the tune.

    Bill

  6. #5
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    Re: Hummmm? Fuel drop after...

    ...and I always found that the louder the sound...the more I couldn't keep my foot out of it... ...

    Bill
    amcon likes this.

  7. #6
    The Wrench is offline Cadillac Owners Enthusiast
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    Re: Hummmm? Fuel drop after...

    The ECM has the ability to control the air/fuel ratio very closely, as long as the system hasn't been modified enough to skew the fuel trims by more than 10% or so. So, theoretically, making minor changes to intake and exhaust should be easily handled by the computer, at least at part throttle (99.5% of our driving).
    But......... this system depends on very accurate readings from the mass air flow sensor in the intake, and the O2 sensor in the exhaust. If either system is modified to the point that the airflow around the sensor is changed, then an erroneous reading could easily occur. We saw it all the time on the Vettes when we changed air filter setups: the qty of air flow at part throttle was not the culprit - it stayed the same, as the engine could easily pull what it needed at low volume demands, even thru a badly clogged stock unit.
    But, with a modified intake, the turbulance of the air past the sensor changed, and even at 1/10th throttle, the sensor misread the air volume and mis-set the AF ratio. The O2 sensor could adjust it back via the fuel trims if it wasn't off enough, but the computer had issues trying to reset the full-throttle ratio based on what it last saw at part-throttle. As for the O2 sensor, it is just as sensitive to flow changes as the mass air sensor. Removing restriction in the system can definitely affect the flow pattern at the sensor, even though it's ahead of the cats, and the O2 sensor will not achieve correct readings.

    All that said, first check might be to hook up a scanner and check fuel trims at various throttle settings. if they are off Zero more than 10%, then a dyno tune might be beneficial. Actually, a good tune could add some noticeable response and punch to the engine, maybe 10-15 HP.
    Of course the real issue might be your right foot, as stated above!!!!!! I can easily vary MPG over a tankful by 20%, just by changing driving habits a bit.

    DG

  8. #7
    amcon's Avatar
    amcon is offline Cadillac Owners Member
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    Re: Hummmm? Fuel drop after...

    I will look locally for someone who can "tune" the srx... Interesting... And for a heavy car, all wheel drive (or the equivalent) I'm impressed with the throttle response... And the additional sound is very pleasing as I sport shit into the 4k range....:-)

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