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Cadillac DeVille 1985 to 2005 including:
1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, 2004 N* fuel choices...premium wins in Past Cadillac Vehicle Discussion; Originally Posted by MoistCabbage I know my car quite well. Even of using premium fuel have you a whole 5 ...
  1. #16
    knotgoalie's Avatar
    knotgoalie is offline Cadillac Owners Fanatic
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    Re: 2004 N* fuel choices...premium wins

    Quote Originally Posted by MoistCabbage View Post
    I know my car quite well. Even of using premium fuel have you a whole 5 extra HP, you cannot feel or hear that difference in an engine that makes 275-300 HP. In a '60's beetle, maybe, but not in these cars. The demographic that the cars were designed for is completely irrelevant. Idle is totally and utterly unaffected, and any power difference to small to be noticed.
    Ok, first of all you could not be aware of what I do for a living. I work in tv/motion picture production and have spent decades working with picture cars...all of the traffic and any vehicle shots you see on screen are totally controlled and choreographed. We have to work with everything from rusted out shitboxes to new exotics every day depending upon what the scene calls for.

    I'm currently working on a movie set in the 40s using both civilian and military period vehicles. Deal with 70+ year old vehicles for months at a time when they have to be running/ moving on cue and you realise that your long aquired "instant evaluation" skills can apply to any vehicle be it new, not really new, or old so I'm trusting my experience with my own car...no disrespect intended to you because in the first instance, I know nothing of your technical background my friend and you in turn know nothing of mine. I ask that you not denigrate my suppositions outright until one or the other of us is able to present definitive data re 87v94 octane fuel used in a 2004 Deville DHS...K?


    J.R.

  2. #17
    MoistCabbage's Avatar
    MoistCabbage is offline Cadillac Owners 10000+ Posts
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    What does any of that have to do with anything?

    You're saying your fuel mileage has increased - Fact: You cannot calculate a fuel mileage increase (especially a very small one) by running a tank or two of a different fuel and driving normally. You need to run several tanks of each fuel through the engine, and drive under identical conditions, on identical routes.

    You're saying there's more power - Fact: No human being can do the job of a dynamometer, your occupation does not grant you super sensory abilities. You simply cannot feel a tiny power increase in a powerful engine, especially in a heavy vehicle. The power to weight ratio is hardly affected. That would be like noting acceleration differences in a bicycle after removing the reflectors and skipping breakfast.

    You're saying the car idles better - Fact: Unless there was something very wrong with the 87 octane fuel you were using, there is absolutely no difference in how your engine idles. There is essentially no load, no extra high cylinder temperatures from high RPM operation. Everything is operating exactly as it would with 87 octane. The engine would idle just fine with even lower octane fuel.

    You mentioned premium is "insurance". You should do some reading on the Northstars knock detection system. Nothing bad is happening to your engine by using 87 octane fuel, even when the timing needs to be retarded.

    Like I said, use whatever fuel you'd like, but premium does not "win". There is no disadvantage to using it, there is no real notable advantage to using it. It's only better if it makes you feel warm and fuzzy inside.

  3. #18
    SUPER LAC DEVILLE's Avatar
    SUPER LAC DEVILLE is offline Cadillac Owners Enthusiast
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    Re: 2004 N* fuel choices...premium wins

    Quote Originally Posted by MoistCabbage View Post
    It's only better if it makes you feel warm and fuzzy inside.
    It makes me fell warm and fuzzy inside... wait, wait,

    Nope... thats jus the feeling of broke..... (maniacal laugh) HAHAHAHAHAHA!!!!

  4. #19
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: 2004 N* fuel choices...premium wins

    I see another gas war starting. I've said my piece. I'm out.

  5. #20
    drewsdeville is offline Cadillac Owners Master
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    Re: 2004 N* fuel choices...premium wins

    Quote Originally Posted by MoistCabbage View Post
    What does any of that have to do with anything?

    You're saying your fuel mileage has increased - Fact: You cannot calculate a fuel mileage increase (especially a very small one) by running a tank or two of a different fuel and driving normally. You need to run several tanks of each fuel through the engine, and drive under identical conditions, on identical routes.

    You're saying there's more power - Fact: No human being can do the job of a dynamometer, your occupation does not grant you super sensory abilities. You simply cannot feel a tiny power increase in a powerful engine, especially in a heavy vehicle. The power to weight ratio is hardly affected. That would be like noting acceleration differences in a bicycle after removing the reflectors and skipping breakfast.

    You're saying the car idles better - Fact: Unless there was something very wrong with the 87 octane fuel you were using, there is absolutely no difference in how your engine idles. There is essentially no load, no extra high cylinder temperatures from high RPM operation. Everything is operating exactly as it would with 87 octane. The engine would idle just fine with even lower octane fuel.

    You mentioned premium is "insurance". You should do some reading on the Northstars knock detection system. Nothing bad is happening to your engine by using 87 octane fuel, even when the timing needs to be retarded.

    Like I said, use whatever fuel you'd like, but premium does not "win". There is no disadvantage to using it, there is no real notable advantage to using it. It's only better if it makes you feel warm and fuzzy inside.
    Fact: your 'fueling' the eternal fire. What are you accomplishing here? He likes his premium fuel. Let it go.

  6. #21
    MoistCabbage's Avatar
    MoistCabbage is offline Cadillac Owners 10000+ Posts
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    As I posted, he should use whatever he likes, it's his car.

  7. #22
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    Re: 2004 N* fuel choices...premium wins

    Update...data bs on the premium, so far. To a degree the "butt dyno" has been correct but not for the right reasons. I committed the ultimate dumb of evaluation by switching fuel grades to premium after giving the previous tank of regular a mild overdose of Lucas injector cleaner/upper cyl. lube. Who knows if or when it had been done before? I very much suspect that the smoother idle and pretty song @ wot are far more attributable to the cleaner than to the higher octane gas so I retract my previous follies and fuel on 87 heretofore. Should I however decide at whatever time to do a late night superhighway/between major cities "how fast will this barge go" kind of run...I'll run it low and then fill with premium just to be sure


    J.R.

  8. #23
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    Re: 2004 N* fuel choices...premium wins

    For the 2004, does your owner's manual say something like "Use regular unleaded gasoline with a posted octane of 87 or higher. However, for mountain driving, trailer towing, or maximum performance operation you may want to use a premium fuel".

    That's a generic statement from the 2000 and later Northstar manuals - the 2000-2004 engines had a 10.0:1 compression ratio, slightly different spark plug location, and timing set to use 87 octane fuels. (Ignition timing will NOT advance past the preset specs in response to using premium fuels.) Maximum advance in these engines is 35° BTDC, and at 60+mph road speeds the timing hovers around 31° - 34° BTDC. Touch the gas pedal to pass or rapidly accelerate and timing instantly drops back to 18° - 25° BTDC, regardless of fuel used. At WOT, 130 mph in 3rd gear (STS) the timing is about 20° BTDC.

    For someone who likes to monitor their engine functions, take a look at a ScanGauge-II. www.scangauge.com

  9. #24
    basscatt's Avatar
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    Re: 2004 N* fuel choices...premium wins

    Quote Originally Posted by knotgoalie View Post
    Update...data bs on the premium, so far. To a degree the "butt dyno" has been correct but not for the right reasons. I committed the ultimate dumb of evaluation by switching fuel grades to premium after giving the previous tank of regular a mild overdose of Lucas injector cleaner/upper cyl. lube. Who knows if or when it had been done before? I very much suspect that the smoother idle and pretty song @ wot are far more attributable to the cleaner than to the higher octane gas so I retract my previous follies and fuel on 87 heretofore. Should I however decide at whatever time to do a late night superhighway/between major cities "how fast will this barge go" kind of run...I'll run it low and then fill with premium just to be sure


    J.R.
    -----------------------------
    "how fast will this barge go"
    it will ZOOM right up to 112 MPH - then the fuel injectors will shut down -

    once your speed falls below 112 - the injectors will become activated again -

    speed limiters were set according to the type of tires it received at the factory -

    L 75 mph 120 km/h Off-Road & Light Truck Tires
    M 81 mph 130 km/h Temporary Spare Tires
    N 87 mph 140km/h
    P 93 mph 150 km/h
    Q 99 mph 160 km/h Studless & Studdable Winter Tires
    R 106 mph 170 km/h H.D. Light Truck Tires
    S 112 mph 180 km/h Family Sedans & Vans
    T 118 mph 190 km/h Family Sedans & Vans
    U 124 mph 200 km/h
    H 130 mph 210 km/h Sport Sedans & Coupes
    V 149 mph 240 km/h Sport Sedans, Coupes & Sports Cars
    W 168 mph 270 km/h Exotic Sports Cars
    Y 186 mph 300 km/h Exotic Sports Cars


    base Deville and DHS models got "S" rated tires -
    the DTS normally got "H" tires -
    a few - VERY FEW" - got "Z" rated tires -

    THERE WERE A FEW EXCEPTIONS -
    for instance - in 2002 - there were 33 DHS models -
    that were ordered with the RPO code "QNI" - 225/60/16 "Z" rated tires -

    just FYI - Seville SLS models also got "S" tires -
    and MOST Seville STS models got "H" tires -
    and a few got "Z" tires -

  10. #25
    maxjeepster83 is offline Cadillac Owners Member
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    Re: 2004 N* fuel choices...premium wins

    when i first bought my 04 Deville i was using 87 octane but it would knock when going up hill, i read the owners manual & it said u could use the 92 if it does that, so i kept using the 92 octane fuel & it clogged my convertor & i had to replace it, so now i stick to 87 octane with no problems & no expense of a $1400 exhust bill.......LOL

  11. #26
    Submariner409's Avatar
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    Re: 2004 N* fuel choices...premium wins

    Post #24 is correct ---- and the speed rating for your car is printed on the tire specs sticker on the driver's door edge.

    maxjeepster, Using premium fuels in your engine had exactly nothing to do with "clogging my converter". The knocking when going up hills or on mild acceleration was probably caused by partially clogged EGR passages. As a matter of fact, 89 and 91/93 octane gasoline burns slower than 87 in order to control flame travel at high power demands.

    There are simply too many 2000 - 2004 Seville/Deville drivers in here who use 91/93 octane fuels almost exclusively, with NO problems, to support the theory that running higher octane fuels can damage a catalytic converter.

    EDIT: Please Google "top tier gasoline" and do some studying.

  12. #27
    Ranger's Avatar
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    Re: 2004 N* fuel choices...premium wins

    Quote Originally Posted by maxjeepster83 View Post
    i kept using the 92 octane fuel & it clogged my convertor
    That is ridiculous. You may have had a clogged CAT, but I can guarantee you it was NOT caused by higher octane.

    i was using 87 octane but it would knock when going up hill
    More likely a bad EGR valve than octane related.

  13. #28
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    Re: 2004 N* fuel choices...premium wins

    Sub and Ranger are dead on. Both accurate. cannot have cause a cat failure, and sub has listed the correct data.
    RX Performance Products/RevXtreme.com 941-721-1826

  14. #29
    SUPER LAC DEVILLE's Avatar
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    Re: 2004 N* fuel choices...premium wins

    Quote Originally Posted by Ranger View Post
    More likely a bad EGR valve than octane related.
    "bad EGR valve".... if knock is the clacking noise when i step on the gas... can i fix/replace it... wheres it at?????????

  15. #30
    BlackInjun is offline Cadillac Owners Member
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    Re: 2004 N* fuel choices...premium wins

    Quote Originally Posted by MoistCabbage View Post
    As I posted, he should use whatever he likes, it's his car.
    I think Moist is absolutely correct here (meaning all his posts). In fact I think everyone here should realize that moistsubbass.... nevermind I can't remember, but I do know I get better gas mileage and more power when I put gas in the car. Also more importantly it's 60 degrees outside in DC.

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