'91 Deville, a few questions
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  • 4 Post By Faith76
Cadillac DeVille 1985 to 2005 including:
1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, '91 Deville, a few questions in Past Cadillac Vehicle Discussion; Greetings. I'm new to the forums. I don't know what kind of modifying you guys do, but that's a bit ...
  1. #1
    Beuks is offline Cadillac Owners Member
    Automobile(s): 91 Sedan Deville
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    '91 Deville, a few questions

    Greetings. I'm new to the forums. I don't know what kind of modifying you guys do, but that's a bit of what I'm looking for.

    Now, I've got a couple questions. First off, I've got a '91 Sedan DeVille with 183k miles on it. The engine still runs like a champ, but it idles a little rough. It doesn't just sit there and purr. It surges a little. The variance is maybe 100 RPM, so nothing huge, but I'm wondering if this is normal with old age or if I should worry. It also does it worse (~100 RPM, maybe worse) when I press the throttle lightly and rev it ~1k RPM and hold.

    Second, I'm wondering about transmission swaps. I understand that the stock 4T60-E is strong, but mine is getting up there (original trans. as far as I know) and I'd like something with better gearing (I want lower revs at cruising speeds), in a manual transmission if I can. My biggest concern with the manual transmissions, though: The ones I know of were all behind smaller, less powerful engines, so I'm concerned with reliability, especially in this car because it's bigger than anything these transmissions were ever in. I'm also concerned with how exactly the computer would react if there suddenly weren't a transmission controller for it to communicate with. Would it throw codes, would it retard the performance of the engine, etc.

    Third, I would really like to know about the aftermarket upgrades for this car. I've heard of next to nothing that can be done with these engines, aside from a K&N drop in filter, an Allante intake, and catless higher-flow exhaust. Mine currently has the K&N drop in, and a stock muffler modified for dual 3-inch outlet with stainless angle-cut tips. Where can I go (online) to buy aftermarket upgrades, and what can be repurposed from other engines to improve this one? Also, I don't actually remember what kind of improvement I can expect from the Allante intake.

    Thanks for whatever input you can offer. Direct me where you can.

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  3. #2
    MoistCabbage's Avatar
    MoistCabbage is online now Cadillac Owners 10000+ Posts
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    Most members here aren't into modifications, which is just as well, because there is NO aftermarket support for these cars, brake pads and tires, thats's IT.

    Your car already has a CAI that flows more air than the engine can use at WOT, at redline. And FWIW, K&N filters don't make any measurable difference, flow more dirt, and pack up 3 times as fast.

    Exhaust mods will get you sound, but no more than one or two more HP.

    If there was a manual transmission that would work with the 4.9, and bolt into the car, the car electronics would not be happy. And what would you use for seats, a console, shifter and linkage?

    These are the WRONG cars for tuners.

    As for the surging, is it surging up and down, or could you call it a stumble?

  4. #3
    cadillac_al is offline Cadillac Owners Connoisseur
    Automobile(s): Cadillac 78 Seville, 78 Coupe de Ville, 92 Sedan de Ville
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    Re: '91 Deville, a few questions

    You forgot to mention when it was tuned up last. I would run some Techron in the gas for starters.

  5. #4
    Faith76's Avatar
    Faith76 is offline Cadillac Owners Enthusiast
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    Re: '91 Deville, a few questions

    I just don't understand why you'd want to make a Cadillac loud.

  6. #5
    basscatt's Avatar
    basscatt is online now Cadillac Owners 10000+ Posts
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    Re: '91 Deville, a few questions

    Quote Originally Posted by Beuks View Post
    Greetings. I'm new to the forums. I don't know what kind of modifying you guys do, but that's a bit of what I'm looking for.

    Now, I've got a couple questions. First off, I've got a '91 Sedan DeVille with 183k miles on it. The engine still runs like a champ, but it idles a little rough. It doesn't just sit there and purr. It surges a little. The variance is maybe 100 RPM, so nothing huge, but I'm wondering if this is normal with old age or if I should worry. It also does it worse (~100 RPM, maybe worse) when I press the throttle lightly and rev it ~1k RPM and hold.

    Second, I'm wondering about transmission swaps. I understand that the stock 4T60-E is strong, but mine is getting up there (original trans. as far as I know) and I'd like something with better gearing (I want lower revs at cruising speeds), in a manual transmission if I can. My biggest concern with the manual transmissions, though: The ones I know of were all behind smaller, less powerful engines, so I'm concerned with reliability, especially in this car because it's bigger than anything these transmissions were ever in. I'm also concerned with how exactly the computer would react if there suddenly weren't a transmission controller for it to communicate with. Would it throw codes, would it retard the performance of the engine, etc.

    Third, I would really like to know about the aftermarket upgrades for this car. I've heard of next to nothing that can be done with these engines, aside from a K&N drop in filter, an Allante intake, and catless higher-flow exhaust. Mine currently has the K&N drop in, and a stock muffler modified for dual 3-inch outlet with stainless angle-cut tips. Where can I go (online) to buy aftermarket upgrades, and what can be repurposed from other engines to improve this one? Also, I don't actually remember what kind of improvement I can expect from the Allante intake.

    Thanks for whatever input you can offer. Direct me where you can.
    --------------------------------
    The engine still runs like a champ, but it idles a little rough
    check for Diagnostic Trouble Codes -

    if you don't know how - go here and read the ENTIRE post -

    http://www.cadillacforums.com/forums...odes-dtcs.html

    if you have any codes - post them here -
    ALONG WITH THEIR DEFINITIONS -
    ---------------------------------

    clean the throttle body - make sure the egr tubes are clear -

    -----------------------
    I'm wondering about transmission swaps
    no other trans is available -

    ------------------
    I would really like to know about the aftermarket upgrades for this car.
    that's an easy one to answer -

    there are none - nada - ZERO - ZILCH -

    Mine currently has the K&N drop in,
    pleated paper filters are actually better at trapping dirt -
    and a regular paper filter will flow more air
    than the engine can suck at full throttle - at redline -

    a stock muffler modified for dual 3-inch outlet
    with stainless angle-cut tips.

    pure bling - zero gain in power or mileage -

    Where can I go (online) to buy aftermarket upgrades,
    no where - because there is nothing to buy -


    what can be repurposed from other engines to improve this one?
    nothing - absolutely nothing -

    what kind of improvement I can expect from the Allante intake
    nothing -

    Direct me where you can.
    you bought the wrong car for modding -

    BLING - like wheels and tires -

    better brake pads and rotors -

    and that's about it -

  7. #6
    dommi.b is offline Cadillac Owners Member
    Automobile(s): 1995 Deville Base 4.9L
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    Re: '91 Deville, a few questions

    I agree, a quiet ride is what you'd want in a luxuy car like the deville... but boy do these 4.9L's sound good with straight pipes!

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