Spark Plug Change
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  • 1 Post By KRSTS
Cadillac STS Forum - 2005 through 2012 Discussion, Spark Plug Change in Past Cadillac Vehicle Discussion; About a month ago I had misfire on cylinder #2. I replaced the coil and while I was at it ...
  1. #1
    KRSTS is online now Cadillac Owners Enthusiast
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    Spark Plug Change

    About a month ago I had misfire on cylinder #2. I replaced the coil and while I was at it decided to replace my spark plugs also. I have the 3.6L V6 DI engine so I did not have to remove the intake plenum. Very easy job. I replaced them with OEM Delco platinum. The old plugs looked OK, but the gap was way wide. My car has 61000 miles. I have been monitoring my fuel use very closely since then and my combined mileage has gone from 17.8 MPG to around 19 MPG. No changes in my driving habits or anything else. Seems like new plugs made quite a difference. I always use top tier gas and an occasional bottle of Techron. Just thought I'd pass this along.
    Subsailor613 likes this.

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  3. #2
    Chinny is offline Cadillac Owners Member
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    Thanks for the input, have 76000 on mine and noticed some power loss/engine hesitation at higher rpms. Some research seems to suggest changing the plugs as a start. Alreadt bought the AC Delco plugs just have to change em. Ill monitor the mpgs after too, if i get more thats a bonus.

  4. #3
    AQJ
    AQJ is offline Cadillac Owners Member
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    Re: Spark Plug Change

    KRSTS,

    I have a misfire on cylinder #4 of my 09' STS. Replacing the coil seems fairly simple, but how do I determine where the #4 cylinder is?

  5. #4
    Ludacrisvp's Avatar
    Ludacrisvp is offline Cadillac Owners Connoisseur
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    Re: Spark Plug Change

    Quote Originally Posted by AQJ View Post
    KRSTS, I have a misfire on cylinder #4 of my 09' STS. Replacing the coil seems fairly simple, but how do I determine where the #4 cylinder is?
    What engine do you have?
    V6 -or- V8

  6. #5
    daddy_o's Avatar
    daddy_o is offline Cadillac Owners Fanatic
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    Re: Spark Plug Change

    Quote Originally Posted by KRSTS View Post
    About a month ago I had misfire on cylinder #2. I replaced the coil and while I was at it decided to replace my spark plugs also. I have the 3.6L V6 DI engine so I did not have to remove the intake plenum. Very easy job. I replaced them with OEM Delco platinum. The old plugs looked OK, but the gap was way wide. My car has 61000 miles. I have been monitoring my fuel use very closely since then and my combined mileage has gone from 17.8 MPG to around 19 MPG. No changes in my driving habits or anything else. Seems like new plugs made quite a difference. I always use top tier gas and an occasional bottle of Techron. Just thought I'd pass this along.
    Interesting that after 61K that the gap has widened, do you have a measurement number?
    I am on the understanding that these platinum plugs are good for 100,000.
    Not to start trouble, but, what octane gas do you use?
    And what does the manual say for octane?

    My 07 CTS 3.6 required 89 octane, by the manual. I would lose 2 mpg if I used 87 octane.
    But my 10 STS 3.6 requires only 87 octane, by the manual. I saw no gain by using 89.

  7. #6
    CadiTamer is offline Cadillac Owners Fanatic
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    Re: Spark Plug Change

    My 2006 3.6 STS was getting about 14MPG (i drive nearly 100% city, and it's hard city driving too), and is closer to 17 now that i changed the plugs. Was at 131K when i changed them, and the gap had gotten pretty wide... They were dry, except some oil that had leaked down the spark plug tube on cylinder #5.

  8. #7
    KRSTS is online now Cadillac Owners Enthusiast
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    Re: Spark Plug Change

    Quote Originally Posted by daddy_o View Post
    Interesting that after 61K that the gap has widened, do you have a measurement number?
    I am on the understanding that these platinum plugs are good for 100,000.
    Not to start trouble, but, what octane gas do you use?
    And what does the manual say for octane?
    Spec gap is .043 for ACDELCO Platinun Professional #41-990. The ones I took out were at .058 but otherwise normal in every way. I just looked at the box and it says 100,000 Mile limited warranty against defects in design, materials and workmanship. Nothing about longevity. I use Top Tier 87 octane just as the manual recommends, usually Exxon or Shell. Hope this answers your questions daddy_o.

  9. #8
    funk_drum is offline Cadillac Owners Member
    Automobile(s): 2008 STS4
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    Re: Spark Plug Change

    I think the 100,000 mile thing is for the electrode. Not sure how the gap would stay the same over that many miles.

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