Replacing Spark Plugs
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5.0 and 5.7 Discussion, Replacing Spark Plugs in Cadillac Engine Technical Discussion; The 93 Fleetwood started running a little rough earlier this week - idle became rough, not as much power as ...
  1. #1
    jey
    jey is offline Cadillac Owners Fanatic
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    Replacing Spark Plugs

    The 93 Fleetwood started running a little rough earlier this week - idle became rough, not as much power as usual, etc. It was a regular throb that varied exactly with the speed of the engine. I figured I was missing a cylinder or something - definitely an ignition problem - it was too regular/consistent to be fuel delivery on a TBI car.

    I have recently changed the distributor cap, rotor, and plug wires, so it was time to go after the plugs themselves. Had to wait a day for Advance Auto to order in AC Delco platinum plugs (OEM replacement), but at least they could do it (Autozone couldn't get them).

    Was worried I couldn't get it done this weekend due to a big cold front and then the remnants of hurricane Ike, but Saturday turned out to be a great day, so I got under there and changed them all out.

    Here are the old plugs - cylinders 7, 5, 3, 1 and top and 8 through 2 on bottom:



    Looks like cylinder 8 was my problem. Car runs smooth now!

    Next on the list is a coolant flush - it's looking a little dirty in the overflow reservoir.

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  3. #2
    carnut is offline Cadillac Owners Master
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    Re: Replacing Spark Plugs

    Looks like #8 is pushing a little oil thru the valve guide seal.

  4. #3
    jey
    jey is offline Cadillac Owners Fanatic
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    Re: Replacing Spark Plugs

    Yeah - it's not consuming any oil that I can tell. I wonder if the amount of oil getting through is a problem, and if there is anything I should worry about / address in the near future.

    The next maintenance item on my list is the coolant flush - dang this thing takes a ton of coolant (14-16 quarts!). I'll have to pick up a few jugs of distilled water on my next trip to the parts store, and get some of those supplement pellets too.

  5. #4
    Slacker is offline Cadillac Owners Fanatic
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    Re: Replacing Spark Plugs

    I'd say that if the leak continues, it'll just foul up the new plug eventually and you'll be hit with the same problem down the road. You can push it off, but it'll one day need to be addressed.

    Also, if the engine is an Olds 307 or a Chevy 305/350, to my knowledge you shouldn't need the pellets. I thought that was only for the HT4100-4500-4900 engines...

  6. #5
    jey
    jey is offline Cadillac Owners Fanatic
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    Re: Replacing Spark Plugs

    Quote Originally Posted by Slacker View Post
    Also, if the engine is an Olds 307 or a Chevy 305/350, to my knowledge you shouldn't need the pellets. I thought that was only for the HT4100-4500-4900 engines...
    It was in the Factory Service Manual so I put one pellet in there. Didn't do a full system flush since the fluid looked good (it was just the overflow tank that was nasty).

  7. #6
    carnut is offline Cadillac Owners Master
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    Re: Replacing Spark Plugs

    Antifreeze becomes corrosive over time regardless of color. 2 year interval changes are recommended to keep this from occuring. The use of the sealant pellets is recommended especially on the Olds engine. They had a tendency to corrode the aluminum intake where it joins the cast iron cyl. head at the front or rear corners because of late antifreeze replacement

  8. #7
    jey
    jey is offline Cadillac Owners Fanatic
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    Re: Replacing Spark Plugs

    Yeah all I did was drain the radiator/overflow and refill essentially. I started to find the knock sensor and block plug to do a full system drain/refill but got lazy. I figure the radiator flush is enough preventative maintenance for now, though I've heard people theorize that if you just do that every year it's almost as good as doing a block drain/refill every 2 years.

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