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Cadillac Seville / Cadillac Eldorado Forum Discussion, Major malfunctions 99 STS in Past Cadillac Vehicle Discussion; If you have no spark at the plugs, I'd suspect the ICM. Check the 4 connectors (2 on each side ...
  1. #16
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: Major malfunctions 99 STS

    If you have no spark at the plugs, I'd suspect the ICM. Check the 4 connectors (2 on each side of it).

  2. #17
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    divine97godly is offline Cadillac Owners Member
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    Charged the battery got it running but it was so rough too rough to drive it was reviving up and eventually cut itself off the engine also has a loose PCv valve. Which hose was cracked right at the vavle and it wasnt very secure into the engine assembly

  3. #18
    the recluse is offline Cadillac Owners Connoisseur
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    Re: Major malfunctions 99 STS

    if the motor was revving up and running rough, you may have a vacuum leak, or maybe a torn plenum? Others will have to back up that diagnosis, as I'm not sure if that year has a plenum or not...

  4. #19
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    Re: Major malfunctions 99 STS

    No plenum on his '99. That's on the 2000+ engines.

    Fix the loose PCV. That's your vacuum leak.

  5. #20
    mike5514 is offline Cadillac Owners Enthusiast
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    Re: Major malfunctions 99 STS

    Yup a bad pcv valve will make a engine run like crap learned the hard way.Mike

  6. #21
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    divine97godly is offline Cadillac Owners Member
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    Fixed the PCv valve, still couldn't get my car to start just cranking so another AAA tow to the shop that replaced the plugs last week along with the fpr! Hopefully they can tell me some type of idea about what's going on appreciate all the insight, as soon as I hear back I'll post it.

  7. #22
    mike5514 is offline Cadillac Owners Enthusiast
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    Re: Major malfunctions 99 STS

    Sounds more and more like VATS. Mike

  8. #23
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    MoistCabbage is online now Cadillac Owners 10000+ Posts
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    It's not VATS if it's cranking.

  9. #24
    mike5514 is offline Cadillac Owners Enthusiast
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    Re: Major malfunctions 99 STS

    Moist I thought VATS cranked but no fuel? Mike

  10. #25
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    Re: Major malfunctions 99 STS

    No, it also disables the start enable relay.

    System Operation

    When the system is operating in normal mode, the VATS decoder reads the correct resistance during cranking. The module grounds the Start Enable Relay coil. When the start enable relay contacts close, voltage is allowed to the "S" terminal of the starter. The VATS module also sends an enable signal to the ECM. This signal allows the ECM to operate the fuel injectors during cranking. The SECURITY light will also illuminate for approximately five seconds, then turn off and remain off.

    If an incorrect or no key resistance is read by the VATS decoder module, the module will shut down the start enable and ECM signal outputs for 4 minutes. The SECURITY light will flash during the cranking attempt, and will remain on during the 4-minute duration. Even if the correct resistance is read within that 4 minute duration, the VATS module will not operate the relay or signal the ECM..An error code.53 will also be set if the proper signal is not being received on CKT 229 by the ECM when the ignition is turned ON.

  11. #26
    jcresciSTS is offline Cadillac Owners Enthusiast
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    Re: Major malfunctions 99 STS

    Make sure they use AC Delco Platinum 41-950 spark plugs.

  12. #27
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    divine97godly is offline Cadillac Owners Member
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    Well they used r and r spark plugs!! Which I never heard of so I guess they are generic brand plugs, haven't heard back from that shop yet!! I just wanted a diagnostic of the problem, which I'm thinking the plugs need to be replace again.

  13. #28
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    Submariner409 is offline If it won't run, chrome it
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    Re: Major malfunctions 99 STS

    There's no "think" involved: Use the correct spark plugs - the cutesy " R & R Plugs" are nothing more than a cash cow for the shop.

    (........ by the way........... "R & R" in labor lingo means "Remove and Replace". It is used to add in extra labor time.)

  14. #29
    jcresciSTS is offline Cadillac Owners Enthusiast
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    Re: Major malfunctions 99 STS

    I missed the R&R plugs part but yeah def get them changed to the Delco's.

    12.5 running? That's really low. FWIW when my alt in my 99 went on me every light in the car came up along with all the "service" messages

  15. #30
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    divine97godly is offline Cadillac Owners Member
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    12.5 reading without it running. My battery was 35% charged according to the autozone reading.

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