4.1 Intial Timing Question
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HT4100 4.1, 4.5, 4.9 Discussion, 4.1 Intial Timing Question in Cadillac Engine Technical Discussion; I have the TPS adjusted properly, the ISC Motor adjusted properly, and no E codes. When I am in diagnostic ...
  1. #1
    87SDeVille is offline Cadillac Owners Member
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    4.1 Intial Timing Question

    I have the TPS adjusted properly, the ISC Motor adjusted properly, and no E codes. When I am in diagnostic mode it shows 12* advance at idle, I know that you should have 10* advance at idle when in "intial timing" mode. The previous owner said that he took it and had "the timing set" before I got the car, however that was done with a bad TPS and the ISC Motor grossly out of adjustment. Do I need to worry about it or should I check it to make sure? What are ya'lls thoughts on this? 87 Sedan Deville 4.1

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    Sevillian273's Avatar
    Sevillian273 is offline Cadillac Owners Connoisseur
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    Re: 4.1 Intial Timing Question

    You are most likely seeing the computer add 2 degrees to the base timing. Whatever the computer displays includes the 10degrees of base timing. You could always check it at the crank while in 'set timing mode'.

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    drewsdeville is offline Cadillac Owners Master
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    Re: 4.1 Intial Timing Question

    Quote Originally Posted by 87SDeVille View Post
    I have the TPS adjusted properly, the ISC Motor adjusted properly, and no E codes. When I am in diagnostic mode it shows 12* advance at idle, I know that you should have 10* advance at idle when in "intial timing" mode. The previous owner said that he took it and had "the timing set" before I got the car, however that was done with a bad TPS and the ISC Motor grossly out of adjustment. Do I need to worry about it or should I check it to make sure? What are ya'lls thoughts on this? 87 Sedan Deville 4.1
    It wouldn't matter whether the TPS and ISC were bad or not. Initial timing is a static and mechanical adjustment. No engine management or control can alter it (in set timing mode).

  5. #4
    steelybill is offline Cadillac Owners Enthusiast
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    Re: 4.1 Intial Timing Question

    I would be inclined to leave it at the 12 degree setting. These engines need all the help they can get, and the two more degrees wont hurt it any.

  6. #5
    87SDeVille is offline Cadillac Owners Member
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    Re: 4.1 Intial Timing Question

    Thanks for your thoughts on the subject. I will probably go head and check the base timing since the ISC motor was so grossly misadjusted (the car was idiling around 850 RPM), to just to be sure.

  7. #6
    ehall's Avatar
    ehall is offline Cadillac Owners Connoisseur
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    Re: 4.1 Intial Timing Question

    The book says to set it for 10 degrees base, but in some cases the emission sticker under the hood will also say to add 1 or 2 degrees. You can set it wherever you want of course, but 12 degrees should be pretty good. I would not go back down to 10, anyway.

    FWIW, these cars use computer to control the spark timing, but they don't use a cam or crank sensor to determine actual rotation. Instead the base timing is used to used as a way to synchronize the cam to the computer (by rotating the distributor until it agrees with the 10-degree reference), and from there the computer controls the spark relative to the coordinated position. If you set the distributor a little higher, the computer still thinks you have it set for 10. It's a trick to advance the spark for a longer and fuller combustion process that only works because of a lack of sensors.

    Also FWIW, the TPS and ISC don't have anything to do with this process, although there is a lot of interaction between the subsystems at idle so it's possible for problems in one area to show up in another (IE, TPS reading open, causing the computer to advance the spark wrongly).

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