Spark advance/knock - What is tolerance?

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Northstar Engines and System Technical Discussion Discussion, Spark advance/knock - What is tolerance? in Cadillac Engine Discussion; I am aware of what a knock sensor does, what the spark advance is and how they relate to the ...
  1. #1
    TryMe96Z is offline Cadillac Owners Member
    Automobile(s): 1996 STS (220K+)
    Join Date
    Jul 2004

    Spark advance/knock - What is tolerance?

    I am aware of what a knock sensor does, what the spark advance is and how they relate to the performance of the engine. But what I cannot seem to find it was the acceptable min/max values are. I am seeing upwards of -40 degrees of spark advance when at 1700 rpm. Based off what I know the spark advance should not be getting this high should it? I cannot say that there is anything running poorly about the car other than it really believes it needs a new catalytic converter (p0420. Cat is not causing back pressure, and o2 sensors are responding correctly).

    If there are other supporting metrics I need to post let me know, I have an OBDII monitoring software that provides a lot of the key metrics.


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  3. #2
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
    Automobile(s): 2002.5 F55 STS - 67,500 miles, 2014 Explorer XLT FWD
    Join Date
    Feb 2006
    MD Eastern Shore, Kent Island

    Re: Spark advance/knock - What is tolerance?

    All depends on your car, year, model, engine. Update your profile.

    Monitoring my 2002.5 STS ignition I see anywhere from 4 degrees BTDC to 36 degrees BTDC, depending on road, load, power demand, throttle opening, etc, etc. If you monitor the OBD port you know that timing on these engines is extremely dynamic - it never stays at one setting for long - even a gust of wind changes timing - due to load - in these cars.

    Probably nothing wrong with 40 degrees BTDC on a light load, moderate speed gentle steady drive - but touch the pedal to keep speed on a slight incline and timing drops back - sometimes radically. You'll never be able to break out the knock sensor contribution - it's too small a contribution and usually NEVER comes into play except under maximum power demand operation - WOT ...... and then timing is radically retarded anyway - in any ignition setup.........

    EDIT: When running down the highway at 60 cruise, my ignition advance hovers at about 30 - 34 degrees BTDC. Punch it to pass a car and timing instantly retards to 16 - 24 degrees BTDC......... get off the pedal and timing goes right back to 30 -33. Above 65, timing begins to gradually retard from 33 as wind drag increases needed power. At a steady 100 mph the timing sits at 24 - 26 degrees BTDC. Normal. (and, FWIW, it makes absolutely NO difference whether I run 87 or 93 octane. Tried it all under many varying conditions.)

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