Slightly Erratic Ignition Timing

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Cadillac DeVille 1985 to 2005 including:
1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, Slightly Erratic Ignition Timing in Past Cadillac Vehicle Discussion; Hi guys. Question about timing. Long time ago when I hooked up a vac pressure gage, the vac at idle ...
  1. #1
    Piterrr is offline Cadillac Owners Member
    Automobile(s): 1992 De Ville Sedan
    Join Date
    Oct 2013

    Slightly Erratic Ignition Timing

    Hi guys.

    Question about timing.

    Long time ago when I hooked up a vac pressure gage, the vac at idle would generally hold steady at 18 inHg and very slowly fluctuate between 17..19 inHg. After doing extensive googling, I found the probable cause was likely a problem with ignition timing. Indeed, when I put the PCM in timing mode by jumping the ALDL connector, the base timing is supposed to be 10 deg before TDC, but the timing mark on the pulley actually oscillated between 12...8 deg, which would explain the vac gage fluctuation. This has been going on for years now and I would like to fix this if possible. What would be causing this? Timing belt too long? Distributor shaft gear worn out? Anything wrong with the distributor itself? What would be the most likely suspect to look at first?

    The car has 210k miles on it, 92 deville, 4.9 motor.
    Any input appreciated.


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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: Slightly Erratic Ignition Timing

    Distributor gear, timing chain/sprockets, (?) distributor advance flyweight spring(s).

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