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1992 Cadillac Sedan DeVille 4.9L (Deceased), 1991 Cadillac Sedan DeVille 4.9L
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105 Posts
Discussion Starter #1
I've read on here and in the FSM how to jump the ALDL, loosen the dist., and change the timing using the timing light. However, I also saw in the manual that you can go into the diagnostics mode 5.9 (Let it read 7.0, hit HI, it'll read 9.5, than hit ECON and WARMER, it'll read 5.0, then LO or HI a few times to get to 5.9), which also reads the timing and say you can even set it within a couple degrees of 10. Just curious how the methods compare? If I want it on 12, can I set it with the computer?

Also, for fun, I hooked up my timing light without the ALDL or anything and it was reading ~12 (Bounced between 11-13, not sure why it's not steady). Then, I entered diagnostic mode 5.9, which reads the timing, and it was reading around 20 on the display. Why is there a discrepancy?
 

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92 Fleetwood 2dr cpe - FWD, 96 Seville SLS, 02 Seville
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1,007 Posts
5.9 is a temporary spark advance setting. On leaving diagnostics, the setting will return to normal.

You want to read actual spark advance using 0.6 (enter LO after 7.0, then scroll)

Now the interesting FSM writeup
  • normal method to set timing requires jumping the ALDL with car off and not in diagnostics. Start car and adjust.
  • FSM hidden: the 5.9 writeup has 2 stages. The first stage is the initial reading went scrolling to 5.9. When you select COOLER here, it will put the PCM into SET TIMING MODE and show 10. You can adjust the distributor at this point using your timing light to achieve 10 (matching what the FDC shows). Lock distributor down. Any further pressing of COOLER or WARMER will be the second stage of 5.9. These will adjust timing temporary advice and below 10. There are limits on the PCM for range of advance per rpm. Set it too high and it will refuse. Raise your rpm's and you'll find that the boundary of the manual advance will change as well.

And yes, Under normal operation, the timing will bounce around as the computer constantly adjusts AFM resulting in rpm changes that require spark advancement changes.
 

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1992 Cadillac Sedan DeVille 4.9L (Deceased), 1991 Cadillac Sedan DeVille 4.9L
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105 Posts
Discussion Starter #3
Very informative! Thanks!
 
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