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Setting Timing (Age)
02-02-2012, 10:47 PM
Post: #1
Setting Timing (Age)
1990 Cadillac Deville 4.5 L FWD
180,500 miles

When setting the timing on this vehicle should I set it to
the 10 degree's BTDC per the Haynes manual ?

What are the myth's truth's about setting the timing a little bit
advanced on vehicles with higher mileage on the odometer engine ?
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02-03-2012, 11:10 AM (This post was last modified: 02-03-2012 11:11 AM by Rupe.)
Post: #2
RE: Setting Timing (Age)
If the manual agrees with the emissions sticker then by all means do it.

Now, I have to ask why the timing needs to be adjusted? Since there are no points (not since the mid 70's) then the only issue might be a worn timing chain causing the ignition to be a bit retarded. Usually this is no more than a few degrees.

As for the myth, it's just that. These days *IF* the timing can be adjusted you should aim for the factory spec. The reason being is that advancing it too far will cause an increase in NOX emissions even before ping happens. If your car happens to have a knock sensor you may not hear any ping but it will run hotter, which can damage the cat converter. It may also cause the check engine light to come on as the ECM constantly tries to correct other things. Conversly, too retarded will also cause the cat to run hot due to unburned fuel getting further down stream into the exhaust. Basically you should aim to get it as close to spec as possible to keep everything happy. There's little to be gained by fooling with it and you can possibly open up a new can of worms.

Oh, in my state (Ct) if all is not well you may flunk the annual emissions test.
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02-05-2012, 12:42 PM (This post was last modified: 02-05-2012 01:09 PM by cferry7.)
Post: #3
RE: Setting Timing (Age)
(02-03-2012 11:10 AM)Rupe Wrote:  If the manual agrees with the emissions sticker then by all means do it.

Now, I have to ask why the timing needs to be adjusted? Since there are no points (not since the mid 70's) then the only issue might be a worn timing chain causing the ignition to be a bit retarded. Usually this is no more than a few degrees.

As for the myth, it's just that. These days *IF* the timing can be adjusted you should aim for the factory spec. The reason being is that advancing it too far will cause an increase in NOX emissions even before ping happens. If your car happens to have a knock sensor you may not hear any ping but it will run hotter, which can damage the cat converter. It may also cause the check engine light to come on as the ECM constantly tries to correct other things. Conversly, too retarded will also cause the cat to run hot due to unburned fuel getting further down stream into the exhaust. Basically you should aim to get it as close to spec as possible to keep everything happy. There's little to be gained by fooling with it and you can possibly open up a new can of worms.

Oh, in my state (Ct) if all is not well you may flunk the annual emissions test.

THANK YOU

Yes - This vehicle has a distributor hold down bolt for timing adjustment.
It probably did not need to be changed.
I wanted to see ( Play ) if adjusting timing a bit would help gas mileage,
before I could R/R spark plugs and wires.
Plug and wires replacement on 2-03-12 have improved MPG in the city.
Need to do other little tune-up items. Have yet to do a good MPG test on Hwy.
Real time responses -here great !
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02-05-2012, 09:30 PM (This post was last modified: 02-05-2012 09:31 PM by Rupe.)
Post: #4
RE: Setting Timing (Age)
Sorry for the delay. I saw your reply this morning but not after you did the edit to get your part in.

By all means, change the fuel and air filters as it will help in the long run. So will a cap and rotor change. At that age and mileage you should take a gander at vac lines too. You never know if one is cracked or collapsed and doing something odd to the system. A can of good injector cleaner is probably due by now as well.

As for the timing "fine tuning" you might slide it up say 2 degrees over factory just to pick up any slack in the timing chain but I wouldn't go any more than that just to be on the safe side. Anything you gain will likely be in "open loop" while the engine is cold. After that the ECM takes over.

Let us know how you make out.
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