I have a 1985 TA with a 305 TPI, A/T, A/C that I have just replaced intake manifold gaskets on. After finishing the job I looked through my factory service and Haynes manuals for ignition timing specifications, but both refered me to the underhood emissions sticker. My car does not have the original emissions sticker for the ignition timing settings and procedure. What would be really cool is if anyone could give me a pic of their underhood emission sticker. If anyone could help me I would greatly appreciate it. Thanks, Sisco

i have an 88 with the same problem did you ever find out what the timing is?

Some where 6 A and others 0. What chip (memcal) is installed? Base timing has to match the chip.

Gary,

Sorry it took me so long to reply. I found that the timing specs for my 1985 Trans Am, F VIN engine are: 6 degrees Before TDC at 500 rpm. I received some of this info from Jason Scott the editor of Pontiac Enthusiast Magazine, which I though was really cool of him to take the time to help a gearhead out. Here's some excerpts from the conversations that Jason and I had:

Jason's Reply to my initial timing question: I don't have an '85 T/A handy, but the shop manual shows that your timing should be set to 6 degrees before top-dead-center (TDC). You'll also want to make sure that your knock sensor is functioning properly, as that is what actually controls the timing (the computer will add in timing until it detects knock, then back it down until the knock goes away).

My reply back: Thanks for such a quick reply. Do you know at what RPM I should check the timing? I found the following info at AutoZone.com but it does not give me an RPM to check the timing at. http://www1.autozone.com/az/cds/en_us/0900823d/80/1e/ee/6f/0900823d801eee6f/repairInfoPages.htm

Jason's final reply: [FONT='Verdana','sans-serif']Glad I can be of some assistance.

Engine rpm isn't actually related to timing, if you're checking the timing properly. The reason is that you have to disable the advance mechanism, and once you do that, the timing will remain "static" regardless of engine RPM. On a TPI car, this is accomplished by disconnecting the brown+black-striped wire that runs to the distributor. You'll usually find the wire -- and a conveniently located connector for disconnecting it -- along the firewall, above the heater blower motor, where it exits the wiring harness. Alternatively, some cars (like my '92 1LE Formula) have the wire along the firewall, behind the distributor, and slightly toward the brake booster.

Normally, the advance mechanism advances timing (to fire the spark plug earlier), because there's physically less time for the spark to ignite the air/fuel mix in the cylinders, so the plug has to be fired sooner to allow enough time for a complete burn. The catch is that you want the plug to fire as late as possible so that cylinder pressures are as high as possible, because that makes for more power. That's why a knock sensor is so important: it determines when the timing has retarded so much that detonation begins to occur, so the knock sensor has the computer re-advance the timing slightly, until the knock goes away.

But when you disconnect that wire, the timing won't change related to engine RPM, so you can set the timing, then reconnect the wire. The timing will change considerably when you reconnect the wire -- that's what the computer is supposed to do.

BTW, the idle speed for a manual trans car is 750 rpm; 500 for an auto (though that strikes me as low).[/font]


I also found the information on the AutoZone website at the following link: http://www1.autozone.com/az/cds/en_us/0900823d/80/1b/fc/d0/0900823d801bfcd0/repairInfoPages.htm
I was really impressed with the AutoZone site's repair information section. There's all kinds of good Third Gen info in there.

I hope this helps you and many other Third Gen folks out there,

Sisco

Gary,

I forgot to tell you that the timing specs are in figure 1 of figure 2 of the link below, depending on the year of you car. http://www1.autozone.com/az/cds/en_u...rInfoPages.htm

Sisco

These two replies seem to contradict each other.

The first post is how I have understood it to happen, computer adds timing (spark adv) and the knock sensor removes it (spark ret).

"That's why a knock sensor is so important: it determines when the timing has retarded (advanced?) so much that detonation begins to occur, so the knock sensor has the computer re-advance (retard?) the timing slightly, until the knock goes away."

Any words of wisdom on any of this?

Jason:
"The catch is that you want the plug to fire as late as possible so that cylinder pressures are as high as possible, because that makes for more power."

This is why more timing advance is not always better, and how with less spark advance there can be more power and/or detonation. There can be a too early spark detonation limit and a too late spark detonation limit.

As the spark timing is advanced from TDC, the piston is trying to compress a burning, expanding fuel charge. This will have a limit as to more power, and a lot more heat will be generated (bearing loads are a lot higher).

As the spark is moved (retarded/less advance) closer to TDC the cylinder pressure is higher due to static compression, firing the spark into this higher pressure gas will tend to increase power and/or detonation. (the higher pressure is more likely to explode, not burn).

The sweet spot could be wide and not make much difference where the spark is set, or maybe no sweet spot at all.

The type of fuel (octane higher = less detonation), the amount of fuel (richer = less detonation), heads (aluminum = less detonation), or cylinder temp (hotter = more detonation, more egr = less detonation), compression (higher = more detonation) will all be variables in this.

If you can build an engine, and find this sweet spot, through all the rpm range. You will have one sweet runing machine.