ok i dont have a problem on my fiero but i was just wondering how the computer advances or retards the timing on a distributor when its geared with the cam?

The distributor signal is locked to the cam and crank, the ECM takes the distributor signal and uses it and the map and other sensors, to put out the correct timing to the coil.
The ECM bases all of the timing on the fact that YOU set the distributor timing as called out on the emissions tag, and if it is set wrong, it could cause damage to the engine.
The ECM has a table built in that sets the timing according to the rpm, map, o2, etc. supposedly, it is like having a mechanic monitoring and adjusting engine settings for the conditions.

[This message has been edited by crashyoung (edited 06-08-2012).]

how can it damage the engine? are you just talking generally or like fiero specific?

I am talking all engines in general, and I am saying you can destroy an engine if it isn't set up right. Like trying to set timing and carb adjustments by 'ear'...
Some people think you can bump some advance timing into the base timing and get a bit more performance out of the engine. If you do this and don't run a distributor curve to see what the total advance is and at what rpm, you could get the engine to ignite too soon and cause damage from the pistons and rods being forced to try and stop crank rotation, rather than aid rotation.

oh i see, thanks! +1 for you

quote Originally posted by crashyoung: Some people think you can bump some advance timing into the base timing and get a bit more performance out of the engine.

Admittedly, I'm one of those people.

If you know what conditions to listen for "pinging", it's pretty obvious when it's occurring. Then just back off the timing a bit.

Someone who isn't sure about it shouldn't be doing timing "by ear" though, as yes, it can definitely cause engine damage if too far advanced.

I used to drag race, and when I set the timing on my engine, I had the distributor advance curve dialed in on a Sun distributor machine first, then I would install the distributor and set the base timing so the base timing and the advance would only go to a certain value at a certain RPM. With the ECM, the 'distributor advance curve' is set by the prom, and all we can change is the base setting, unless you have a prom programmer and know the coding of the prom, then you could set the curve to what your engine needs, if you know what that would be...
Now, on my Chevy 350, I had 11.5:1 compression ratio, .45 cam lift etc. etc. etc. base timing was 4 degrees BTC, I could advance that to 10 degrees at idle, but at 7000 RPM it would ping and cause all kinds of trouble. Not to mention, not run well. When it was set properly, it would turn 13 seconds flat in the quarter mile in street trim... You couldn't set that up by ear, it had to be done with the proper timing equipment.
You can do what you want with your engine, but I will use the proper tools, for best performance.

quote Originally posted by crashyoung: You can do what you want with your engine, but I will use the proper tools, for best performance.

We do the best with what we've got.

[This message has been edited by Patrick (edited 06-09-2012).]

I have a cheep timing light, it was $20 maybe? So little for such benefits. And because I assumed my timing was unchanged when I changed the cam gear, my engine was very lacking in power. After I set it to specs, the old zip was back! Fortunately, the timing was retarded, and not advanced
BTW, my very first timing light was a modified strobe light I had built. after getting a good poke from it, I invested in a real timing light. It was shocking
Some times, even this old dog forgets to start with the basics.

ah, this doesnt directly relate to why i asked the question but i timed my 4.9 by ear. its not excately where it supose to be im sure of that but i was reading on the chilton manual on how to time it and it really didnt give specifics for it. all it said was rotate cyl 1 to tdc and position the distributor so that its on plug 1. so im assuming it fires at tdc. its just odd they would tell me to use a timing light.

quote Originally posted by Niterrorz: ah, this doesnt directly relate to why i asked the question but i timed my 4.9 by ear. its not excately where it supose to be im sure of that but i was reading on the chilton manual on how to time it and it really didnt give specifics for it. all it said was rotate cyl 1 to tdc and position the distributor so that its on plug 1. so im assuming it fires at tdc. its just odd they would tell me to use a timing light.

That isn't tuning by ear, that is a static timing method. It allows you to be in a safe running mode so you can then time it with a light. But that works best with points, in fact, some marine and aviation engines are only timed with a lamp and battery.

The nice thing about todays engines with auto advance/retard control is, we don't have an extra lever on the column for adjusting the timing. I had a tractor with that setup... You would retard the spark for easy startup, then advance it as you needed. There is where you learn to tune by ear! Mostly, as the engine rpm increases, you need to advance the spark timing to get best efficiency from the fuel. As the load increases, you want to retard the spark to prevent pinging. So you need to keep an eye on the row you are cultivating, a hand on the steering wheel, and an ear on the engine. Gets complicated, thats why we have auto advance.

For in depth info, look up race engine timing, it is quite interesting.