ive searched for hours and was not able to find what i was looking for.

i need to set my timing on my 89 trans am 350 w/ tpi wiring and dizzy, ive found the est and unplugged it, then i rotated the dizzy counterclockwise and i stopped when the mark got to 6 @ idle speed. heres an ilustration


^thats 6 degrees BTDC correct?
when i plug the est back in and check it w/ my timing light at ~2400rpms my light reads 54 degrees.

What am i doing wrong??

 

You're not doing anything wrong. You set the static timing, the computer sets it dynamically (adjusting for RPM and load). Don't worry, be happy. :-)

 

Agreed, sounds normal.

 

thanks for the reply, when is it that full timing has to be at ~37 @~2500 rpms then? carbd cars? <- thats what threw me off

i have a mild cam, should i try taking it back to 8degrees instead of 6? i will test and tune at the track on saturday.

heres why i wanna get the timing right
https://www.thirdgen.org/forums/orga...others-m6.html

 

For a carb set-up, 36 degrees BTDC total is mechanical-only timing. Basically you disconnect the vacuum advance, run the RPMs up until you reach maximum advance, and set the timing to 36 degrees BTDC.

With computer controls, you can't disconnect the "vacuum advance". All you can do is set the "base" timing, and through ECM programming, tell the computer how much to advance the timing under power.

What you are seeing is basically what would be full advance on a non-computer system with both mechanical and vacuum. For example, 12 degrees initial advance, plus 24 degrees mechanical advance, plus 18 degrees vacuum advance. Under load, the vacuum would drop, reducing the vacuum advance (which would be zero vacuum advance at WOT).

Set your base timing where the engine runs best.

 

Actually, 54* BTDC is not correct. When you check this with the light are you back to using the 0* mark? Here is how the timing works with the ECM and distributor.

The maximum advance of the distributor itself is 42 degrees. More then this and the rotor is closer to the previous cylinder. Which means that if 44* is programmed into the distributor the engine shuts off. As it is sparking on the already previously sparked cylinder. I've done this as a test and know it is true.

With the base at 6*, plus what the distributor can add (42*), the maximum timing at the crank is 48* (42 & 6). The ECM makes sure that the distributor timing is never more then what the distributor can add. This is 42*. In this calculation (within the ECM) the base timing is not included.

So if you are seeing 54* at the crank, either the wrong timing mark is being looked at, or the dial back light is bad, or the timing tape is incorrect.

RBob.

 

i have 2 timing lights, one with the dial and one without. Ive tried both of them and at idle w/ the est disconected i get the same degree of 6.

I rechecked it today and with the est plugged in i saw, according to the dial, 54* by like 2500rpms.

If i disconnect the est and try giving it gas it backfires through my intake.

I drove the car today as it is right now, 6*btdc and it ran fine, there is a lil bit of bogging when i first give it gas under 2000rpms but then it hauls ***.

 

The backfiring with the EST open is normal. Just not enough timing.

I woudn't worry about the dial-back showing the 54* BTDC. As it is I've always wondered how they could be accurate at various RPMs. Not to mention different cylinder counts (4 cyl engine vs. 6 vs. 8 cylinder engine).

RBob.

 

I know this might be off topic but i have a 91 camaro z28 5.7 tpi. and i do not know what to unplug to set the timing. i put a comp cam and some other mods but i need to know what exactly to do to get the timing set.
Thanks

 

Under hood, passenger side, near the A/C box on the firewall and upper strut mount, there is a single wire with a connector that protrudes from the harness. Tan wire with a black stripe.

That is the EST or BYPASS connector. With the engine running and warmed up unplug that connector. The SES light will turn on and the timing will go to the base setting. You can then set the timing.

To get normal timing back need to turn the engine off (key-off) for a minimum of 5 seconds. Note that this action will also set code 42 in the ECMs memory. So expect that if you blink the codes or check them with a scan tool. After 50 starts with no error this code will self-clear.

RBob.