I have 91 Firebird V6 that is in time at 10BTC when the EST is disconnected, but when the EST is connected it advances to about 26(somewhere over 20).... it was running alright until i changed the (Gutted) Catalytic converter and Put in exhaust manifold gaskets, i also cleaned my EGR stem, i have checked vacuum lines, all my spark plugs and even went as far as to change the Brain and put the old CAT(gutted) back in.. We have timed it following Ignition timing procedures and it is in time when the EST is disconnected but not when it is connected. Engine is throwing no codes when we run a scan engine jumps between 730RPM and 919 RPM and will not hold at desired 787 RPM indicated by the reader. Throttle Position Sensor??! i was thinking,,,,, but wouldn't that throw a code?? I have replaced the ignition control module before, the Distributor, Plugs, Wires, ECM, Ignition Coil, Oil Sending unit, Fuel Pump, 02 Sensor, Injectors, and Battery. The only thing i could think of was the vacuum line because we cut and spliced it, but we spliced it.... meaning it should work and i see smoke by the EGR stem (just a little) i thought maybe was anti seize from putting the new stock exhaust manifolds on(Old ones were broken at the bolts connecting to the pipe). Please help i cannot figure it out for the life of me and i just keep pouring money into this car, and i almost feel like i should've taken the LT1 outta my z28 im trying to sell (to fix this car)...

 

As it is supposed to.
The spark advance s not static , it is changed to accommodate different engine loads and speed
At idle there is no load on the engine so the computer advances the spark to the figure you are seeing

If you did the same timing check on a old skool dist engine you would see the same effect as the weights, springs and vac advance do to the spark advance what the computer does in a EFI car

The whole reason for disconnecting the EST is to take away computer control while you set the static timing;
if you left it connected , everytime you moved the dist to get the timing right the computer would keep changing it

 

Ahhh gotchya, why am i still having a horrible misfire though? it'll lose power while driving and the motor feels like its going to vibrate itself to death! with a timing light i can see the misfires yet no codes are showing up. i checked it with an auto x-ray and got nothing to show up when i ran a scan,...

 

also, it says my ECM is running in open loop, a friend of mine said it should br running"closed"... thank you for your insight i very much appreciate it!

 

When?
There are timers that make it go into closed loop after a certain time and when the engine get up to a certain temp
If it is still in OL after it has warmed up ,look at the O2 sensor readings on the X-Ray and see what is showing ?
If the ECM doesn't see the correct input from the O2 sensor it will never put the engine into CL

 

I've gotten it to run temp while the X-ray was connected. I didn't look at what the 02 readings were, id just replaced it not to long ago (about 2 months) I work two more 12's (tonight and tomorrow) so monday ill probably put the X-ray on it again and see what it says, ill see if i can take a video and upload it so you can see, if i cant figure it out..

 

hi i have an 89 camaro 2.8 with the same problem could it be the ignition mofule?

 

Did you read post # 2 above ,that is how it is how the EST is supposed to work