bad03chief

Hi guys,

I'm trying to set the timing on my camaro. I recently put a used ECM and was trying to set the timing. With the ECM timing connector connected, the timing is about 1 division above the last timing mark. (beyond the last timing mark) (bottom picture) When I disconnect the ECM timing control, the timing reads 4 degrees TDC. (top picture) Could it be that the used ECM i put in is bad, or has been programmed to hold the timing at 16 degrees BTDC?

See pics below

bad03chief

Just for clarification, I set the timing to 4 degrees BTDC with the ECM connector disconnected. I shut the car off, disconnected the battery and reconnected the ECM timing connector. Reconnected the battery, fired up the car, and the timing shows north of the furthest mark??

Reid Fleming

iTrader: (2)

There are two variables at play here. "Base timing" and "Total timing."

What you need to do is disconnect the tan wire up by the passenger side area. You are already doing that.... This disconnects the automatic variable "total" timing that the ECM controls. Doing this allows you to set the "base timing." If you were to take the car for a drive around the block like this, you'd find it runs terrible. That's because the timing would be locked at 4° BTDC.

With the wire disconnected, set the timing at 6° BTDC. You could even try 8° if you want. But 6° is stock.

Plugging that tan wire back in allows the ECM to change the "total" timing depending on throttle acceleration. It might be 18º before at light throttle. 25° before at medium throttle. And 34° before at full throttle.

If you change the base timing from 4° to the 6° mark, the above numbers would be 20°, 27° and 36°

Those teeth marks that show you timing numbers are only useful for setting "base" timing. It makes complete sense that the numbers would be off the scale with the tan wire hooked up.

bad03chief

The base timing is way off Reid. I adjusted the the timing several times with the tan wire was disconnected. No matter where I adjust the base timing (with wire disconnected), the mark is where you see it when I reconnect the tan wire. I did not see this before I changed the ECM. I live in Cali and must keep the timing at OEM specs. I think 6 degrees BTDC at idle.

bad03chief

Wait Really. Makes sense that the I would be off the scale with the wire connected? If the ECM controls the timing, why would it be checked under normal running conditions with the tan wire disconnected? It runs great, I just don't remember verifying the timing before with the wire disconnected.I thought that you only disconnected it to change the time?

Appreciate you feedback,

Rick