Setting timing question

[hotpsca]

After a full tune up I trying to set the timing on my 1995 4.3 astro van:
Engine is on TDC, the computer wire is disconnected , timing marks line up perfectly with the timing light(0). My question is after reconnecting the computer wire I recheck the timing and is about 10 degree after TDC. Is this normal?

[Leeann_93]

Yes. That's why you have to disconnect the timing wire in order to set to 0°. The computer automatically sets the timing based on the conditions it sees - temperature, elevation, octane, load...etc.

[hotpsca]

Thanks, I was just wondering because the van seems to run better with the computer wire disconnected.I will take for a drive to see if the computer adjust the timing to a smooth running engine.