Timing my 1997 4.3 ltr. GMC?

Question

I pulled the distributor on my 97 4.3ltr gmc and like a dope forgot to mark it. Now I am trying to reset the timing but it's not going well. I set the motor at TDC#1 and the timing marks line up perfect. I used a screw driver to turn the oil pump then dropped the distributor back in so that the rotor is lined up with the arrow. Now it starts, but runs rough. I put a timing light on it and it looks like its about 20 degrees advanced. Since the distributor is not adjustable I don't know what to do next. I have repeated this process a few times to insure everything is where it belongs, but it all apears to be right. What should I do?

I appriciate the responses, however so far none have directly applied to the vehicle in question. This is a tricky one boys!

Answer 1

The distributor may be 180 degrees out. Pull the distributor out a few inches and rotate rotor 180% and drop back in. See if that works. It won't hurt anything to try. And make sure you put the wires on in the correct firing order first.
The firing order is 1-6-5-4-3-2
DISTRIBUTOR ROTATES CLOCKWISE.
You may have put the wires on from the wrong starting point and may have to move all the wires one pole over to compensate to 20 degree difference. if you move them one over clock wise and it gets worse then move them 2 poles counter clock wise and see if improves...I hope I'm not confusing you with my description.

Answer 2

Also need to put the ignition in By-Pass to set the timing. It should say on the emission sticker how to do this. It involves disconnecting a wire connector temporarily on the ECM wiring harness(tan w/white stripe wire?).Depending on the model,this connector is near the firewall in the Eng. compartment or below the glove box near the floor inside. The "service Eng soon" light will come on during this process, but will go out after reconnected and restarted.