K1500 Timing / Distributor Replacment - Backfires

[93gmc$$]

I have a 93 K1500 with the 4.3 V6 (Z). I replaced the distributor, cap and rotor. I verified #1 TDC thru the spark plug hole--the timing mark on the drive pully is right on. I adjusted the oil pump drive pin to center the new distributor. I put the wires back on the cap in the same order (1-2-3-4-5-6) as when removed. I disconnected the set timing connector at the firewall. When I try to turn the engine over it backfires almost immediately (KABOOM with a nice fireball). What have I messed up? Am I a few dgrees off or 180 out? Is there something else I have not thought of? I can't check with a timing light until I can stop the massive backfiring.

 

Moderator--you can delete this post, I reposted it in the engine section where it should have been in the first place...