distributor and advance

[aficio]

1987 r20 pickup 454
All: in fighting my bogging problem, i replaced the pickup coil in the distributor, when I was removing it and before I loosened anything I marked three points on the unit and once i put it back in i lined all three points up, but when i started the truck up i had to rotate it almost a halve the distance to the next plug. and with the timing set i am not even close to my marks, actually quite a ways off. any ideas what would have caused it. In the original position my crankshaft mark is not even visible, it is about 12 o'clock instead of matching on the indicator to set my degrees.
thanks

[Desert1957]

Timing on these "TBI" engines is not like any other square.
Its been covered many times but there is a wiring plug near the master cylinder , on the firewall which must be unplugged to set base timing.
http://67-72chevytrucks.com/vboard/s...ght=TBI+timing



Desert

[Sodell]

And after you unplug, set timing at zero.

[aficio]

Thank you, thank you, my manual does not say a thing about this and i could not figure out what i could have possibly done, i appreciate it very much.

[aficio]

So even though the truck say's 4 btdc. you set it at zero? so does the computer take it to 4 btdc once you hook the line back up and clear any codes?

[Sodell]

If it is a TBI, you set it at 0, the ECM will take care of everything.,

[aficio]

thank you. Will reset tomorrow night and see how it works