Ignition Timing Issues???? 1992 K1500 5.7

[shibbershabber]

Okay. 1992 K1500 Suburban 4x4 / 5.7 / TBI / AT 149000 miles

In trying to diagnose another issue I went out and checked my timing...

With the timing advance wire disconnected, at operating temperature... the sticker says that it should be 0 degrees

below is a diagram that shows what my timing tab looks like. I was told by another member that the notch by the 'tube' was 0*

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I am not sure where exactly that is measured. My truck represents the green line, should I be at the red line? which is 0 degrees?


So when I plug the wire back in and check the timing at idle, turning the advance know on my light.... it lines up (greenline) at about 21 degrees

HOWEVER! When I am looking at it at this point there is some fluctuation in the reading... the line appears to move erratically ... no idea how many degrees but it looks like 1/8 to 1/4 of variance...

Whats up?

 

[firefighter_2319]

should be the groove before the tube is 0* with the wire unplugged