drk421

So I'm trying to figure this one out...

I've got a 351W with an MSD 8354 ready to run distributor, nothing fancy going on.

Normally, when its cold, it runs really good, and the positive side of the coil is exactly 8-10 volts. After it warms up, the tachometer starts jumping all over the place. I put a meter and a light on the positive and of the coil, and noticed that when it starts acting up, the voltage goes up to 12V, and the light flashes randomly. This would obviously cause a problem for the distributor.

I tried hooking up the coil and distributor directly to the battery (bypassing the ignition switch), and got the exact same result.

The weird thing is, if you shut it off for 1-2 mins, and start it back up it, it runs fine again for a few mins, then starts doing it again.

Any ideas?


EDIT:

Oh, forgot to mention I've already tried replacing the coil, to which didn't have any effect.
I'm going to guess that the distributor is the probably the problem.

Haywired

The trigger in the distributor is going bad , had the same problem but mine got to the point of not running.

KMatch

For voltage to be pulled to 8-10v requires a load on the circuit to load the resistor wire. When voltage goes up, the load is likely less. If adding 12v to the hot side makes no difference, start looking at the ground side before replacing parts. Hook your meter up with the black lead to the battery negative and the red lead to various grounds related to every part in question including the engine block. Anything over .2-.5 volts shows a ground problem.