154 random frequent misfire

[Duner]

Coil has been on tractor for years and is the same as when I purchased the tractor.
I can't find any labels on the coil. I thought all 154.185 and 184 came from factory with true 12 volt coil with no external resister needed. I have spare coils and will try one or three to see what happens.

[Gary Dotson]

Just measure across the two post with an ohm meter. Internal resister coil will measure in the 3 ohm range, non internal resister will measure approx. 1.5 ohm,

[Duner]

The coil on tractor is 3 ohm.

[Jim Becker]

I've been following this thread, but not had any useful suggestions. There are only two things I can think of that a running alternator could produce that causes the problem: 1) voltage too high for some component. 2) some weird (possibly) FR noise that causes a component to misbehave. I guess you could do some experiments to try to prove one or the other. You could try temporarily adding a ballast resistor to the circuit (even though the coil doesn't call for one). If it makes the problem go away, voltage is the problem. Of course, that still won't tell you which component is the problem. The other diagnostic trick that comes to mind would be to add a choke to the output line of the alternator, something like a ferrite ring. If I was to try that, I wouldn't be sure I had actually done anything. Again, if it worked you still wouldn't know what component was the problem.

It seems the condenser is the part most likely to be sensitive to either of these. You have replaced it. But have you only done that once? New condensers these days don't seem to have much quality control. There is a significant chance that you replaced an old bad condenser with a new bad condenser. Try another one, preferably one you can temporarily rob out of something that is working.

[Eugene]

I've been following this thread, but not had any useful suggestions. There are only two things I can think of that a running alternator could produce that causes the problem: 1) voltage too high for some component.

Disconnect Delco 10si alternator, miss goes away. Install Delco 12si . Still misses.

Voltage check at battery.

[Duner]

Voltage was OK. 14.2 when I first started it and 13.6 volts a bit later.
I will post back when I get it figured out. You can bet it will be really simple or stupid .
Thanks!