Engine miss when distributor vac advance hooked up??

[Brutal6]

85 Bronco 2, 2.8, Durasparked. Engine starts and runs, idles smooth, and I'm happy with it. Timing is set at 11 degrees BTDC. However, when the vacuum advance is hooked up it has an intermittent miss that won't go away!!??
Any suggestions are appreciated.

 

[Uncle Gump]

I have seen where the pick up coil wires fatigue over time. Typically the wires Crack right where they meet the pickup. This is due to the breaker plate being advanced and not with the vacuum advance. I've seen them bad enough it will actually kill the engine with vacuum applied and start running again as vacuum is lost.

 

[JerryC]

First thing that comes to mind is a leaky vacuum advance diaphragm on the distributor.

 

[Brutal6]

Thanks for the replies. I hooked the vacuum advance to ported vacuum and now other than a miss or 2(sometimes) off idle it runs smoothly, don't know why but it does. It also runs smooth with the vacuum advance hose plugged, just doesn't seem to pull the hills as good with the vacuum advance hooked to the ported side.

 

[Uncle Gump]

Thanks for the replies. I hooked the vacuum advance to ported vacuum and now other than a miss or 2(sometimes) off idle it runs smoothly, don't know why but it does. It also runs smooth with the vacuum advance hose plugged, just doesn't seem to pull the hills as good with the vacuum advance hooked to the ported side.

So... when you connect a manifold vacuum source to the distributor... does this miss happen at the same time? I mean like instantly...

If that is truly the case I would be suspect of the pick up wires as I stated before.

 

[Brutal6]

The last couple of times I've started and driven it there is no miss?? I'm guessing some debris got into the vacuum line causing the miss??? I may pull the distributor and do a close look and cleaning and see if anything may be amiss.

 

[JerryC]

Hook up a vacuum pump to the distributor. You can get a cheap one a Harbor Freight.
That will tell you if:
the vacuum advance works
the diaphragm in the vacuum advance is good (holding vacuum)
if the advance is causing the miss.

 

[Brutal6]

Did a 90 mile trip today and the B2 worked/ran like a charm. I did most of the test that were suggested in the previous posts and all checked out okay....thanks to all. The vacuum advance system appears to be working okay. It holds a vacuum, so evidently it's working okay, and the engine idle responds when vacuum is applied to the cannister.
Again, I do appreciate your help