Half Power

Spark plug extenders?

 

Try switching the digiplex plugs and see if the bank switches.

 

If you lost a whole bank (4 cylinders) it could not reasonably be plug wires or extenders. The odds of all four of either wires or extenders failing (or a combination) at the same time are astronomical against it happening.

 

When you say you replaced the coil do you mean the entire unit (i.e. w.ignition module) or just the coil itself? Mine just lost a bank due to the module, $16 to replace (thanks Steve M!), or keep a spare.

 

Yes, it could be if you have a points-based system and the point(s) in one distributor are on the verge of working/not working (so sometimes it works and sometimes it doesn't). Also, the dist rotor, cap center contact button, the cap itself can all have problems -- even a poor connection between the cap and the coil wire could cause your symptom (i.e., your going to at least have to have a look inside the cap to see if things are OKish). But first, please describe what type of ignition system your '79 308 has:

Stock dual US distributors with R1 and R2 points each running a conventional coil

Stock dual US distributors with R1 points only each running a conventional coil

Stock dual US distributors with an aftermarket triggering system running conventional coils

A single euro distributor with two (R1 only) points running conventional coils

something else...?

 

Nice to hear that you've got an unmodified US '78-'79 308 stock ignition system -- most aren't

First thing to do is the simple stuff: inspect the inside of the cap, the rotor, the center button + spring, and measure the resistance from the brass fitting holding the center button inside the cap to the metal fitting on the other end of the coil wire that goes into the coil snout (to check the screw-pierced electrical connection between the coil wire and the cap, but since you are right there anyway, I'd remove the coil wire from the cap, cut 1/4" off, and reinstall/repierce with the screw). Additionally, never hurts to make sure all the wire connections at the coil and the ballast resistor seem OKish -- if one of the nuts fell off that would be trouble

If that all looks OK, but you're still having trouble...

Ideally, to check the functioning of the points, it would be best to make a dwell measurement -- i.e., hook the dwell meter from the "R1" labeled post to ground, and measure the dwell with the microswitch closed at idle (R1+R2 functioning) and when the throttle is slightly opened, so the microswitch is opened, (only R1 functioning) -- if either of these are a crazy value (or an unstable value) compared to the WSM specs that would be a clear sign the points need some attention. If you don't have a dwell meter, you can always just try to confirm the physical distances of the point contact opening action for both R1 and R2 (and a visual inspection for obvious trouble, like a broken/pitted contact point face or broken wire never hurts).

Good Hunting, and give a shout if we can help...