6.7 volts is fine. But the resistance is high and not consistent with 6.7 volts, so it may be that part of it is in the wiring from the ignition module to the resistor and not just the resistor. Something isn't quite right.

 

His meter is reading over an ohm with the leads touching....

It needs to be zeroed.
I dont think it's accurate to just subtract that number from the reading he's getting.

 

Thanks Ard,

I agree that operator and device error is a distinct possibility. I dont understand that particular Ohm reading either because it doesn't make sense, however the value on the meter was stable and not bouncing around like I wasn't making good contact, and I got the same value a of couple times.

I will see about borrowing a better device and getting something to probe down further into the socket to try that test again, but note the white wire test came out with a much lower resistance value and backing out "the margin of error" does put the lug to lug coil resistance values in spec and consistent across all three coils I tested.

 

There should be no resistance between the coil wire and the bypass in start.
After all the coil should see full voltage when the timing retard feature is engaged.

 

Agreed.

Since disconnecting and reconnecting the horseshoe connector (to another coil) appears to help the situation I still wonder if it's the connector itself and not actually the coil?

Fortunately a new horseshoe connector is cheap and available so with everything that's been happening there's really no reason not to replace it and clean up the tach wiring while I'm at it.

Beyond that I have heard the resistance of resistor wires will increase as they go bad. Wondering if I can get a ceramic Chrysler resistor and hot wire the coil from the battery if I ever get into a pinch. Also wondering if I could use the same resistor to safely hot wire the fuel pump via the fuel pump bypass wire.

 

As long as the resistor is about 1.1 ohms it'll work in place of the one in the wiring harness. But, you don't want to use a single resistor for two things. Since the voltage drop (E) equals the current through the resistor (I) x the resistance (R), if you put something else on the same resistor you'll have more voltage drop than you want.

 

I missed this when first posted. Any chance the "cheap aftermarket tach" could be part of the problem? You've got a questionable electronic component of unknown heritage cobbled into a very important circuit. I'm not sure how it only misbehaves under certain circumstances, but who knows. Maybe when the coil warms up and the resistance changes, the tach reacts differently. It wouldn't cost anything to completely disconnect it and see if there is any improvement.

 

That's a good thought, I'd rep you for that if I could.

 

@brnfree i have had to replace the horseshoe on my 80' 300 six. it would cause hiccups and on occasion, it would die and not start. i replaced almost my entire ignition system trying to chase that down. finally, i noticed an arch inside the horseshoe one time at night when i had the hood up and the engine running. $10 from autozone solved that problem for good. it turns out that the wire was corroded inside the plastic or had a partial break. every time i was replacing something the wiring harness would get bumped and "fix" the bad connection. i spent $10 on a horseshoe at autozone and moved on.

 

Exactly my experience

 

I got bit a couple of times with a bad horse shoe connection. It snapped on the coil tightly but not contact. Intermittent missing was the original reason to swap coil only to have a no start after. Figured out what was wrong eventually and now dont change out as many coils when similar problems arise.

 

Sure seems like a lot of votes for the horseshoe connector!

 

Update,

Replaced the coil connector and fan clutch on Sunday.

I extended the coil wiring so I could move the coil out from its stock hiding place under the air cleaner behind the A/C. Instead I mounted the coil on the vacated smog pump bracket right behind the fan. Thinking it should run cooler there.

My examination of the old connector was inconclusive but encouraging. I don't think the wire connections going into it were bad but I was reading resistance at the contacts until I scratched the surface to get to bare metal.

Only put about 50 miles on it but initial impressions are good. Fires right up (even hot restarts after sitting for an hour) and runs strong and idles smooth. The weather was warm and pulling a long hill I could hear more noise from the fan so hopefully next time over the pass it'll run cooler.

You can see the old coil over to the right behind the AC, and once I pull it out of there I'll reroute the new tach wire to clean it up.

Got a question: The grease inside the Duraspark connectors looks like white grease that all dried out. Any suggestions for cleaning and re-greasing these connectors?

 

It is not your normal grease so DON’T use normal grease. It is dielectric grease made just of electrical connections. You can get it at most auto parts stores.


As for cleaning a small tooth bush size wire bush, may be even a stiff tooth brush & carb cleaner is what I used on my John Deere tractor when hunting down an EFI issue when hot.
Mine turned out to be the in tank pump would heat up and slow down causing a surge.
Dave ----

 

Ooh, I like the relocated coil. Agreed, it should be much cooler out in the open like that. I may do the same mod as a precaution on my truck.

I'd also consider leaving the old coil installed, as a ready spare. That way, if the new (relocated) one acts up, you could quickly swap the connections back to the old one and still get home. That could be a big safety factor on the side of a freeway. Since the old one wouldn't have been energized, it would have stayed relatively cool even if still in a hotter location.

Glad the new fan clutch seems to be working out for you. Keep a close eye on the coolant level for maximum effectiveness of the fan clutch. If the coolant level is low, not enough total heat gets expelled by the radiator and so the fan clutch can't sense that it should kick on. It's a double whammy for overheating when that happens, but isn't a problem when the coolant level is good.