No Power From Coil

[jrcotner]

Tried to start the Pinz this morning and it turned over fine but would not hit on any cylinder. Fuel is flowing to the cylinders. I put a spark tester on the coil wire and am not getting anything. I also checked each plug wire and am not getting anything there, either. The wires leading to the coil are good and the coil wire and plug wires are less than two years old. I have a Petronix ignition installed by EI. It ran fine when I parked it two days ago. Before I run out and get a new coil is there anything else that may cause this?

[pcolette]

You mentioned that the wires leading to the coil are good. Did you mean they are in good shape or that they're suppling power to the coil? If you haven't checked for power to the coil I would do that first. If there's no or low power to the coil then I think it's possible the 4500RPM module has failed. If so, the plug to it can be easily jumped to get you going. There's a 6 position plug on the module. To jump it, remove it from the module and use 2 male spade terminals and a short piece of wire to connect the 2 center terminals to each other.

[jrcotner]

The power to the coil is 24.8v. Forgot to mention that.

[jrcotner]

I've never had a coil just go dead before. With voltage coming in but nothing out it seems to be the coil, but I'd like to hear from anyone out there if it could be something else.

[kdiqq]

I've seen coils fail, but never on a Pinz. Then again, my Pinz experience is SUPER limited. If you have voltage going in to the coil and none coming out (checked at the other end of the coil, not the distributor) I'd say that's a complete enough diagnosis to blame the coil. If I were in your shoes, I'd be replacing a coil.

[Jimm391730]

If the coil + terminal stays at ~24V when cranking, it sounds like the negative (-) terminal is not being pulled to ground; either the Pertronix is dead or loose or bad connections between it and the coil negative. If you get ~24V on the coil negative while cranking, this confirms it.

[jrcotner]

Thanks for the advice. I'll do the voltage test while cranking and check the Petronix connections.

[jrcotner]

I checked the cranking voltage and here's what I got:

Coil (-) while cranking: 9.3v max (variable)
Coil (+) while cranking: 21.5v

I checked the Petronix connections and they are solid and the wires in good shape. I checked the coil ground and it is good. The magnet has the correct gap, the plugs wires are all connected to the spark plugs, and all the other electrical connections seem alright. Does this leave me with a bad coil or Petronix?

[Jimm391730]

From the answers you have given, I think it is most likely a bad coil.

[kdiqq]

Wait. You're pulling a POSITIVE voltage on the ground side of the coil?? Did you check for continuity from that terminal to another ground location?

[Jimm391730]

No, the positive voltage on the "-" coil terminal comes from the positive terminal, through the coil primary. This happens when the "points" (now Pertronix) are not closed to ground. When the points open and do not ground the negative terminal, the 24V on the plus terminal gives the negative terminal 24V, too (they are connected together by the primary winding). When the points close, the negative terminal is pulled to almost zero volts. So as the points open and close during cranking the average voltage is somewhere between these two. So the "9.3 volts max (variable)" that was measured makes perfect sense, and shows that the points (Pertronix) seems to be working correctly.

This also means that the coil primary is connected, but this is the low turns, thick wire portion of the coil winding and isn't easily damaged. The coil high voltage output is developed from the secondary winding, made from thousands of turns of very thin wire (with lots of insulation to prevent failure from the high voltage). But eventually the insulation does fail and this winding shorts out, burns up, and no spark voltage is produced. This is what seems to have happened.

The reason the coil has terminals marked "+" and "-" is that just like arc welding, one side of the spark or arc carries the majority of the heat. In spark plugs, the center electrode is tungsten, platinum, or other "noble" metals because they can take the heat of the spark arc. The ground electrode (the one that is bent to change the gap) is just cheap steel; that side of the arc is much cooler and doesn't eat away at the steel much. So the coil has a polarity on the primary terminals to ensure that the polarity of the secondary (where the high voltage comes from) will match what the plug expects. Wrong polarity won't make the spark any less and won't hurt the coil, it will just eat up plugs much faster than expected (the ground electrode will erode away).

Lastly, the spark voltage from the coil is mostly dependent on the gap that the spark has to travel - the plug gap, the rotor to cap gap, and sometimes the central button between the rotor and cap. The smaller the gap, the lower the voltage. If the gap is huge, or not really even there (like disconnected plug wires) the coil can be damaged as the coil voltage goes way higher than intended when trying to jump a huge gap. When "testing" ignition, a path for the spark should always be provided (not that we do - me included) to prevent damage to the coil. This could be as simple as a screwdriver stuck into the coil wire, where the metal shaft of the screwdriver is close to a ground point to give a place for a reasonable length spark to jump. Without this path the coil voltage could be high enough to damage the coil -- most of the time we get away with it, but not always.

[jrcotner]

Thanks Jimm for the very well considered answer. I never fully understood the inner workings of the coil, but your answer makes it clear. I'll replace the coil and report on the results.

[edzz]

Jim M. I always enjoy your explanations, I learn things my college EET program left out or that I couldn't grasp at that time.


I wouldn't expect the recall is still active after all this time however this may give a hint as to your problem.


viewtopic.php?t=4935&highlight=coil+recall

[Texas710]

Might explain why there is a flame thrower in my spares from the PO, but not installed. Learn something new everyday...

[edzz]

Might explain why there is a flame thrower in my spares from the PO, but not installed. Learn something new everyday...

Quite possible that the PO got a replacement coil from Scott put it aside as a spare and never returned the old coil to Scott.
By the time I contacted Scott he was requiring (and reasonably so) a deposit before he would cross ship a replacement under warranty as too many turds had failed to return the old coil there by preventing Scott from getting refunded by the manufacturer.

Hard for me to understand people that would screw one of the few parts suppliers around when he was going out of his way to help people keep their trucks on the road and trail.

note the description of the recalled coils in the link I posted.