Coil Again

[loyalp]

I know that a few years back I replaced my ignition coil after having the problem with getting no spark after driving for a while. (It's one of these Flamethrower coils that I think I sourced from Expedition Imports to match the existing.)

It appears the problem has resurfaced. Do I just replace the coil with the recommended Bosch part and let it go for another couple years, or is there something I should be doing to diagnose what may or may not be going wrong here?

[Jim LaGuardia]

Check 2 things, charging system voltage(not to exceed 28.8V), and coil power voltage with key only on, and then while cranking.
Voltage should be 24 while cranking and 11-19 when running.
If voltages are reversed(low while cranking, high when running) the balast resistor may be incorrectly wired.

[loyalp]

Thanks Jim!

And for anyone who is not sure who they need to contact for Pinz work, I really cannot overstate how much you should use Goatwerks.

[pinzwheeling]

Thanks Jim!

And for anyone who is not sure who they need to contact for Pinz work, I really cannot overstate how much you should use Goatwerks.

+1

[David Dunn]

Thanks Jim!

And for anyone who is not sure who they need to contact for Pinz work, I really cannot overstate how much you should use Goatwerks.

+1

Brown noser! That'll go only so far to keep that Red Bull pig going
Lobster and salmon is what's going to keep it on the road

[loyalp]

Okay, all the voltages seem to check within spec, and the truck actually decided to start, run, and start again after it got hot. The coil was definitely hot after that, though.

So, I checked the Ohms with everything disconnected.

Found a website that said primary should be .75 to .81, and mine registered over .9 Secondary is supposed to be 10,000 to 11,000, and mine was 9,000.

If those ranges are correct, then I'm pretty sure this coil is toast but since the voltages all seem fine I'm at a loss as to why this is the second one I've had replace.

Here's a picture of how it's wired up to see if anyone sees anything funky:

http://picasaweb.google.com/lh/photo/FQ ... directlink

[pinztrek]

Your Ohms are all within meter accuracy range. You are measuring at extreme low & extreme high end of typical measurement with garden variety meters.

While proper ohms do not guarantee coil operation, I really suspect you are dealing with something else. I've never seen a coil that ohm'd correctly and did not spark. (thermal intermittent are a different thing)

I'd (carefully) try:

* Wiring a proper ballast value straight to 24v, and see if you get a behavior change. IE: Isolate out the current coil feed/ballast circuit

* Confirm you get spark with just a wire from the coil to a plug, should be nice & hot spark. IE: Isolate out the distributor/rotor.

* Once you isolated out the distributor, emulate the points and look for spark. IE: Make/break the the ground to the coil and look for spark. Act like breaker points!

* If your coil is getting hot to the touch, you could have a thermal intermittant. Once it get's hot, try measuring the ohms again.

If you have to replace the coil, I'd go with the proper bosch blue. Much closer to factory, won't get hot, known good component.

have fun,

Alan

[milesdzyn]

Check 2 things, charging system voltage(not to exceed 28.8V), and coil power voltage with key only on, and then while cranking.
Voltage should be 24 while cranking and 11-19 when running.
If voltages are reversed(low while cranking, high when running) the balast resistor may be incorrectly wired.

Just to double check:

Charging system voltage is checked at the battery while running, battery pos. post and ground with auto meter?

Coil power voltage is checked at the coil key on then cranking, pos. coil post and vehical ground with an auto meter?

Miles

[loyalp]

That's what I did.

[pinzinator]

This might be a dumb question, I'll admit it up front. Why wouldn't any regular 24 volt automotive coil work in the Pinzgauer? Put aside physical size and waterproof/dustproof requirements, as long as the resistance readings are close wouldn't it work? I realize that there are heat tolerances that limit usage, something could fry eventually. Too high of a voltage could cause tracking failure in the cap or wires, but how high is too high? My Pinz runs fine, I'm not planning any changes with my stock system, but have Pertronix.

[pinztrek]

Why wouldn't any regular 24 volt automotive coil work in the Pinzgauer?

There is not really any "standard" 24v coil, or even 12v coil.

Different vehicles have different ballast resistor schemes, etc.

The coil used in a pinz is electrically the same as the standard 12v bosch coil used on VW's, BMW's, MB's, etc. The ballast scheme is what allows it to be used in a 24v system. It has additional resistance to drop the voltage down to what the coil wants to see.

Put aside physical size and waterproof/dustproof requirements, as long as the resistance readings are close wouldn't it work?

This is exactly the case. Too high of a primary resistance and you don't get enough coil current which translates to weak spark.

Too low, and the coil current is too high, the coil get's hot, and life is shorted. Get way to low and life is about 5 seconds. (you burn it out)

All that said, my experience has been that most "coil" problems are actually ballast/primary voltage issues or are high voltage ditributor/rotor/wire problems.

As far as I can tell, the pinz coil is just the 3 ohm bosch blue in a different enclosure with military wire connectors.

I confirmed the electrical part years ago in an old bosch paper catalog that showed ohms, turns ratios, etc for all the bosch coils. For the most part, there are really only few bosch coil electrical approachs in the 70-80's. Everything else was just packaging/terminal differences. The main difference was that some coils had an internal ballast resistor, which will not work with the pinz.

The "blue" coil has slightly higher coil current and was used on performance vehicles. This means bigger wires, it's more expensive. And results in slightly hotter sparks. No surprise they selected it for the pinz.

Flamethrowers carry that approach to an extreme with very much lower primary resistance, with the side effect of higher current through the switches & ballast resistors than the stock pinz. May not be a problem, but I'm starting to wonder.

The old time trick is to feed the coil directly with the proper voltage and see if the problem goes away. If so, it's the ballast/switch. On a 12v car that'd normally mean jumpering (carefully) to 12v, which is typically the voltage during cranking. Once running the ballast kicks in, dropping the voltage (and thus current) a bit.

On a pinz I'd have to look and see what ballast value to use if you wanted to go straight to 24v. You might be able to go to the 12v battery post, but I'd do it carefully, and use a 5-10 Amp fuse in line.

I've posted the math in the past, it's not that hard to calculate coil currents/voltages. From memory, a bosch 3 ohm would be 4-5 amp coil current. So a ballast of 3 ohms to 24v should emulate starting mode.

Have fun,

Alan

[chacaocop1]

Alan:

Needless to say your reply was extremely educational. I was not aware of the 3 ohm "rule" that makes the voltage drop (basic Ohm law) in order to have the right spark for the truck. I thought the wiring was different for every voltage 6,12 and 24 Volts, I did not know that the coil wiring was pretty much the same except for the internal balast resistor.

Correct me if I am wrong, but according to my limited knowledge, the hotter spark means that the "arch" generated will be more powerful creating a bigger electrical discharge and as a consequence burning more gasoline in a shorter time giving more power to the engine. Even the EPA does not mind bigger coils since the gasoline will burn better.

I remember once when my alternator main cable got loose in a mustang I used to own and when I realized it, the battery was very low on voltage and the car had very little power. As soon as I tied the cable back, the car regained the power almost instantaneously, making me assume that the bigger (hotter) the spark the more powerful the car could be.

But now I have a question for you. I have read many ads for VW hotter spark coils, etc and has always been interested in applying it to my pinz.

Have you ever tried installing a pertronix HV coil in a Pinz? Can I assume that my assumption is correct and my Pinz will run better with it?

http://www.jegs.com/p/Pertronix/Pertron ... 5/10002/-1

[pinzinator]

Alan, are you saying that a 12 volt Bosch blue coil will work on a 24 volt Pinzgauer as long as the primary resistance is 3 ohms? At which 2 points do you measure the resistance?
I always viewed a coil as a high frequency transformer, not much different from the transformers used by utilities, which operate on a fixed 60hz and a windings ratio of 30-1 (although that may vary).

[pinztrek]

Lot's of good questions, skip if not interested!

I was not aware of the 3 ohm "rule" that makes the voltage drop (basic Ohm law) in order to have the right spark for the truck.

Yep, that's it. 12-14v in a 3 ohm coil primary is 4-5 Amps. whether fed with 24v and a dropping resistor or 12v without, it's still the same coil current in the inductor, which will yield the same magnetic field to the transformer. And thus spark.

Correct me if I am wrong, but according to my limited knowledge, the hotter spark means that the "arch" generated will be more powerful creating a bigger electrical discharge and as a consequence burning more gasoline in a shorter time giving more power to the engine. Even the EPA does not mind bigger coils since the gasoline will burn better.

Like most things in automotive performance, this is true only to the extent that you are removing a constraint.

Otherwise we'd all have giant coils on our cars.

Clearly a weak spark results in incomplete combustion, or no combustion at all. So hotter spark rarely hurts unless you carry it too far.

But you reach a point when diminishing returns kicks in. Hotter spark does not return improved results to justify the expense.

If it did, we'd all run super hot coils by default. Mfg's clearly know how to do it, and in fact usually temporarily make the spark hotter for cranking by bypassing the ballast.

But now I have a question for you. I have read many ads for VW hotter spark coils, etc and has always been interested in applying it to my pinz.

Have you ever tried installing a pertronix HV coil in a Pinz? Can I assume that my assumption is correct and my Pinz will run better with it?

This was a really big deal in 6v vehicle days. In 12v later days the bosch blue was the "hot" upgrade, and the pinz effectively has that stock.

Some of this is system voltage related in the sense that coil primary voltage could sag a bit with small alternators & heavy electrical loads. Or at low RPM. My pinz coil problem way back was at idle, ran fine at speed. But the spark was blowing out at idle due to lower primary voltage.

The flamethrower concept is similar to the bosch blue, and they have models that carry it further.

There are two ways to get hotter spark on kettering point systems:

- More efficient coil: Same resistance (and thus same current), but with larger wire (lower resistance). Which allows more windings, more magnetic flux transfers across the transformer, and you get hotter spark. Sometimes they increase the turns ratio in the transformer, creating more voltage since they have more current.

Decrease coil resistance: the poor man's approach is to lower the coil resistance, allowing more current. But putting more stress on the ballast resistor (heat) and switch/relays. Some systems can handle it, others are more borderline. Or you can just not use a ballast resistor. You'll see some coil heating due to the prolonged current. But works OK for a short race.

In points days the coil current directly impacted points life. With devices like the pertronix or other electronic points replacements, this is less of an issue.

Coil heating comes from the internal resistance. Bigger wires == lower resistance == more current without heating == hotter spark

So the $60-70 Pertronix coil is the extreme upper end of the coil. Big wires, more efficient, etc. Available in standard coil resistances, which is good.

The cheaper flamethrowers are more like the bosch blue. Better than a plain stock coil. Some folks put the lower resistance ones on, which is a typical race thing, but system life will suffer.

Myself, I found the bosch blue true 3 ohm coil to make a bright blue, fat spark. Noticably better. And cost me every bit of $24 at my local VW specialist.

Caveat:

1) All of the above changes a bit with resistor plugs, and or resistor wires. The normal bosch ignition can handle one or the other, but not both. Bosch platinums pretty much come only in resistor form, and there are zillions of posting of folks who badmouth bosch platinums. What it really is that they are using resistor plugs with resistor wires, and the normal coil just is not hot enough. Use one or the other! Modern cars go super high voltage to allow both resistor plugs & wires for interference reasons. Also idle emissions, etc.

2) Plug heat range has an effect. Jake & others know far more about this then I ever will, but you can get too much spark/heat and run into problems. Hard to do with points systems, but it can happen.

Net-net: a $25-35 bosch blue or normal flamethrower combined with civy dist/wire conversion is a big win on pinz's. I'm not sure I'd spend $70 on the super flamethrower until I did that and found it wanting.

And of course, distributorless is the biggest win!

Have fun,

Alan

[pinztrek]

Alan, are you saying that a 12 volt Bosch blue coil will work on a 24 volt Pinzgauer as long as the primary resistance is 3 ohms?

Yes, electrically identical to the pinz coil with military connections.

At which 2 points do you measure the resistance?

What I'd call the "primary". It will be the "+" symbol and the other low voltage coil. (may be labeled "-"). It's the one that goes to the points.

I always viewed a coil as a high frequency transformer, not much different from the transformers used by utilities, which operate on a fixed 60hz and a windings ratio of 30-1 (although that may vary).

OK, more semi-technical stuff:

Coils as used in kettering points systems are specialized forms of a transformer. Not really used with AC, but does step up voltage just like power transformers do.

This link has some nice diagrams of bosch setups:
http://bmwvmca.org/joomla/index.php?opt ... &Itemid=37

When the points are closed, DC flows through the coil and essentially charges up a magnetic field in the coil. since it's DC, nothing jumps across the transformer yet.

But when the points open ("break"), the coil primary does what inductors do. It tries to keep the current the same, and the magnetic field collapses. Voltage goes way up in the coil temporarily, and that changing voltage does trigger the transformer effect (it's like temporary AC in a way), and the transformer windings step that voltage up thousands of time. Enough to jump the gap in the plug creating the spark.

Now the voltage oscillates (bounces) a bit, which would cause arc'ing across the points. That's where the cap (condenser) comes into play. it smooths that out, canceling out the inductance of the coil as far as AC voltage goes.

The pertronix ignitor replaces the points with a transistor switch, which does not arc/wear. It's a big win.

Assuming your ballast resistor/supressor/ignition switch is OK, delivering full voltage to the primary the coil & points should do their job. From there, you can look for a more efficient coil. Also your rotor/distributor has a big impact on spark, as do your wires.

One last pinz thing: what most people think is the ballast resistor is actually a noise supressor. And it can absolutely decrease coil voltage if the contacts are dirty or it's bad. Others can tell you more about that, I've been distributorless for too long to remember the specifics.

have fun,

Alan