Ignition Coil Spark Voltage

from: https://rivperformance.editboard.com/series-ii-engine-transmission-f4/car-trouble-t6705-15.htm#99149

GMFreak8 wrote:

A bad coil pack could cause an issue similar to this too, especially considering the coil packs on these put out two different stages of power, the second being when you step on it....

Just where is the info on the "2 speed coils".
I've never actually seen it in any FSM, only mentioned on here.
The coils fire a cylinder that is on the compression stroke and a dead spark on it's opposing cylinder during it's exhaust stroke simultaneously. (known as dual fire coils)
The coil does not not have two output voltages, just more output available to the cylinder on the compression stroke as the opposing cylinder's exhaust stroke does not offer any resistance.
There is no coil made that I'm aware of that can possibly put out more secondary voltage as you put your foot into it.
This is partially why the OEM's went to "Single Fire Coils" or coil over plug ignition systems, to better control the amount of current being supplied at any individual spark plug at the exact appropriate time.

The problems that are encountered during heavy acceleration or high load and experience low power are either bad ignition wires, fouled plugs, poor coil connections or a bad coil.
Very rarely will you find multiple coils gone bad at the same time. Usually it's a bad connection such as a ground wire. Or as Matt has shown brittle and broken wires at the harness or elsewhere. These cars are now old enough to experience brittle, dry, cracked wire insulation and shorts or completely broken wires from vibration or from upsetting a harness by moving it around to replace a component.
That is why when replacing either the Crank Position Sensor (CKP) or the Cam Position Sensor you must pay particular attention to the wiring harness's and their condition when you are finished.

Rick, very good question, and a valid concern that needs to be addressed. I had always been under the impression that our PCMs delivered a higher voltage spark when in boost (under high load conditions). This was seemingly proven to me by members of INTENSE Racing staff a few years ago when I visited them with a pulsating miss that only occurred under boost. It turns out there is a higher voltage delivered under boost, but I don't believe the PCM commands it.

When I went to have my problem diagnosed, they were at first perplexed, but soon determined the miss was only happening when in boost, and so concluded it was ignition related. After removing the SC belt, we found the miss went away, supporting our conclusion. This narrowed down the problem to the wires, since the plugs were fresh. Sure enough, the wires were not able to flow voltage under boost, but were fine operating up to atmospheric pressure. Replaced them and problem solved.

Since that day, I was always under the impression that spark voltage was higher under boost than when not. I am not 100% sure, but I think I know the answer, after reading up on the subject of coils and spark. It would seem that an ignition coil does not always output its fully rated secondary voltage, but only just enough needed to bridge the spark plug gap, and that amount is constantly changing depending on engine load/boost. So in a sense, secondary voltage is dependent upon MAP.

When operating in vacuum, the density of air in the cylinders (between the plug's electrodes) is low, allowing a spark to occur at a lower voltage (maybe 10k-15kV), but when load is increased, and boost builds, the required voltage to bridge the gap increases, requiring a hotter spark of 20k-30kV or more. And the coil delivers it, because the denser air offers higher resistance, and so requires hotter spark. I think our OEM coils can hit 40kV if needed.

Here is a link that I think supports this idea: http://www.acuravigorclub.com/Timely-Topics/Timely1104-2.htm

I think this way of thinking supports the reasoning for decreasing plug gap and/or increasing spark voltage for very high boost levels, as their is a need to decrease the resistance between the electrodes, or else the demand on the coil will be too high. Also, this substantiates why worn plugs or wires can weaken or burn out a coil, since the coil would work harder to produce the extra voltage needed to operate under those conditions.

Over the years, I think this whole idea metamorphosed into a new idea that the PCM just kicked in with a higher spark when under boost. I even convinced myself that was the case, but I now think that the PCM doesn't need to do anything at all - it just happens naturally. Thanks for pointing this out, Rick. If anyone with greater electrical knowledge can agree or disagree, please post your thoughts. I'd like to know once and for all if this line of thinking is correct, or if there's some other reasoning behind it.

AA wrote:

Rick, very good question,

Not to be cocky or 'know it all' but it is just Fact as to how a coil works. Not a Question.!!!
The PCM does not provide a higher voltage spark, only a ground signal to to the Ignition Control Module that initiates spark (Dwell).
I am familiar with ignition systems such as 'dual fire' coils, the ones installed in our cars, with a wasted spark in the exhaust stroke of the opposing cylinder and "Single fire' Ignition systems that fire only the spark plug when needed during the compression stroke.
And either of them are capable of putting out 40Kv during the compression stroke for maximum combustion.
If anything in the circuit, be it a wire, plug or ground is bad, then you will get less Potential (voltage) from the coil. And a weaker spark. Period.

I agree with both Rick and Aaron.

Not to mention the fact that terms like "dual fire" may be one of the reasons that this myth got started...

The waste-spark system is nothing more than two terminals on one coil, to save a few bucks when they switched from distributors. As far as 'potential' voltage, the original HEI system 35 years ago was considered by GM to be a "50,000 volt device". The higher voltage that the HEI is capable of was the reason for the wider spacing of the spark plug terminals in those giant distributor caps, and in turn, the 50 and 60 thousandths gaps on the spark plugs. But as previously stated, the 'actual' voltage at firing is whatever is necessary, up TO the rated voltage...

RickW wrote:

Just where is the info on the "2 speed coils".

Actually this is a question, although you forgot the question mark.

Quote :

There is no coil made that I'm aware of that can possibly put out more secondary voltage as you put your foot into it.

Guess I misunderstood you. I thought you were saying that a coil's secondary voltage cannot increase as you apply more throttle. Imo, that is exactly true - increasing throttle puts more load on the engine, and this increases the voltage output from the coils.

not sure this is the right place for this but thought i'd share:

I had a coil die on me about a year or so ago.about a year or so before that a friend of mine with a 97 was having issues and it ended up being a coil as well. Due to the fact that both time you pretty much cant (shouldnt) drive with only 5 cylinders firing we opted to replace them with the first available which was cheap units from autozone (durolast).
Fast forward to last weekend, i was working on said friends 97 and a quick wash down of the motor killed a coil pack, it was indeed the durolast part. Other 2 coils are OEM with 215k miles btw.
It then dawned on me that i still had a less than efficient/performance coil on my car too. So i did some research and found this info from the ssei guys.

http://www.pontiacbonnevilleclub.com/forum/2000-2005-other-than-gxp/topic29036.html

I just ordered 2 of the D576 coils and plan to replace the durolast coils on both our cars. Would it be wise to replace all 3 with the same model coils?

I'd think your OEM coils are the 576s, no? I wouldn't change them if they aren't bad, but I would change the Duralast part. Mine are all original at 258k.

I would think so, but then again they may be a little different since OEM has the numbers on them that the replacement ac delcos do not have.
My main reason for looking this info up is because rockauto always seems to list 1 or 2 different part numbers for AC Delco and normally there is only a $5 or less difference between them. never know which one is the "real" OEM replacement sometimes. I have been going on the assumption that you get what you pay for

Getting ready to hit 200k on them fwiw.

I think you are better off getting a used OEM L67 coil from Morads before any aftermarket new coil. Save some $ too. Coils usually don't go bad.

So are the 576's not as good as a 200k mile OE coil?
Looked to me like the 576's were about the best you could buy, and from what i can tell GM and ZZP both sell the D555 as replacement coils for the L67

The way I read it, D576 are direct OEM replacement for supercharged 3800.

D555 are direct OEM replacement for N/A 3800.

You wouldn't want to buy 555 packs for the same reason you don't want to use standard 3800 ignition wires.

A junk yard OEM pack is basically a used D576. All the other parts listed are lower performing in SC 3800 application, except MSD 8224, which are about the same at higher cost.