cruiser

^^^ Maybe you didnt read it carefully ?

David Beale

Let's see if I can explain ignition system limitations (to non-electronics guys ).

If you've ever used a "spark plug cleaner/tester", you will know that as the combustion chamber pressure rises, it gets more difficult to get the spark to jump across the plug gap. The reason is the gas in the gap is an insulator. If you stuff more molecules in there (higher pressure) you need a higher voltage to jump the gap. It isn't resistance like in a resistor - it's ionization resistance. The voltage has to ionize the gas in the gap to jump it.

So, if you raise the boost you are also raising the pressure in the combustion chamber and you need higher voltage to jump the spark plug gap. You can reduce the gap but this is just a compromise - the shorter spark will have less chance of igniting the mixture, so very quickly you will run into the same problem - missing.

Coils do wear out. They will often show the proper resistance, but they will start to "break down" internally. What this means is at some voltage level the energy will flow through the internal insulating material, effectively acting like a short and absorbing the energy you need to produce a spark. When the combustion chamber is at low pressure the spark will jump the spark plug gap at a voltage that is not high enough to flow inside the coil. The voltage appears to us to rise immediatly to its' max. value, but it actually takes up to a few milliseconds, and halfway to the voltage levels you need something starts to break down.

You can test the coil for this out of the car. You will need a short length of ignition wire, an adjustable spark gap, and a small battery to use to energize the coil. Don't try this with coils that have electronics in them (such as the RX-8 coils) unless you know what you're doing. You can calculate what voltage the coil breaks down at because you know that it takes about 15-20 kV to jump one inch in free air (15 PSI absolute). You will need a good wire boot at the coil output and direct (straight) ground cable between the coil and the other end of the spark gap. Watch your fingers!!! When you spark the primary even it will generate around 400 V! You can also use a hair dryer to heat the coil up to see if that is what is making it fail.

This breakdown can also apply to the ignition wires/boots. When the voltage gets high enough it will flow through the insulation or around the boots (around the boots is very common, even on an RX-7).

Bottom line is, if you want to run high boost you need an ignition system in good working order - that is, capable of generating very high voltages without breaking down. A good example of the extreme limit to this is the ignition systems they use on AA Fuel class cars. High boost and lots of fuel needs very high voltages. Have a look at them and you'll see what direction you want to go in. You don't need what they use, just more of what they have than you have now.

Kento

I have never heard of modern ignition coils' internal insulation "breaking down" and allowing voltage to basically leak-- but obviously that doesn't mean it's not possible. I have heard of the windings breaking, but only in very old coils (when that happens, the winding will have contact when the coil is cold, but when it heats up, the internals expand and the winding separates).

David Beale

How old are you? I've had coils that did this, (motorcycle ones coincidentally, as well as auto ones), I've had coils that arced in the windings, I've had coils that had breaks in the internal connections as you mention, ones that were shorted internally, and I've had coils that melted (but they were easy to diagnose . One of the motorcycle ones caused me to start doing my own testing - the local Yamaha dealership had a very expensive "coil tester" that said it was fine. Funny how it constantly failed on me. Funny how when I changed it out it fixed the problem. I was able to confirm its' poor condition with the above mentioned testing procedure.

Yeah, I'm old. Much of my experience was gained in "the old days", carburated engines with points for ignition. I started building my own electronic ignition systems, including capacitor discharge. When you overpower the ignition coil you can induce amazing failures. These days you can buy coils that can take that kind of abuse.

Kento

Well, no offense, but I guess that is pretty old . That's why I said "modern" ignition coils. I raced motorcycles in amateur, semi-pro, and AMA pro competition for 18 years on a myriad number of machines, and never had a coil failure. And many of the machines I rode had high compression ratios with 120 octane leaded racing fuel, requiring some serious ignition modifications.

That said, when the coils become overloaded continuously because of poor maintenance (extremely worn plugs, plug wires, bad grounds, poor tuning, etc.), they can fail over time. But in my opinion, that is rare, especially with a car like the FD that cannot survive such abuse without something else causing major problems before that happens.

David Beale

True, coil failure is now rare. I think some of my problems were caused by temp extremes - here in Edmonton Alberta the temp will go as low as -50C and as high as +40C (and my vehicles, even though only stored and not driven in winter are exposed to the lows and are exposed to the highs in summer while being driven). All should realise that the FD coils we have in our cars are now at least 10 years old (in North America, anyway), and have been exposed to very high temps.

Oh, and no offense taken. Proud to have survived so long while driving performance vehicles!

KevinW

iTrader: (1)

i'm going with 4 LS1 coils, they have individual ignitors built in to each of them and brand new only around 60.00 each. the falken drift car uses these with no amp and they have great results

KevinW

iTrader: (1)

oh they also run more than 15 lbs of boost on the GT35R i believe

dgeesaman

iTrader: (7)

I dug this up when reading about ignition problems, and felt this could be clarified.

Kento's statement is true for coils that are in air, without insulation.

When dealing with high voltage components, the magnitude of the voltage is always a factor. Since I don't have any info on ignition coils, I just estimated that since it produces a spark that can jump 1/4" to ground (as per the normal spark test), that's about 19kV. 19kV is enough to see high-voltage effects such as corona and surface tracking. A multimeter testing resistance is much lower and can only detect shorts or opens in the copper coil - it cannot test insulation integrity.

Turn-to-turn insulation can break down - and the air pocket left between the coil turns will spark over at a much lower voltage than they should. Usually it's a steady degradation that increases in speed as the breakdown increases. So the resulting spark at the plug gets continually weaker. But the multimeter won't read it since it doesn't have enough voltage to jump the air and short circuit.

Dave

TwinTurbo93

You should't have ignition brake-up running 12-14psi or even a bit higher psi, I suggest you check the coils.

I had a coil crack in the middle, see this thread for more deatails, which caused pretty bad hessitation or ign. brake-up of some sort @ around 4- 5.5k rpm.

When I replaced the coil, I did few 18psi runs with no ignition brake-up of any kind.

89t295k

Good info....I too have been pestered by ignition break up/detonation running a very conservative mix of mid 10 afrs and low 12-13 advance at 12-15 psi.

After a few runs it starts to lose power up top and scatters the rpm readings on the haltec.
After looking at my dyno charts from the last few years it would seam as if the line would go violently up and down on various engines/turbos/mods uasually at 7k plus and go lower with more abuse.

I figured it was a week ignition/plug/wires but, everybody says T2 stockers don't fail???

So I put on accel wires, put fresh 9's in the leadings and it got a bit better but, still feels crappy after 6500.

Looks like I'll b questioning the stock ignition too.
Any recomendations for testing the T2's coils or should I just replace/amplify them?