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I am experiencing misfiring under boost which has improved with the spark plug gap reduced to 0.9mm from the standard 1.1mm.
Has anybody run the standard NB8A coils at 12psi or more?
The NB8A has transisterised twin fire (wasted spark) coils mounted at the back of the rockercover. The NB8B had similiar coils mounted to the top of the rockercover. The SP and SE models used the NB8B coil setup.
Has anybody had a misfire and found a better coil to fix the problem?

I would recommend going over to a COPs setup. They are very easy to make. Source some Toyota coils, part number 90919-02239.

http://www.miataturbo.net/showthread.php?t=12704

I'd second the COPs suggestion.
I went through 3 std coil packs on my NB8A in under 12 months. (The original set and 2 brand new ones)
And mine only gets dríven once a month (on the track) so that was prob only 2000km max.

Bought a second hand set of Corolla COPs from the wreckers for $120.
A few hours with some wire and a soldering iron (and I'm not even half useful with one) and I havent looked back.
All up cost was around $150.

Dean at Motorsport Essentials changed Cookie's car over to COPs as well to fix the same issue you are experiencing.

Rascal, were either of those setups on the OEM ecu?

If so, how are they? runs the same as stock?

Any idea on the longevity of the new coils?

hks_kansei wrote:Rascal, were either of those setups on the OEM ecu?

If so, how are they? runs the same as stock?

Any idea on the longevity of the new coils?

I'm not too familiar with the NB/NA8 dwell times but from memory the stock time was about 3.5ms. Toyota COPs want 2.2ms ish dwell times. You'd want some sort of dwell adjustment to run them on the stock ECU, there's a schematic on Miataturbo or Miata.net somewhere for the PCB map.

Running them with a higher than ideal dwell time and they'll overheat and burn out causing problems like misfires and eventually lead to the death of the coils.

As the stock ECU runs wasted spark, there are only two output signal wires. To run coil on plug, 4 signals are required at half the frequency.
The piggy back processor I am running does not have the ability to do this conversion. Has anybody run the 4 COP coils in a waisted spark configeration (ie. firing twice per cycle)?

Everybody does.

A few people making big power on my cops setups which works exactly like this, you just run 2.5ms dwell on run and 4.5ms on cranking.

Dann

Thankyou for your help.

hks_kansei wrote:Rascal, were either of those setups on the OEM ecu?

If so, how are they? runs the same as stock?

Any idea on the longevity of the new coils?

Both mine and Cookies run piggybacks so can set dwell easily there. Factory is 5 ms. Change this to 2.5ms as mentioned above.
If using a std ECU then you just need a dwell adjuster circuit to do the same. miata.net has plenty of posts on how to do this.

We also run a 10uF capacitor between 12v and ground to ensure the coils see the full 12v. Without it you only see about 8.5v from the std wiring which does mean you can run them like this on the std ECU without the dwell change, as they dont get enough charge inbetween cycles to burn out. Personally I'd make sure and change the dwell, but Cookie did run one meeting at 5ms and the capacitor disconnected with no issue.

As stated above, I went through 3 orig coils in 12 mths, and have now had the COPs on for nearly 12 mths with zero issues.
They're very reliable units. Several on the big forum have had them on for years without issues.

The piggyback processor I am running also allows adjustment of the dwell, although I don't know if it can differentiate between crank and run.
I should be able to make a neat jumper loom for the Corrola coils using the connectors from an old NB8a coil set that blew.

Did you also measure 8.5v when running the standard MX5 coils?

if you can adjust dwell,then its a no brainer to go cops,plenty of places to find them,heres one(unrelated to me)

http://www.ebay.com/itm/280869609211?ss ... 1423.l2661

I had them on my standard ecu NA6 since august (very well made by Dann)

viewtopic.php?f=57&t=47747&hilit=cops&start=165

no real problems except for a slight miss around 3300 -3600 rpm which disappeared when i fitted 2 x 4700 capacitors (all I had that was suitable at home) they were getting hot,not sure how hot they usually get,but was prepared to put up with a possible shorter life until I made up a dwell reducer board.(lazy me).
had 11 ish volts running without caps and 13.5 ish with.miss dissappeared after fitting caps,and ran good for about 8 weeks until i accidentally killed 2 coils by carelessly mangling a connector while playing with timing.
Mick

Thankyou for the info.
The Ebay link saved me the time to find some coils and leads. $99 for new parts seems like good value to me.

Unfortunately, the piggy back processor I am using does not allow dwell control in the opperating modes that do not cause other issues. I should have checked this before buying the coils, making mounting brackets and making a jumper loom.
I eventually found the thread in Miata.net about a dwell adjuster circuit but the diagram was no longer attached. There was also talk of avaialability of some of the parts and the addition of transistors later in the thread.
Does anybody have a circuit diagram of a dwell controller that they know works? Alternatively, does anybody know of a cheep dwell adjuster?

There's this thread in miataturbo which does still have the diagrams. http://www.miataturbo.net/showthread.php?t=19780

Jaycar produces this kit which claims to do dwell control from the 5V ECU trigger signals (among other things).
http://www.jaycar.com.au/productView.asp?ID=KC5442
Haven't tried it myself though cos I already have timing control from my ECU and don't see enough value at $72 for just dwell.

manga_blue wrote:There's this thread in miataturbo which does still have the diagrams. http://www.miataturbo.net/showthread.php?t=19780

Jaycar produces this kit which claims to do dwell control from the 5V ECU trigger signals (among other things).
http://www.jaycar.com.au/productView.asp?ID=KC5442
Haven't tried it myself though cos I already have timing control from my ECU and don't see enough value at $72 for just dwell.

It says:

Suitable for single coil systems

Does this mean it won't work on an MX5?

Or even worse, an MX5 would need one fro each coil? (Costing $280)