I have had the stock ignition coil over plugs (COPs) failed twice now. Once on the dyno and Toby got second hand replacements. The second time when I was back in Penang. Every time this happens the Shark sounded like a Subaru Impreza WRX wannabee minus the power as the engine was only running on three cylinders. Imagine not being able to exceed 2000rpm in fourth with a top speed of 60km/h :(
The QG18DE runs a distributorless ignition coil over plug setup which Nissan calls NDIS or Nissan Direct Ignition System. This means that the ignition signal is directly sent from the ECU to the inductive ignition COPs which are responsible for igniting/firing the spark plugs. The signal is carried via three very thin wires so don't bother about fatter spark plug cables because a direct ignition system does NOT USE ONE. The COPs that come with all MYDM Nissan Sentra N16s with Series 1 QG15, 16 and 18DEs are of the pencil coil type and are made by Hitachi. Pencil coils have a compact "head" because the coil's magnetic windings are all located in the tube that forms the length of the coil. This results in a neater sleeker looking cylinder head top.
Picture below of the stock Hitachi pencil coils installed.
To date I am not sure why the stock coils are failing on my engine. It could be due to one or a combination of two reasons:
1. A much hotter turbocharged engine/engine bay. Having the coil windings deep into a much hotter engine ain't gonna help and pencil coils are notoriously prone to failing because of this.
2. The ECU will know in advance when it wants the spark from the coil. The target is to start the dwell period (coil charging time) enough in advance of spark event for the primary coil current to reach full energy storage. On a stock engine with stock compression this is not a problem. However a turbocharged engine results in higher cylinder pressure and is more difficult to ignite. A common trick if you are running a programmable ECU like the Autronic SM4 is to increase the dwell period so that the coils have sufficient charge but I believe the dwell tolerance of the stock coils is crap. Increasing it just eventually burns out the windings in the coil creating a short in the circuit. The dwell period is reduced in my Autronic ECU to a very low 2 milliseconds. Anything less and there will not be sufficient charge to ignite the combustion mixture when Sharkie is on boost. Dwell is controlled via software for the SM4.
I believe Nissan also realized this and went for a conventional coil on top of plug type COP on later Series 1 QGs and eventually becoming standard on Series 2 QGs which never made it to Bolehland. The newer coils have the windings in the head versus the tube. Every centimetre farther away from the heat helps. Illustration extracted from Hitachi's website shows both type of ignition COPs.
Picture below of my stock and "newer" ignition coils. Stock COP is at the bottom. Both fits your QG.
Disregard the perspective from my camera making the stock coil appear bigger than the newer type coil. Here's a picture with the newer coil at the bottom if you don't believe me.
I am currently testing the "newer" type COPs which are from the engine I bought. The coils look like crap externally but the important parts inside are in good nick and seem to be holding out fine at this point. A brand new set of 4 newer type ignition coils will be around RM 1.1K-1.3K original Nissan without shipping depending if you purchase from Greg or my Jap supplier Nakahara-san. Picture of the newer type COPs installed. Kinda reminds me of the stock pencil coils being fed the same gamma ray as what turns Bruce Banner into the Incredible Hulk.
The original part number of the newer type COP - 22448-6N001. These are made by Hanshin which is a subsidary of Hitachi. 22448-6N000 is also used. Hitachi's excellent website lists compatible coils. Nissan also uses another oem supplier for JDM QG10 Bluebird Sylphys. The other supplier is Bosch. I am not sure if Bosch COPs fit as I have yet to get my hands on one.
22448-6N001 has been superseeded by 22448-6N015. Use this part number if you have the intention to order some new ones for testing. Below is the part number of all MYDM N16 COPs - 22448-4M500. It's like our N16s are caught in a time warp and have never progressed beyond first gen apart from looks :( I think this is a common Bolehland issue as another example would be the Toyota Camry for its engine and gearbox. If it makes you feel better 22448-6N015 is also used by the Latio/Tiida with HR15/16 engine if I'm not mistaken.
So what is my upgrade plan? I am going to persevere with the newer type stock COPs for the moment as all my upgrade options are expensive and I'm still undecided if to retain the stock inductive ignition or go CDI. More research required. Of course if the newer type COPs also fail prematurely (touch wood) it will then force the decision. Will see how things play out.