Constant coil-pack failure, especially after CNG install

First off, I'd like to say hello to everyone on here on the Bajan Autos forum, especially as it's my first time posting. So...

Hello everyone!

So, I'm hoping someone could possibly help me with a problem I'm having with my Serena 7-seater. I should mention it still got an MR20 engine in it, though not the original one it came with. The problem I'm having is with the coil-packs, I keep having to change them constantly, even though It's hardly ever driven.

Recently I installed a CNG kit, this seems to have made the issue even worse, as I've come to learn that CNG apparently, is more demanding of coil-packs, and even spark plugs. I've just installed four brand new OEM coil-packs. It drove wonderfully on the way home, didn't use the mini-van the next day. I notice a slight momentary stutter with the engine, eventually the check-engine light came on, and the stutter became progressively more pronounced.

I've seen this all before, and I'm dead sure, it's the coil-pack or packs again. Tomorrow I'm heading down to the mechanic to confirm, what I believe I already know. I was even told by a technician NOT to install brand new OEM coil-packs, as this exact thing would likely happen. It would fail the next day. But to get them foreign used, as this was his own experience with Serena vehicles.

He was obviously RIGHT!!

So more to the point, my question is about what could possibly be responsible for this constant coil-pack failure? I've heard of heat and faulty spark plugs. However, at no time the temp gauge went above its normal position. After the CNG install, it possibly increased by one bar - I'm not sure though. But I believe I can physically detect that my engine's running considerably hotter, when running CNG, whenever I open the hood to refill. And I think I was told that CNG does in fact run hotter by the technicians.

As far as spark plugs go, I changed them earlier this year, and as I mentioned before, I hardly even drove the van since. If anyone's got any recommendations regarding sark-plugs, brands or specs, I'd be glad to have them, along with any other suggestions regarding this issue.

Thanks!