Newly developed Major backfire problem. NOT BOV Related

[BaliLover]

I had to replace a leaky water line to the turbo this weekend, and since then I've been having a problem that was never there before.

I run a tuned Gt2871R turbo at 18psi, but now if I get on the throttle hard in 1st or 2nd, I get major backfiring and stumbling, etc. 3rd gear however, runs perfectly fine, even at 19psi. I am not getting a boost spike in 1st or 2nd, I'm actually not even able to hit my normal boost pressure.

I had hosed the engine bay off to wash off all the coolant that sprayed under there, but I don't know that that would have caused a problem since I clean my engine all the time. I went back and checked all of my plug-in connections just to make sure I didn't somehow loosen one when I was working on it, but they're all tight.

The car runs PERFECT off boost, and perfect during a 3rd gear run. There is no miss at idle, no strange clouds of smoke, nothing. When the water line let go, the temp went up, but didn't make it to the top of the gauge before I shut the car down and made sure that both fans were on. 30 seconds later I cut the key back on and the temp was back down to normal.

Because its not a constant problem, and it doesn't exist in 3rd gear runs, I doubt that there is some sort of internal damage, I'm assuming its a fuel/spark issue. Anyone have a suggestion as to where I should start looking?

[Nismo_Freak]

1. Check timing2. Replace spark plugs / close spark gap3. Check coilpacks

[BaliLover]

Is there any good way to check the coilpacks?