2001 f115 turns over then backfires

[train314]

2001 f115 turns over then backfires

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I have changed fuel tank,fuel filter, vst tank filter screen ,needle and seat was very clean, good voltage to fuel pumps plenty of pressure.
I have had the fuel injectors rebuilt and flow tested all are at full 64percent. put it all back together turned the key to prime the system and turned it over engine it grumbled and backfired 1 pop. turned the key again it grumbled and backfired. Now what? hellllpppp

[boats.net]

Check timing belt alignment, check compression and run a leak down test. Check plug wires are on correct cylinders.