1G Weird backfiring problem (video)

[buhay6]

I'm having problems with major back firing after letting off the throttle, where it be just cruising or coming off of boost. It's done a number on turbo's (been through 4 now) already, it took only 2 weeks to wreck my nicely rebuild 14b from Justin. I do have spiky boost condition's, haven't been able to control it since the port job seeing anywhere from 9-17 PSI, get good afrs cruising. Wideband's installed correctly with factory narrowband deleted.
Current mod's
-ported 14b (not relevant)
-tubular O2 w/g dump (not relevant)
-Innovate MTX L1
-BSE (not relevant)
-fidanza flywheel (not relevant)
-southbend clutch (not relevant)

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Tested/replaced:
BLT (passed, leaky exhaust valve)
Throttle position sensor replaced
Ignition timing checked
coolant temp sensor replaced
spark plugs replaced ( NGK BPR6ES)
Re-calibrated wideband multiple times

Any other suggestions as to what I should look at next? I've checked everything I could find as possible causes but have got no results!

 

[tmoney20g]

what did you change to make this start happening ? non-recirc bov ?

 

[inthemidst]

What about fuel pressure and injectors backfires usually happen and pressure regulator.

 

[buhay6]

Started happening after my throttle body rebuild, everything went for shit after that. So I went back and double check everything was set right, found my TPS sensor was slightly out of spec so I changed that, then found the fast idle control valve was totally gone so I replaced that as well, all new seals etc. I kind of wish now that I hadn't have touched it, car had massive boost leaks but pulled like a boss.

I fixed every boost leak I could find system holds 30 PSI very well only leaks a little passed the piston rings and out a leaky exhaust valve over a few min. Intake and SMIC is completely stock.

 

[buhay6]

What about fuel pressure and injectors backfires usually happen and pressure regulator.

I don't think its an injector failure as I've swapped in 2 different sets already, and it didn't change a thing. I do have a Fuellab FPR sitting on the shelf waiting to be installed so guess it wouldn't hurt to rig it in there for now to see. I have no tools for testing the old regulator tho.

 

[inthemidst]

Did you say you have a leaky exhaust valve well that's the problem. Always fix obvious problems first .

 

[buhay6]

Did you say you have a leaky exhaust valve well that's the problem. Always fix obvious problems first .

It shouldn't cause such excessive backfiring tho, plus all the plugs are sooty. I already know its one of the exhaust valves in cylinder 3 so there should be a difference between the plugs no?
*sigh* i was really hoping to keep from spending another cent on this engine because the thrust bearings totally done.......oh well.
Just did a compression test (engine was still warm to the touch), and got the same comp reading I got when I first installed the engine. also just installed a new set of BPR7ES, as there was some irregularities between the 6ES's I was running

 

[inthemidst]

Do a leak down test so you can see how bad the valve is leaking.