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Damaged my new engine. The problem with carb to EFI conversion Chevy 434 Swab Nissan Patrol GU

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Project background:

Nissan Patrol GU SWB had the TB42 OEM engine. I Swabbed in a Chevy 434 stroker from United Racing Engines (694 HP package). The engine came with QuickFuel 850CFM carb. The car ran very poor fooling plugs and could not get the mixture right. I had Haltech Elite 2500 on hand so I decided to convert it to EFI for a project:

Haltech Elite 2500

RHS intake manifold

AEM Engine Position Module (EPM) Chevy SBC for trigger (24 tooth for trigger and 1 tooth for sync)

ID1000 injectors

FAST 1350CFM throttle body with IAC and TPS

Wide band O2 control

Load sensing method is TPS. I can't use MAP because the engine very large cam (275/278 LSA 113, lift 0.702). It does make much vacuum, in the range of 25 kPa at idle.

Using timing light, locked timing and set trigger until sync. Started engine and it fired. It kind ran OK but lacks power. ECU threw DTCs regarding sensor reference voltage, P0641, P0643, .....

Temp sensors and TP working fine.

Enabled O2 control self tuning, worked fine targeting my Target AFR table.

Tuned the car on road for some time and then noticed the engine started lacking power and hard t start.

Checked timing, found it drifted idling at 38 deg BTDC, was 21 deg

Adjusted my trigger angle again and sync timing. Worked OK but engine is still weak.

It kept doing the same, timing drifts all over after driving the car even for less than a km.

Changed EPM but did not solve the issue.

I did not have knock control though but I could hear the engine knocking when I was trying to get it run properly.

After a short time the engine started smoking badly.

Contacted Haltech regarding DTCs and they were because the single grounds were joined with Chassis ground. When I cut the connection, DTCs are gone.

Took the engine out of the car to workshop to inspect and found 5 out of 8 pistons are damaged.

Damaged pistons are 1,8,7,2,5 piston 1 is most damaged piston 5 least.

Firing order is 18436572

Any thoughts on what could cause this timing issue?

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