So I recently got a 1995 usdm gsr B18C1 swap into my 993 Honda Civic Si Hatchback. I bought this motor from my friend and he let me test drive the his car that had the b18 and it was driving really nice, so I took his offer. So on the first day my car drove great, but the second day it was running like crap. The car began to idle weird and acceleration felt like it was lagging. I took my car to the guy who did my swap and we began looking for the problems and also my forgot to mention that the motor has itr pistons

List of things that were checked/changed by mechanic:
-Checked for vacuum leaks
-Checked the dizzy, caps, and rotors,
-Checked spark plugs and wires
-Changed the ect sensor (touching wires)
-Adjusted idle valve screw (accordingly)
-Adjusted tps (accordingly
-Adjusted timing (accordingly)
-Check fuel pressure (stock D16Z6 Fuel pump)
-Check for clogged fuel lines
-Checked and used other p72 ecus'
-Changed valve cover gasket and seals

My mechanic suggested that I change the D16Z6 fuel pump to a gsr fuel pump to see if that's the problem, but I'm scared that it won't fix them. All these things we did and the car still runs the same.

Things I replaced:
-Changed fuel filter
-Changed the iacv
-Changed the spark plugs (ngk V-power)
-Bleed the coolant for any possible air bubbles

still no improvement after all this

I really need help figuring out what the problem(s) could be and would appreciate any kind of help.

Here are the things on my car:
-2.5 inch custom exhaust piping with magnaflow muffler
-K&N intake
-D16Z6 catalytic converter
-LS headers (friend didn't have gsr headers)
-itr pistons

 

Fuel pump won't do anything unless your fuel pump is going out. My vx fuel pump which has a lower flow rate than the z6 and worked fine on my gsr swap.

Have you done a compression test? Stock p72? That could be a problem due to higher compression of ITR pistons.

 

Opps forgot to mention that.
All compression on each cylinder was good and running on stock ecu.
So if it could be the itr pistons due to high compression, what can I do to find a solution.

Also, I was planning on getting the motor bar'd, but now I don't think I'll pass anyway because of the itr pistons.