Misfire/backfire/knock @ 4000rpm's

Hello there, i've been running gently my fj20e after a minor parts replacement like bearings and rings...
I've done almost 800km's on the engine under 4000-5000 rpm's ( not me was driving...), so now when i start the car in the morning, it's ok, there's nothing wrong with the engine,@ normal operating temperature and revs freely till redline, but when warmed up in the afternoon, i can't fully open the throttle because @ approx 4000rpm it starts to backfire,knock, feels like a rev limiter, but if i step gently on the gas, it climbs higher, i,e to 5000rpm's... ( the coil is strong , a bmw 740 one, had it for 5 months..)
I've checked the plugs, they're very good,brownish/red/orange color and are dry and even replaced them, but the problem persists, checked the distributor timing and adjusted it with a gun ( a stroboscope like gun...), the wires are ok, fuel pressure also ok...
I dunno, i'm getting frustrated, i looked @ almost everything, even a mechanic checked it and couldn't find the problem, because if the car cools for about 30min, the problem disappears, and later on it reappears...
But i installed a nismo intake cam 288 deg duration and 10.5mm lift, is this the problem, does the ecu need remapping for the cam? but there's nothing in the morning...
I posted the problem on the fj forum but with no replies...
Any help will be very much appreciated

DochkaHello there, i've been running gently my fj20e after a minor parts replacement like bearings and rings...
I've done almost 800km's on the engine under 4000-5000 rpm's ( not me was driving...), so now when i start the car in the morning, it's ok, there's nothing wrong with the engine,@ normal operating temperature and revs freely till redline, but when warmed up in the afternoon, i can't fully open the throttle because @ approx 4000rpm it starts to backfire,knock, feels like a rev limiter, but if i step gently on the gas, it climbs higher, i,e to 5000rpm's... ( the coil is strong , a bmw 740 one, had it for 5 months..)
I've checked the plugs, they're very good,brownish/red/orange color and are dry and even replaced them, but the problem persists, checked the distributor timing and adjusted it with a gun ( a stroboscope like gun...), the wires are ok, fuel pressure also ok...
I dunno, i'm getting frustrated, i looked @ almost everything, even a mechanic checked it and couldn't find the problem, because if the car cools for about 30min, the problem disappears, and later on it reappears...
But i installed a nismo intake cam 288 deg duration and 10.5mm lift, is this the problem, does the ecu need remapping for the cam? but there's nothing in the morning...
I posted the problem on the fj forum but with no replies...
Any help will be very much appreciated