HELP! Swapped motor

[Stigmata]

Ok let me start out i have a 92 240sx fastback and i blew my motor due to unknown reasons, mileage was 178k, anways i swapped the motor, direct bolt on with transmission, plugged in the sensors, everything plugged in, i start the engine which is a 95 Ka 50k miles and i start it it idles 900RPM, then i reverse everything is ok, i start driving and i hear a POPPING noise in the engine like some explosion is going on then my rpm drop and the car wants to stall i floor it and it wont go past 3k rps and wants to die again, it starts backfiring and i dont know what i did wrong with the swap, the timing is correct, someone told me it might be the vaccum lines but they are in, o and yea it has a aftermarket cold air intake, S13 Cams and pulley and I am really confused whats going on

[fallen180sx]

sounds like fun.. give it a compression test now

[USDM240]

sounds like a bad MAF sensor to me.

[Stigmata]

Might be because when I took of the harnass I let my dad hold it and he dropped it on the floor on accident. In about 30 mins I will be heading to the junkyard to pick myself a new one, one more thing im not sure where its from, but I think my headers might be leaking, when I tap the car t about 3500RPM smoke comes out threw the headers, might be the gaskets right? THX a bunch for the information

[All_Motor_KA]

Your harness is not going to break just cause you drop it on the floor. All it is is wires and plastic clips. Not too sensitive. Change your header gasket and check for cracks. Does your car still sound the same since before this happened?

[Stigmata]

alright problem solved, i went to the junk yard bought a MAF changed it and car works fine, now another problem encountered, I need a new transmission, its making noises inside eversince I put Mobil 1 Synthetic transmission Lube. Other than that the car runs fine no, but does not pull like the old motor did even that it now has S13 Cams and Pulley