The past 5 days.

Friday - Take the car to a potential buyer, runs great pulls hard no problem. I bring the car home and let it go to sleep and I touch NOTHING on it.
Saturday - Take it to DE to show 2 more buyers thinking all is well. I didnt hit vtec once on the way down. The first guy takes it for a spin and comes back saying its missing up top end. So I take it for a spin and sure enough about 5700 it starts to missing and shuddering but keep pulling until it evens out at around 6900. I take it home and let it sit until sunday.
Sunday - I change the oil check the fuel lines and all plugs. Take it out for a test and it still does it. I switch to a milder chip in my ecu and it still does it again.
Monday - I take the car to a buddies house where we, Change the fuel return line, check the pump, turn up the fuel pressure (which made the problem move to 6200 and "miss smoother"). This leads us to aim towards a fuel issue. We pull the plugs and the so that the car is running seriously lean (which we traced to a leaking return line thus low fuel pressure so that solved that.)

SOOOO the game plan for today is to put on a stock fuel pressure regulator thinking maybe my AEM is having issues.
Disconnect the fuel lines and pressure test for blockages.
Switch injectors

Thats all I can think of for fuel, Im not throwing any CELs.

My next thought is spark, I have noticed that around 4500 latley the tach will jump to 5000 as if my ignitor is going, no notice in engine change just the tach.


Any thoughts??? I have 2 people that want the car as soon as I figure out what the hell its issue is. Its the one in my sig to see the mod list.

EDIT: Just switched the injectors and put on the stock FPR and it still did it.... DAMN

 

i would pitch off the return line, this will cause the car to run like cramp at idle and light throttle but it will tell you if the car is running lean up top, if goes away it is definitely fuel problem. maybe coil/ignitor problem