car wont rev past 4k rpms???? help

hello my friend has a 98 accord lx 4 cylinder 2.3 vtec
it has i/h/e 3 piece pulley kit......

car has bout 72k on it..

all the sudden it wont rev past 4k rpms what could cause this?

someone let me know

fuel filter maybe im not sure? let me know ur thoughts....

does he hit a rev limiter at 4k or does it just stop reving at 4k like how if you part throttle and hold the revs at a certain rpm ?

not sure yet... but wat would be the problem if it did hit a limiter at 4k and wat is the problem if it just wont go past 4 but doesnt hit a limiteR?

ECU limp mode? Is he throwing codes?

no engine light.... and he said its like hitting a limiter... but not as bad... and if he downshifts it will go past 4 but no power then it revs down to 4 again.....

check for codes, just because theres no CEL on doesnt mean there isnt a code in the ecu

but are there any other reasons thiis can happend.... besides the ecu?

his car is all stock just i/h/e and pulleys... why would the stock ecu mess up...

I was thinking more along the lines of a sensor malfunction, that may cause the ECU to make the ECU go into limp mode and pretty much make the car a dog. Maybe check the wiring of the vtec solenoid. I'd still think that any way it's throw a code.

so besides the ecu issue... is there any other problems that could cause this to happend.... if so let me know

headgasket

any other things we can check?

My 2k Prelude is experiencing the same problem except at 6500ish rpm. It'll let me pass that number once, maybe twice, but after that it locks me out. I don't really know the problem.

I am throwing a CEL, which I believe is Vtec System Malfunction. I believe it might have something to do with my VAFC changing the VTEC engagement point to 4k. But the car (and VTEC) seem to be working fine. So I'm confused since I've never heard of anyone throwing a CEL for that.

Also I'm experiencing the Cold Air Bypass Valve bouncing idle problem. I don't know if this has anything to do with it.

I'm putting in my OBI ECU and fixing the CABV this weekend. If that doesn't fix the problem I'm gonna start to worry.

can someone tell me where the ecu is located on a 98 accord... please thanks