I have a 2000 honda accord f23b automatic and it has a full exhaust from header and back and intake and has had a exhaust leak from manifold and the other day i noticed vtec doesnt kick in when i stomp on the gas and the rev limiter is at 4000 rpms instead of the red line like it use to be and check engine light has been on due to o2 sensors but have not yet checked it for any other codes what could cause this problem and how can i fix it?

 

Check your codes and fix the issues. Your car is in limp mode

 

So i should fix the o2 sensor as well as the code that it would throw? And it like slowly happened to so like every once in a while it would work and at first i thought it was my tranny slipping but i put it in nuetral and reved it up and only went to 4000 rpms but then since i have an exhaust manifold leak i thought it would mess my valves up just like if you ran open headers it would mess up your valves but ill try fixing all the codes

 

Do you have O2 sensors installed? I only ask because you said you knew you had a code for O2 sensors...but didnt know if you had any other codes? The modern fuel injected relies on O2 sensors for just about everything. They are very important.

Also, you can either have a clogged VTEC solenoid...or the solenoid isnt working...or the computer isnt sending a signal to the solenoid...for whetever reason(You can test the VTEC, and the signal going to it) Sorry for the run on sentance

 

Check your oil level as well, low oil = low oil pressure = No VTEC.

 

I had this before. o2 sensor will cause the ecu goes to limp mode. Just replace it and you will be good.

 

Fix your exhaust leak before you go replacing the O2 sensor. A leaky exhaust manifold can create a false lean AFR signal from the O2 sensor.

Fix the leak in your exhaust, reset your ECU and go from there.

 

I have a 99 accord, manual, and my vtec went out as well. Same thing stopped at 4000 Rpms. Threw up code p1259 I think. I replaced the spool valve aka the vtec solenoid. Works fine now