i have a 1999 gsr and it misfires and only revs up to 4000rpm!!

can sombody help me out.

 

Is your check engine light on ?
Give us all of the specs on the motor setup...
What spark plugs are you running at what gap ?
Do you have a wideband oxygen sensor installed? If so what air fuel ratios are you seeing at what load ?

 

its a stock gsr. idk about anything you just asked me..

and yes my check engine light is on. but my o2 sensor are not connected.

what would make the motor misfire and only rev at 4k rpm

 

whats the specs on the motor
sure its not in limp mode

does it run very rich, blow black smoke,debree

do what he said above

 

This would be called limp mode.

The ecu is not getting a reading from the O2 sensor as it is unplugged, thus the check engine light on the dash. With this, the ecu enters a fault management mode and won't allow the car over a certain rpm as to prevent any possible damage to the motor.