Loud "Pop" Options

[GuYun14]

Hello everyone,
I have a 1998 Celica GT auto with the 5sfe engine and I was merging on the highway so I decided to floor it but when it got to the 4000 rpm I heard a loud "pop" from the engine bay. Sounds like it came from the intake. Plus, it wouldn't shift and seem like it was hitting the rev limiter. So I wanted to see if anyone can help me with that.

Mods: Injen short ram intake and custom 2.25 exhaust.

[GuYun14]

This may have happened for several different reasons:
Timing
Timing belt issue
Weak fuel pump
Low fuel pressure
Incorrect air/fuel ratio
Bad catalytic converter
Bad or cracked spark plug
Bad injector(s)
If it was my situation i would do all the inexpensive things first:
Check fuel pressure at speed and hi rpm
Check spark plugs for cracked porcelin and gap
How old is the timing belt

As stated before, when I did my fuel filter I kinda twisted the fuel line a little bit but this issue was happening before I did it. So I doubt that was the main problem from the start. And when I got my custom exhaust I also got a new catalytic converter put in but I've had this issue before all that. I might have the check everything again like you stated. When the new motor got put in I just assumed that they replaced everything so I don't really know if it's old or new or if it was replaced at all. The mechanic seem kinda shady to me. But thanks for the tips.

Well if you have to redo timing it's somewhat involved, here's a writeup for the MR2 but it's still a 5S so everything pertaining to the engine itself will be the same: http://bobaab.awardspace.com/timingbelt/timingbelt.html

Thanks! I also remember seeing a video on Youtube about changing the timing belt on a 5sfe so I might look for that too.