After installing K&N FIPK filter charger kit, I noticed that my car hesitates between 4500-5500 rpm.
The problem does not happen on first gear. or maybe it shifts to fast to notice......
I thought it was the fuel filter so I replaced it and added outlaw fuel injector system cleaner and Mobil premium gas....did not help.

93 Firebird formula Automatic (2.73)
96K miles.
Never replaced the Spark plugs or cables.

Any ideas?

 

Is this a misfire? I would say opti. A high RPM misfire often means a bad opti. COuld verywell be plugs or wires as well. I would change out the whole ignition from the coil on up.

 

you mean right b4 it shifts you get a stutter or backfiring sound? I got that a tiny bit with my intake, and then alot more so with the exhaust (it revs much higher before it shifts w/ these mods). ANYWAY, the most common solution is a coil wire, but could also be plug wires (just get a set for like 35 bucks) . Could also be coil or optispark, or clogged cat

 

Yep this happens just before it shifts but there is no backfire, just slight hesitation or as you put it sttutter.....
In lower RPM's everythings works perfectly.
Again, this only started after replacing the factory filter box with a K&N filter kit.

 

Ditto Kavman.Wires,plugs.(coil wire every 6 months or so.)