hi there. i recently observe a strange behavior and would like your expertise advice.

scenario 1: while going 60mph at around 2k rpm in 5th gear, i floor it to cause engine hesitation as it moves to 2.5k-3k rpm range. it builds boost but slowly and engine check light is on for few seconds, obd2 diag shows random misfire so could it be spark plug? fuel pump? all 4 spark plug replaced recently, fuel pump pressure at 50.

if I downshift to 3rd gear, floor it and it would build boost fast and send the car flying
if I downshift to 4th gear, floor it and it would build boost slower than 3rd and it also goes fast
I can shift 1st to 2nd and send the car to 65mph without misfire and various shifting gears without error

 

5th gear boost romp is a no-no. 3rd gear at 60mph is gonna see you in boost range RPM, 4500-ish so, yeah, you're gonna sail. 4th gear will be laggy, yeah. Anywho.. 5th gear isn't liking what you're asking it to do.. Stop it!! Lol!

 

so who cares about random misfire right? it's bad to put on high gear to spool anyway like u said.

 

Based on the info you've given, it is misfiring in 5th when you're trying to goose it.

 

It is likely that the tune isn't spot on at the place in the fuel/timing maps that you are working from when you are at low RPM in 5th gear. For a quicker spool, it is always better to select a lower gear instead of lugging the engine in top gear. ALL cars will accelerate faster in lower gears... so if you are trying to accelerate fast, choose a lower gear.