Stumped on misfire/lean mix

[Obi-S. K.]

Hello. 1992 Grand Prix. 3.4L DOHC. 5spd manual. 240k miles.

Im stumped guys .. Recently my fuel pressure regulator went. (Smelt gas, opened throttle body, fuel poured out. Replaced unit, tested OK. Holds/Recieves 41psi) Fuel went through MAP, was all inside intake manifold.

Got the car to run after replacement. However, now it hesitates, misfires, popping coming through intake noise through all my gears. Its driveable, and problem is intermittent when slow accelarating through the gears. Full Throttle punches, the car stumbles all over itself. Seems to mite have a small miss at idle. Seconday AIR pump (smog) whines/ is really loud.

Vaccum lines seem fine. No high idle. No check engine codes. Timing belt is recent. Belt is snug, hasnt skipped teeth.
Replaced/swapped: TPS, MAP, PCV

Im running AC Delco Platinums. Plugs are now coated white (running lean) on all cylinders.

Fuel pressure seems to be good, however only tested during idle and a little revving. Could fuel pump not be able to handle the load? Oxygen sensor giving bad air/fuel signal? Injectors are bad? Bad catalytic converter from when Fuel Pressure Regulator went and sent to much raw fuel?

Im pretty stumped here. Any ideas welcome. Sorry for the long read.
Thanks.

[z34phoenix]

1st the cat wouldnt cause the cylinders to run lean.
2nd are all the plugs equally bad/lean? if so i would be looking for some kind of issue with the MAF sensor or air density thingy what ever those year cars had.
Next i would drop to a colder spark plug. nto sure the equivilent but the stock autolite plug for the lq1 is a #605. one heat range colder would be the 104 and 2 ranges would be 103. i personally run the ap103's (single platinums) but i have played with the spark and fueling in my tune. but i have found many DOHC's with white plugs... both from friends i have helped, my own car, and ones i have seen at the junk yard. i believe they commonly run on the lean side of things...

i would recomend runing atleast one heat range colder and runing 89 octane gas. also make sure the plugs are gapped at .045 they wont come gap at this and some of the old emisions stickers for the cars list .06 this is incorrect. .045 all the way.

i would also question the fuel injectors. i had an issue where one of my injectors was stuck open... so i was getting a lean SES and a rich SES at the same time! lol

[Obi-S. K.]

Thanks for your reply, Im buying a new car soon (06 GTO), so I havent really seen the urge to investigate, til yesterday

Replaced the plugs, and when reinstalling the wires, I noticed one of the plug wires was ripped. Couldnt believe I didnt notice this nor thought really crossed my mind since I recently replaced them.

Thanks again for the reply. Mods feel free to remove this topic