Thread: Negative LTFT, Knock Retard advice.

Hello everyone I had a couple issues with my l67 upon fixing them other things are popping up and I'm looking for experienced advice.
So car is a 98 GT Coupe(stock L36) that i top swapped.
Exhaust (Manifolds crossover and DP) is all stock except u-bend delete.
Ported gen 3 M90, and ported LIM, running stock 3.8 pulley. CAI, 180* thermostat, autolite 103's, and ZZP 1.0 PCM tuned for 91 octane but running 93. Approximately 3k miles on top swap.

It started a couple days ago. Car ran exceptional decide I'm gonna go to the track for some fun. Figure it would be best to scan and make sure everything is in order. Everything looked good no knock, car pulls hard then i notice my LTFT lingering around +16%. Grabbed some carb cleaner thinking i had a vacuum leak, found 3. a leaking hose on SC tree, leak at PCV and EGR. sealed them all up no more leaks. However now my LTFT are inbetween -16% to -26% at idle, cruise, or decelleration.
During acceleration under load the fuel trims even out to acceptable numbers but as soon as i let off throttle they go back to high negatives. Peaking around through torque scan i noticed during idle if i blip the throttle a little bit I'm getting random misfires upon revs dropping to normal. According to torque scan all my cylinders occasionally misfire with #'s 4 and 5 being the worse. Pulled all the plugs and they all look the same a bit white probably from running lean with leaks for however long but not bad.
Reinstalled plugs. decided to throw in another FPR i knew was good i had laying around because i smelled faint gas in the vacuum hose. Unplugged battery for a few hours to reset fuel trims and took her for a spin. Feels good but LTFT are still chilling around -20% and i noticed 2 degrees of knock during a 2-3 shift at WOT. So i park to check things out. I'm still getting occasional current misfires in all cylinders but 0 under history not enough to trigger CEL apparently. But i can feel the surge and shake from the mis at idle. I snapped the throttle under frustration to hear that sweet SC whine and i noticed my scangauge read 7.3 degrees KR. Another thing i just noticed is slight gas smell in oil i will do a change asap.
So to reiterate car ran good with vacuum leaks aside from high + LTFT. no knock under any condition. Not sure about the misfires though. After fixing vacuum leaks it would appear im running too rich and its causing me to knock like a mo fo.
MAF, MAP, TPS, IAC, and ECT sensors are relatively new and showing correct values. O2 sensor was replaced 10k ago and I'm not sure of normal operating specs for that.
I do hear an occasion tick or click from DP/CAT area at idle. Anyone have experience with ZZP PCMs? Do they tune them on the richer side causing my LTFT to be high negatives? Do all engines have occasional misfires? Is it something i shouldn't worry about until it triggers a CEL?
also i thought KR was more prone to happen when running lean. How come i had no knock with vacuum leaks causing lean condition. But after fixing leaks and now running rich i have knock?
Any ideas? I don't know where to go from here besides making vacuum leaks to even out trims.

Also does anyone know if an exhaust leak before upstream O2 would cause a lean condition (high ltft) or a rich condition (low ltft)? this may be my problem though the leak would be small because it's not that loud.

Any advice or info is appreciated. Educate me!

which so cold of a range of plug? you don't have enough mods for that cold of a plug.

I don't know off hand what they read at WOT i know at idle the upstream was reading .16v and the downstream was .18v I'll get the WOT numbers tomorrow. I have like 20 of the l67 injectors all got from junkers most likely one or more is not right. Hopefully i have some good ones in my pile.

Alright time for an update.
I switched out 5 of 6 injectors changed oil and removed battery for a few hours to reset trims.
LTFT seems to be slightly better it peaked at -19% instead of -26% but only at idle or decelerating. Cruising or accelerating trims are perfect +/-5%.
Didn't register any knock, even on some spirited runs up through 2nd.
O2 sensor #1 reads .96v at WOT sensor #2 reads .95v at WOT.
Still have some misfires at idle but instead of every cylinder being affected its only #3 and #5 now. Maybe it is the injectors and it just so happens most of mine are bad.

I'll switch the plugs aswell just to rule that out as possible cause of the misfires and running rich.

Thanks everyone for the advice and help.
After scanning the past couple of days I've found that i have no knock and no misfires but LTFT still slowly climbs to -19% at idle. We'll see what happens when i install headers but my money is on the injectors. Guess i need to throw more mods at it so i have an excuse to get some 42# injectors.