lq4 2500hd p59 pcm throwing p0300 code, limp mode around 2k after relearning crank

[frchld92]

2004 gmc 2500hd lq4 6l p59 pcm 180k miles
the cats are gone and the exhaust is now 3 inch y pipe to summit 2 chamber muffler and 12 inch resonator.
everything else is factory.

i have replaced both upstream o2 sensors and disabled the downstream. i purchased mpvi2+ and aem wideband to tune for this and learn fuel injection tuning. my wideband is ran to pin 41 and 55 (blue) at the pcm to log it through egr. i figured out how to do conversions to maf err and ve err tables so it reads the math from the egr input. all checks are good there and i have fuel in the ball park of 14.5 afr.(and yes i know... lambda is better, but its confusing while learning everything else) the afr in the scanner matches perfect to the guage.

now to the problem. ive been chasing a miss as long as ive owned this truck and the p0300 code. the truck was bad lean with the new exhaust (i bought the truck with exhaust missing so idk how it ran before that) but after maf tuning it was running awesome except for a lean spot around 2k rpm. now ive switched to speed density tuning and am having a different issue at 2k rpm. it bogs bad, part throttle or wot. im not lean, it will eventualy start to knock but only 2-3 in most extreme instances where i lean on the throttle to induce it. the spark advance drops to negative values during this bog. ive also learned about crank sensor relearn and logging miss fires on the channels now. so 5 and 8 are getting up to 80 current misses during these bogs at 2k rpm or when giving throttle. now after i relearned the crank sensor the truck instantly goes to limp mode past 2k rpm with the same miss fires. i will swap 5&8 coils wires and plugs to #1&2 to see if it follows. wires and plugs are both new, i replaced them when i bought the truck.

il also note that i pulled the fuel rail and checked for leaky injectors and i had no odd plugs when i replaced them, ie wet or charred. and on my obd2 scanner before i bought the mpvi2 the ltft were -8 give or take and o2 voltage jumps erratically from .1-.9 going lean to rich constantly which is why i replaced the o2 sensors. no exhuast leaks btw.

the bog and limp mode happened after i relearned the crank btw while tuning for sd. i went back to my final maf tune where it was running great out of forced open loop. still the same issues so i believe it isnt related to my tuning or lack of. but possibly the crank sensor. i just want some advice before i start "changing parts" cringe....



i thnk that about covers it. i hope one of you is knowledgeable enough and or willing to chime in on this. im chasing my tail and cant seem to find my error.

[Shnraines]

Don't know about sd tuning, but your o2 sensors were working properly when swinging rich to lean as that is how they are supposed to work. Put it back to stock and see if the miss goes away and you'll know you induced it with tuning

[frchld92]

i actually tried this. i do every tweek to the tune 1 move at a time and save it and label it. ive tried the stock tune which is lean af and various other tunes and its throughout all of them. after digging deeper into crank relearn i believe i did the process wrong. it didnt go into limp mode until i did the relearn. hp doesnt give very good instructions. just rev it until fuel cutoff the cycle the ignition. and theres an ok button. the instructions i found digging are much more detailed and im sure i did it wrong. and thanks for the input on the o2 sensors. "sd tuning" was short for speed density, or tuning the volumetric efficency tables with the maf disabled. im very new to this but from my "diy" learning you force open loop and tune mass air flow to correct fueling for WOT, then disable maf for VE which is basically part throttle up to about 4000rpm. and i guess the tables blend together to always maintain ideal afr. but then again every time i think i got it figured out i realize i dont.

[Shnraines]

I know sd is speed density, just haven't done it. I don't understand modifying maf, as it is just measuring the air. Assuming it's properly calibrated, I would think the ve tables should be adjusted to fix fueling, not maf. Just watched pine hollow diagnostics video where fuel trims were way off on stock vehicle, and the injectors were restricted, or worn out as vehicle had 450k miles. Need to make sure basics are right before tuning. Should be able to get itself right stock or something is off. Fuel pressure, intake leak, bad injectors. Good luck