i have a stock lq4 (blackbear 87 tune) in a 03 2500. it seems to have a preignition/spark knock. under load , on the torque app on my phone, it will read around 4 degrees of knock retard. i can hear it and its been happening for a while now. i changed my fuel the last tank to mid grade and still can hear it. next fill up will be 93. i have changed knock sensors and intake gaskets.

also the engine runs well minus the spark knock, besides at idle when its warmed up (open loop i think ) it idles rough and missfires. i can confirm the missfires from the scanner. checked the o2 sensors and they move voltages as normal. it has new plugs/wires/cleaned maf/ fuel filter. im dumbfounded and hope yall could shed light upon this crap!

 

Any performance tune worth paying for will require 91 or better fuel

 

i agree but regardless of the tune it was still knocking on my stock pcm

 

i have NGK Iridium plugs gapped that were pregapped to .40 also

 

no one has any insight?

 

I have a similar issue. Just replaced my delco iridiums that were blow the heck out originally gapped at .060 and I was having the random misfire code. Replaced them with Tr5's gapped to .040 and it runs wayyyy better but still picks up 2,4,6,8 misfires at idle and under 1700 rpm. Above 1700 rpm its fine no misfires or detonation. The only thing I can think of in your situation is get a re tune or flash back to stock and see if the knock is still there. Timing may be too high in the tune. Either that or the knock sensors are reading a false knock

 

I use the torque app to monitor as well

 

for the missfire i dont think it would be a vacuum leak or anything mechanical like that. im pretty sure it has to be somthing electrical because it idles fine when the pcm is in a open loop but when its in a closed loop it goes to ****. i read my o2 sensor voltages and the do go from a high to a low number every few seconds but not excatly .01 back up to .08 then back to .01 again and etc... its more like .07-.04-.06-.01 both of the front 02s seem to kind of have erratic readings

 

changed 02's nothing changed. checked the pcv and its hollow. complete straight through? i know this isnt right?

 

If your truck came equipped with the "fixed orifice" pcv valve then that is perfectly normal. The "fixed orifice" valve was an update to the older rattle valve style. The updated piece was supposed to fix oil consumption issues. I would certainly say look into the tune/electrical side for your problem.