Random misfire primarily in cyl 6

[chance olson]

Hello Everyone

I'm working on a 97 GMC suburban with a 5.7l vortec. it has a P0300 random misfire code that i cannot figure out and is primarily in cylinder #6

what I've done

-Compression is roughly 160

-replaced spark plugs/ wires

-replaced cap and rotor

-replace spider injector with upgraded unit from ac delco

-replaced fuel filter

-pulled distributor to check gear, nothing wrong and check position with scanner afterwards

-pulled valve cover, push rods and valves all move (not measured, but nothing appears broke)

-spraying an brake clean into the intake causes the engine to run smooth and stop misfiring/ misfire goes away at 3000rpms (watching reading on scan tool for misfires)

 

At this point I'm thinking a hydraulic lifter, or an issue between the spider injector and computer or computer it self

Edited October 11, 2020 by chance olson

[riverbanks]

Should you hand spin motor over,and watch hight of rockers?thinking worn cam lobe?or really look close for a cracked valve spring?or was the spider shot for a while?,carbon on intake valve on 6?