Need help with engine issue
Hi everyone, I have a 2018 GM 6.2 L86 truck with a no-start issue after replacing the lifters, cam, timing kit, and head gasket for a minor lifter tick. Before the repair it ran fine aside from the tick, but now it cranks with a very low-compression whirring sound and won’t start. Compression test shows 5 psi on all 8 cylinders. During diagnosis, removing the intake rocker on cylinder 1 made compression jump to 150 psi, and I repeated the same result on multiple cylinders across both AFM and non-AFM banks: removing the intake rocker and forcing the intake valve shut restores compression, reinstalling it drops compression again. The exhaust side does not behave this way. I rechecked timing marks with the timing cover off and timing is correct. There’s no metal in the oil/filter, pistons and cylinder walls look good on the scope, and adjusting pushrod length with an adjustable pushrod didn’t help. It seems like all intake valves are being held slightly open at the wrong time, but I can’t figure out why. Any ideas on what to check next? Thanks!