Misfire
TECH Senior Member
Joined: Jun 2016
Posts: 22,288
Likes: 3,615
From: Central Cal.
A broken spring would drop the valve a bit, but maybe not enough to hit the piston. Compression would be closer to zero if a valve was open a bit.
Look up the codes to see what they mean.
Look up the codes to see what they mean.
Put a bit of oil in cyl 4 and see if the compression comes up a bit. If it does, you are looking at piston ring failure. Your next step should be a leakdown test.
PO300 is multiple misfire
PO304 is cyl 4 misfire
PO300 is multiple misfire
PO304 is cyl 4 misfire