I have a 96 OBS and a few days ago it started to throw a cel. I checked it out and it was cyl 4 misfire(P0304) and a egr flow(P0400). I replaced the plug and the P0304 went away for 2-3 days and now its back along with a small klunking noise, like something is loose inside the engine. I also know 2-3 of the vla's on the same side dont bleed up and make a tapping noise. I hope its not a spun bearking but any ideas on what the noise might be or how I might go about checking it out further. I also checked the compression and got 180 and 175psi on cyl 4.

any ideas anybody?

Could be the plug wire to that plug/cylinder. Could be an injector in that cylinder not spraying properly and cuasing missfires. I've had an injector go bad and not throw an ECU code OHMs resistance test on all injectors showed me the bad one.

 

Plugs and wires are cheaper; start there