Hi Guys.
I have a 2000 chevy suburban 5.3L V8. 192 k miles. The missfire is on cylinder 4. I was reading a bunch of threads for repair and diagnose but still cant fix my problem. I hope find someone with similar experience who fixed his own problem.

The missfire was intermittent and came on daily driving. I tried to diagnose and fixing but it sooner or later always come back. I was changeing the spark plugs ,coils, new intake seal, new crank sensor, new konck sensors.

Replaced the catalytic converter and o2 sensors. The missfire was never showing when the engine is cold. in cold starts, in the morning the car runs fine for 15-20 minutes. after 20 minutes starting the missfire and shows the P0304 code.

sometime the missfire disappear after 3-5 minutes but most of the time it missfiring until I stop the car. Compression test was 135 on 4 on light warm engine, but I could not test when misfiring because the engine is to hot.

Swaped injectors new coils and plugs but the missfire stays on cylinder 4. I was reading threads about weak valve spring failures but it suppouse to missfiring all times with bad springs or not ? I want to solve this problem but dont
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wanna change everithing what is not necessary. What is can causing the problem just after 20 minutes with the warm engine and not showing in cold starts? Thanks any advices and ideas.

when the engine runs Right Not make any noise . runs like it shoud.