What Could It Be?

[Mudddawg]

Hey All,

My brother has 98 Z71 with the 5.7. Getting a cylinder 4 misfire code(cant remember the #). We have replaced the fuel pump, FPR, plugs wires distributor cap rotary button intake gasket and had compression and injectors checked. Still have the same problem. We can reset the code and it comes back right away. However, if we remove the tube that connects to the passenger valve cover and and intake tube the truck will run for about 2 hrs before the light comes back on. We have heard of other trucks of the same setup in our area doing this, but never heard exactly what causes it. Some local mechanics say sticking valves, some say burnt valve. The truck has about 230,000 miles on the clock and still runs strong. It does have a miss that can be felt but you cant feel it above 1800rpms. Any advice? Thanks.

[GMstrong]

EGR valve,or intake gaskets.