Chevrolet Repair: engine miss, gmc 1500, leakdown test

Question
i have a 98 GMC 1500 4x4 with a 5.7 vortec. I'm experiencing an engine miss on cly. #4 I have replced the spark plugs and wires,the cap and rotor,and the fuel injector poppet valve.The #4 plug showed signs of oil burning. The center tab on the rotor was broken and had started to burn a hole in it and the cap was real corroded inside.I thought that would've had fixed it but it didn't. I ck the commpression on all the cyls., they were all 115-125 lbs. I removed the valve cover and cranked the motor over the valves seemed to be opening all the way. I then replaced the fuel injector poppet valve thinking that might be the problem since i had no way to test it but no good. I've done all i can think of just wondering if you might have any other ideas. Thank you very much.

Answer
Heya,

 You should probably finish your diag with a leakdown test but what I can tell you is that those engines have problems with the fuel injector plastic lines melting, cracking and seeping. If you have the equipment do a balance test and don't be surprised if the injector line that's is leaking is not the cylinder that is missing. I know what you are thinking but when you pull the top half of the intake and pressurize the lines you will se what I am talking about.

W