hi,, i am new ...i have owned a number of tahoes, and yukons..97-99, love them..i bought a 99 yukon, at a good price (now i know why) i have a misfire code, #3 code is p0303 i change the injector, and plug,,wire is good...my mechanic says it is a valve,, hanging up... compresion seems good... the truck, sputters... cranks a few times...then starts..ruff idle... if you go for a ride,, it sputters, but gets going.. there is power still there,, has anyone had this problem??? and is there truth to my mechanic?? .. i like my mechanic...but when you spend 1000 on your wifes jeep...for a front differencial...and it is still making the same noise..and your mechanic says...ooohhhh its the transfer case...you want to second question him....if anyone can help,, i would really apreciate it...need to be in this truck for short money...or need to get ride of it...extra truck,..wife don`t like that...
thanks,,Manny

 

Do you feel ok doing work yourself? If so, or not, try some new spark plugs. You may need new plug wires and maybe a cap and rotor. Your mis fire should be in the ignition system, not the valves.