How can I tell if my truck has a burnt valve?

[marcusw_79]

I bought a 96 ford ranger a few months ago, but it was miss firing real bad. I took it to a few shops and they said it needed a tune up. I changed the wires,plugs,fuel filter,oil,coil packs and air filter and its still doing it. I had it put on a computer not long ago and it said cylinder 4 is miss firing. It only does it for a while until it warms up.

 

[LeslieR]

Compression test. Did it have a blown exhaust gasket before the tune up? This is the #1 cause of a burnt valve.