96 misfire

[the4cbz]

96 GMC Sierra 1500 4.3. Just replaced cat/conv did full tune up and the msifire was gone. About a month later it started again. It comes and goes. Some times will run all day with no miss. I swear it seems like some type of vaccum issue. The CE Light blinks when missing. When hooked to computer only states that the number 4 cylinder has the misfire. If I rev up the rpm's you can hear a whistling coming from the defros vents when missing, when not missinfg no whistle. 125k miles

 

[Molson02536]

96 GMC Sierra 1500 4.3. Just replaced cat/conv did full tune up and the msifire was gone. About a month later it started again. It comes and goes. Some times will run all day with no miss. I swear it seems like some type of vaccum issue. The CE Light blinks when missing. When hooked to computer only states that the number 4 cylinder has the misfire. If I rev up the rpm's you can hear a whistling coming from the defros vents when missing, when not missinfg no whistle. 125k miles

Check all your vacuum lines and replace any that is damaged from dry rot. Good luck and keep us posted. Te other issue would be a injector going bad and will need to be replaced or cleaned.

 

[the4cbz]

I mistyped..160k miles...will try the suggestions soon..thx