97' sierra K1500. 5.7, cylinder #4 wont fire..

[jeradciesielski]

My truck's check engine light came on so i had a local mechanic shot diagnose it. They told be Cylinder #4 was missing a lot and something about that being just at idle rpms. And cylinder #3 was missing a tad to. Anyone have any idea what it could be? valve maybe? idk.. And i already checked basic stuff like plug and wires.. HELP!

[gmtech4]

cap,rotor,???

 

swap plugs around and injectors ,,,,,,

 

ya need a scanner to follow the miss ,,,,,

 

or take it back and let them do it

[jeradciesielski]

Thank you, and ive come to the conclusion the light goes off when im driving down the road eventually. but when it just idles it comes on and starts blinking, and i notice the miss.. Any think else you can think of?

[1997SierraSLT]

sounds like the classic P0300 "random misfire". These first generation Vortec engines were notorious for misfires due to the poor poppet valve design. GM issued a TSB years later and revamped the fuel injection system to eliminate the poppet valves. Here is an example article. If you type in CSFI to MFPI in Google, there is a wealth of articles, etc.

 

http://www.fuelinjector.citymaker.com/Vortec_spider_fuel_injection_conversion.html