i got this lovely code in my 1500 5.3 and am wondering if anyone can help me out. the code means misfire in cylinder 5, so i did what most would do and swapped it for a new plug. i heard the ngk plugs are **** so i figured that was my problem. went with the ac delco .060 over the .040 i had on the ngks. changed all the plugs and again the same code popped up. i flip flopped the coil packs around from 3 to 5 and 5 to 3 to see if i got a different code again i got the same p0305. then i figured it has to be the plug wire, flipped flopped those from 3 to 5 and 5 to 3 and again the same code on the dash. im hoping someone can help me out with is. im thinking its the injector. at 1200 to 2000 rpm the motor vibrates hard and doesnt sound like its firing to keep the motor in balance. does anyone know what could be causing this? if it is the injector is it better to go with an ls1 or ls style motor injector over the truck injector? please let me know what you think. thanks

 

I would try swapping injectors like you were thinking.

As for what to get, that completely depends on what your plans are for the truck.

You could just buy any injector(s) and install them unless it's a stock replacement for your 99 5.3 motor. You'd have to tune for the change in bigger injector.

 

How many miles are on the motor? Could be bad/seized piston rings, I've had that happen before, drove me nuts until I comp. tested the motor, also could be an issue with the head,valves or head gasket, the intake gasket could be torn, swap injectors first to see if problem follows. Keep us posted

 

could be a broken valve spring. I've seen a couple with a broken spring in our shop.