Cylinder 8 misfire.

[Cassy]

I've a 99 Sierra 5.3 I got a diagnostic tool and I've got two codes that came up. The one is a cylinder 8 misfire. I replaced spark plugs wires and spark plugs, fuel pressure regulator. I think I did the coil check and the spark plugs check to see if I'm getting a spark. Anyone have any other ideas for me? I'm not familiar with vehicles and what I know is from you tube.

[riverbanks]

Free test,swap the coil with another,see if misfire follows

[Cassy]

Did that. Still read cylinder 8 misfire

[riverbanks]

Hmm,so intake manifold leak check,then swap injectors,a guy on here a ways back had a #7 problem,he decided to pull the rails,clean them along with injector intake, problem solved,?

[Cassy]

Was trying to avoid having to take off the rails and injectors. It takes me way longer than most to get stuff done. Took me 9 hours to do the water pump. I'll see if I can find any step by step you tube videos that show me how to take the rail and injectors apart. Would injector cleaner fix the problem?

[riverbanks]

I use techron alot,so if the spray pattern is bad on that injector, should help,if it's on the feed side,it's got no where to go, I'd try it,and you mentioned water pump,it didn't get hot,did it?

[Cassy]

I'm not sure if the water pump got hot. Heres my story, truck has always had the check engine light on since we bought it. It was a truck that was meant for hauling a few things to the dump. It was driven for several months when it sprung a fuel leak( oring on the cross over bar) it was still driven. Than the serpentine belt and water pump went which left it undrivable. Everyone kept saying they would come fix it and never did after a year and a few months I started watching you tube videos and decided I could do it my self. So I replaced the water pump and serpentine belt. Than I decided to get the diagnostic tool which lead me to replacing spark plugs, spark plug wires, fuel pressure regulator, the o-rings on the cross over bar. I cleared the codes and now cylinder 8 misfires, I checked to make sure spark plug had a spark, I switched the coil pack with another one. I'd rather continue to fix it myself as parks are expensive enough. I'm a girl with little knowledge on vehicles with a huge support team but I'm stuck and don't know where to go from here. The two codes I'm getting is the cylinder 8 misfire and EVAP solenoid. 

[riverbanks]

Ok,so try the techron cleaner,try a socket on intake manifold bolts, maybe a loose one on #8, another would be to spray a mist of water at #8 injector and manifold,listen for a stumble in the motor,might be a air leak, other than that, injector,big thing with that job is cleaniness,shop vac or compressed air to clean intake,so no debris enters injector holes,not a hard job with new orings

[chem_man]

Cassy, since you are serious about performing maintenance on your 99 Sierra, purchase a Haynes manual.  They are invaluable and well worth the money!!