just had mine fixed at the shop. they were able to find injector #1 to be plugged. i was not able to determine that with my computer. odd though, that it did not throw a #1 cylinder misfire, but rather a 'random/multiple' misfire. that certainly made things tough for me to figure out lol

 

im still tring to figure this one out.... so new parts are as follows : fuel pump, fuel filter, plugs, wires, front o2 sensor, passenger side manifold(it was cracked when i bought the truck) pcv, and cpu. It keeps misfiring on number 7 and 8 cylinders. Its got lots of compression, the coils are good (switched them around), injectors are firing. The grage checked the intake dome for leaks nothing, checked grounds, switched number 7 injector with 3 and still misfires in 7 and 8. After this they told me computer so i got one online, programmed and then put it in and it did nothing. so then I took out the back o2 sensor and took it for a run to see if it made any difference, but no luck... but i didn't get any codes from removing these o2 sensor. then when i put them back i now have loose pieces in my cat... would plugged Cats cause this? So im getting a new cat put in on Wednesday but i still don't know if this is going to fix my problem. I was also told to change the back o2 sensors to fix this problem.

 

Hey Itibiti...did you ever figure out the problem?
I am exactly where you were at on my 2007 5.3l.
I have a mechanic friend who said could be a pitted cam lobe.

 

I'm having the same issue. Started out at cylander 7 misfire now it won't hardly move saying multiple cylander misfire. I've changed fuel pump, filter, crank sensor, plugs wires, fuel pressure regulator. I've also been told a lobe off the cam idk im.lost with this one any help appreciated

 

I went ahead and removed the heads. Turned out to be carbon build up at the valve edges. Found a guy that deals with these frequently and he recommended. He talked me into buying non-AFM conversion and as soon as I took heads off, he showed me the buildup. Never had a problem since.
Do you have a scan tool to measure how many misfires per cylinder?
If you do, count how many misfires per minute on each cylinder. I had a few hundred misfires on two cylinders.
You can then try Seafoam which should cut the misfires in half or bring the misfires under the threshold where the computer thinks its normal and get rid of the CEL. A guy recommended that to me which made sense but I never got to try.

 

all my problems were injectors.... had to replace all of them.

 

Has any ones had the misfire code and check fuel pressure? I have a 2016 suburban 5.3L that started with Evap codes then fuel pressure. Changed evap and changed fuel pump. Sluggish at times going up hills. Fuel pressure hunts rapidly from mid 30s to upper 50s. Can not figure out what’s going on.