So I have a 08 suburban ltz that I am stuck scratching my head about, it has a p0300 misfire and is running pretty rough and I just cannot figure this out, everything I have replaced so far- camshaft and lifters, Vlom, one injector because it started out as a cylinder 3 misfire, all plugs wires and coils I’ve cleaned all injectors and replaced o-rings, checked for vacuum leaks, checked for pulse on injectors and made sure spark was good, O2 sensors are working normal, maf is clean, throttle body is clean too, It is running very rich and I fear cat damage if I keep starting it as it’s starting to stink pretty bad now, haven’t drove it since I replaced the lifters and cam because it didn’t help, thanks for any advice, I have some pictures of all the data off my scanner if that would help anyone to decipher this thing

 

Did you visually verify there is good spark ?
monitor fuel trims? An injector balance test wouldn't hurt.

 

yes spark is 100% good another thing I should mention is when the fuel system is in open loop there’s always a fault on both banks.

 

have you tried a compression test? How many miles on the engine?

 

i have not done a compression test yet because I don’t have the right adapter and when I had it in the shop originally the mechanic refused to do a compression test because he swore up and down that it was a camshaft issue and the test wouldn’t show anything but in his defense one cam lobe was pretty shaved.and 124xxx

 

sounds like the engine was near catastrophic failure. Could have a stretched chain or other deeper issues requiring rebuild.