05 c15 accert mxs motor issue need some help

hello all, new to the site been learning a bit already, but i have a issue with my 05 peterbilt with a c15 accert set at 475, the seriel number says its a mxs engine, i took it to peterbilt for the 2nd time in 3 months for a check engine light, intake valve accuator, 1st time harness end was off or something like that, got it back still ran like a tird no engine light though, took it back yesterday for the cel again, same code and the accuator was a different cylinder, same result wire connection,while there i asked them to look why the front of the motors exhaust manifold is chalky red and the back is normal, did nothing the first 2 times i asked about it now they checked it, said the #2 cylinder is overfuelling, tempertures are 400 degree hotter than the other cylinders, so the replaced the injector in number 2, well still same issue, they say the have no idea call tomorrow,id imagine im paying for a injector and labor for nothing which is not too good but still have this issue, anyone have any input on this? should i pay for the injector they misdiagnosed? any one had this issue before? sorry for the novel just want to explain as much as i know about it any help will be greatly appreciated