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Hammerhead

The injectors in the photo were all fresh 4088665PX reman injectors. Number 2 & 6 had failed the bubble test and were replaced on Thursday. After a good warm up and test drive, the fuel knock sound was not gone. I reached out to a member from Vegas and he told me to come by his shop on Monday. We went for a test ride to demonstrate my issue, and he graciously offered me his shop to continue work and tests.
We bubble tested again, and this time had multiple injectors failing with bubbles while cranking, but could not get conclusive results barring the motor.
I installed a set of smaller injectors he had at his shop, and we retested, both bubble and drive. We were suspicious of a cracked head, into the fuel galleys that was giving us the random bubble test results. This was when my host called Unilevers to get his thoughts. Uni says the odds of cracks like that are 1/1000, that's about my luck!
Same result with the bubble tests and fuel knock sound while driving with my hosts injectors in my truck.
I made the decision that regardless, cracked head or not, I now have two fresh injectors with 4 that have nearly 19000hrs on them...of above average workload. This was when I called Uni, cause I was still betting on head. I was going to replace the other 4, due to both, hours, and the potential damage the leaky ones or cracked head had done to the other four.
So three trips to KW yesterday for the four remaining ones, heads up QC may be an issue check your injectors closely, I put the four fresh ones in with the two in the pic (2&6) that only had ~6hrs or so on them in, installed the rocker arms, barred the motor to "Insert Pin" to double check cam timing (good), then barred to A...and I was told to put down the tools, supper is ready!
I washed up and was handed a beer and BBQ was just hitting the table! I took the rest of the evening off to contemplate my situation.
Fresh start this am, ran the overhead adjustment, put new fuel filters on with some oil added to them to ease the new injectors in, and settled in to install a new alternator belt on my APU because mine broke while I cycle the lift pump a few times.
Fired up the APU, and now I know why the belt broke, my APU alternator was seized! Are you starting to see why I'm betting on the 1000:1? Turned the master off for it, and cranked up the ISX with new injectors. Let it pop & fart for a while to completely purge all the air out of the system, then I pulled it outside to let her warm up for the test drive. It ran so nice n smooth!
40 mins or so later, at operating temp off we go. Apply brakes and throttle to create torque load through the rpm range, and all sounds good. I swear I can still hear something, but my host says no, it sounds great and you're looking to hard. He thinks I'm mistaking gear lash and compressor noise with my fear and hypersensitivity.
So long story short, one or more of those other four injectors was bad, but wouldn't conclusively show itself with the bubble test. The truck runs considerably smoother than before.
It's a concept called "Deviation of Normalcy". Basically it means that something slowly degrades over time and you don't realize how bad it has gotten until you fix it. That was the condition my injectors had gotten to...unless, I am in Vegas after all, your looking at my cards...1000:1? I hope not.