Problems on my Cummins ISX

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Hello everyone, I'm new here on forum and I need your help.
I have a Cummins ISX that knock at 1450 -1500 rpm. At the last service, they have completely overhauled the engine, replaced one injector, replaced the camshaft on the valve train, clearance checked the timing gears (all within specs), new head. Still have the same exact noise as before and the men from service said they found no damage in pistons, pins, cannot figure it out.

Somebody told me to use a dish tool to cut out injectors,and if i need to isolate the cylinder that has the knock, it sounds like an injector causing the issue once I can isolate swap the suspected cut injector with another cylinder, all injectors should be changed at time of overhauls. Or I'll risk damage to the overhauls engine. I know that an injector only has a life span of 500,000 miles.

Do you think is too difficult? What you recomend me, to buy the service manual for my truck (TradeBit.Com) and to save money by repairing it myself, or you recommend me to go on a proffesional service and to solve this problem.

Thank you for your attention!
 
I would personally recommend taking it to a specialized fuel injection shop. If it is an injector, other than swap it there is little else you can do on your own. Pop off pressures, spray pattern, and the electronic magnet end of the injector could be an issue.

On the other hand, could be as simple as needing a strong dose of injector cleaner. If you have ruled it out, chances are you will need atleast to buzz test the injectors, which only a computer will do.
 
Did you take it to an official Cummins OEM shop? Dealers and third party shops are not always the best way to go in isolating a motor issue. How many miles on the ISX?

A Cummins ISX injector only has life span of 500,000 miles? What lame brain told you that line? I took a Cummins N-14 to 1.4 million and it only got one injector in that time, and the motor was never opened up for a repair. My last ISX, I sold it at 968,000 miles and it still had all original injectors and no rebuild or inframe. Both of these trucks went right to work for the next owner. Second one passed me one day on I-74 going to Indianapolis a couple of months after selling it.

I would have a Cummins shop do an injector cleaning procedure on the injectors. They have a specialized cleaner that they manually run thru the injectors, rails, etc. Not some fuel additive kind of thing. Also, check to see if the primary fuel pump is up to par, not the lift pump. They are notorious for developing leaks that would affect pressure.
 
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