Cummins ISX Fuel Pump Failure symptoms on 2012 Kenworth T-800

Good day to everyone
Hope I posted on the right forum.

Hopefully somebody would be able to relate to this problem and offer me some guidance before making a mistake. Ill try to explain and provide as much info as I can. Please feel free to ask questions.

I have 2012 Kenworth with a Cummins ISX 15 450. (Engine No 79554126). I’ve been having issue with power delivery. Truck seems to be doing fine when suddenly you feel the loss of power, if you take the foot out of the gas pedal kinds of breath and gets back to normal. However, even when it is idling the issue shows up. (I am not sure if this started before or after I noticed the issue)

Apparently, the issue is high pressure fuel / on the lines. When idling, the fuel pressure gauge goes all the way up and you feel the engine running rough. I replaced the fuel pump about 2 years ago, bought directly at Cummins. Fuel pump 2872399.

Summary, when idling (not touching it at all) fuel pressure claim all the way up, truck runs bad, fuel pressure goes down, truck runs fine again.

What the mechanic have tried:
1) We changed the regulator on the back of the pump.
2) Fuel lines seem to be fine, return fine.
3) Bypass fuel filter and connected directly to fuel tank.
4) We tried another fuel pump (we don’t know if it was a good pump, but same symptoms if not worse)
5) Disassembly head of fuel pump and rollers seem to be just fine among other things.

What should I try? send pump to test it? start replacing...?

 

Sorry guys for not responding. Ive been OTR.

We finally solved it. Apparently there were debrits, more like rubber waste on the fuel line after the main filter and the pump.

Perhaps a fuel paper filter base came lose and caught in the line.

Truck has been runnig well past few days. Thanks for help and ideas.