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ISX 12 code 4726 and 0559 - FarmLife - 02-06-2025
I have a 2015 Peterbilt 365 with a Cummins ISX 12 CM2350 engine serial number 75035614. The truck has trouble starting and is smoking black. The rail pressure is bleeding off as soon as the engine stops cranking. I have capped off all the injectors at the fuel rail and it still loses pressure as soon as you stop cranking. I also noticed the lift pump is not working. If you supply the lift pump with 12 volts it works. There is only3.5 volts coming from the ecm. I tested the voltage at the pump connector and at the ecm. Both show 3.5 volts.
My next thought is to try running the engine with 12 volts supplied to the lift pump and see if that clears things up with the rail pressure. If it helps with the rail pressure I am thinking about swapping an ecm from another truck.
Any input would be appreciated.
RE: ISX 12 code 4726 and 0559 - Manjot12dosanjh - 02-06-2025
I would also check the pressure relief valve on the rail aswell
RE: ISX 12 code 4726 and 0559 - FarmLife - 02-06-2025
I took the banjo bolt off the fuel pressure relief valve, and no fuel came out
RE: ISX 12 code 4726 and 0559 - marek4792 - 02-06-2025
Injector tubes
Relief valve
Fuel pump plungers sticking and/or failed.
Tired Injector(s)
RE: ISX 12 code 4726 and 0559 - FarmLife - 02-06-2025
I swapped a fuel rail relief valve with another truck. No change. Ran another fuel system leakage test. It will build pressure to 21,000psi. The commanded pressure gets up to 29,000psi but the measured will only build to 21,000psi. It still leaks all the pressure off as soon as you turn the engine off. I swapped an ecm from another truck and now the lift pump is working.
I think I am going to remove the high pressure pump head next.
RE: ISX 12 code 4726 and 0559 - FarmLife - 02-06-2025
Removed the high pressure fuel pump head. Put shop air to the port on the front of the pump to extend the plungers. The plungers would not move. Was able to take off the springs and pull the plungers up by hand. When you push the plungers down they come back up like they should. Since the plungers would not extend with shop air does this mean the check valves in the top of the head are stuck?
RE: ISX 12 code 4726 and 0559 - Rawze - 02-07-2025
(02-06-2025 )FarmLife Wrote: Removed the high pressure fuel pump head. Put shop air to the port on the front of the pump to extend the plungers. The plungers would not move. Was able to take off the springs and pull the plungers up by hand. When you push the plungers down they come back up like they should. Since the plungers would not extend with shop air does this mean the check valves in the top of the head are stuck?
there is more to testing the plungers than just pushing on htem... here is the way to test them...
ref: http://rawze.com/forums/showthread.php?tid=6778&pid=60008#pid60008
if the ecm has delete programming in it...
A)> make a copy and send it to me for a review. Fo all anyone knows, some yahoo could have jacked with the fuel pressures, cauysing damage to the fuel system of pump over time... damage ti the engine, turbo.. who knows.
info: http://rawze.com/forums/showthread.php?tid=8425&pid=72945#pid72945
b)> after making a successful back copy of the programming (using Calterm), put latest factory programming in it and see if it has the same issues.
RE: ISX 12 code 4726 and 0559 - Rawze - 02-07-2025
as far as capping injectors and doing leak-down ... , do up to 3 at a time.
RE: ISX 12 code 4726 and 0559 - FarmLife - 02-07-2025
Thank you for the response Rawze. I sent this demandate file to you before I ran it. I have a new ecm coming with the factory programming. Going to run it and see if anything clears up and then demandate that ecm. I am also putting a new fuel pump head on.