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DR.Cummins
DR.Cummins, FIELD SERVICE TECHNICIAN
Category: Heavy Equipment
Satisfied Customers: 3084
Experience:  16 Years working on Cummins Diesel engines,
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Hello we have an ISX cummins and it starts and runs fine but

Customer Question

Hello we have an ISX cummins and it starts and runs fine but when a person drives it and it the rpms reach 1500 or so and runs good for about 15 seconds then it surges also we put a clear line on the return line to the tank and it has lots of air in the system when the motor runs. When the primer pump runs it brings the air out of the system then it is solid fuel. But only when the engine runs it brings air to the return line. We have gotten the injectors rebuilt and checked the fuel line to see if there is a crack in the line but there is none we have also replaced the mechanical lift pump. We had also had some oil in the fuel but we think that the problem was there because the mechanical lift pump had a seal leak. What would cause that hesitation or surge at the upper rpm? and also why would there be air in the line?
Submitted: 3 years ago.
Category: Heavy Equipment
Expert:  DR.Cummins replied 3 years ago.

Hi are they any check engine lights on? What is the engine serial number
Customer: replied 3 years ago.
we had an engine code at first which read " low feul pressure but is acceptable" that was before we install the upper mechanical lift pump but right now there is no engine light.

Engine serial number: 79208911
Expert:  DR.Cummins replied 3 years ago.

ok first off no low fuel pressure code is acceptable the code was most likely 482

The fuel pressure is monitored by the ECM. If the rail fuel pressure is lower than an acceptable level for a given set of engine operating conditions, the fault code is logged.

NOTE: One possible cause of this fault code is a damaged or sticking drain-back valve located in the fuel supply circuit in the integrated fuel system module (IFSM). The IFSM is located directly above the fuel lift pump. You have an electronic lift pump not mech. This means you replaced the main fuel pump on the top of the isfm? and the electronic lift pump that runs for 2 min at key on is not changed? (verify operation, key on and listen ).You need to start from the beginning You should hook up a clear line on the supply side to the engine see if you have air there going into the engine. If needed bypass the tank lines ect by running the engine off a 5 gal bucket of fuel to duplicate the problem,

Expert:  DR.Cummins replied 3 years ago.
By the way oil in the fuel has no connection to the lift pump or pump. That is caused by Cylinder head is cracked,or damaged injector bore, Injector o-rings are damaged,

Integrated Fuel System Module (IFSM) mounting gasket leaking, These are also causes of excessive air in the return line. The head should be pressure tested

DR.Cummins, FIELD SERVICE TECHNICIAN
Category: Heavy Equipment
Satisfied Customers: 3084
Experience: 16 Years working on Cummins Diesel engines,
DR.Cummins and 4 other Heavy Equipment Specialists are ready to help you
Customer: replied 3 years ago.
We have two pumps the lower pump is electrical under the IFSM and the upper is mechanical which supplys fuel to the head that one has been replaced. We replaced it because the inner shaft was worn on the seals. We think the oil getting into the fuel is because the shaft was worn out and the seal failed to seal the oil from the fuel side of the pump.
Expert:  DR.Cummins replied 3 years ago.
That will not happen the only way to get oil in the fuel is the way i described. Is the lift pump working?
Expert:  DR.Cummins replied 3 years ago.
any luck
Customer: replied 3 years ago.
Hey sorry about the delay we were busy yesterday with other trucks we have not had a lot of time to look at the truck that you are helping us with but we hope today we will have more time to take a look at the information you have givin us. We'll try and get back to you as soon as possible. Thank you for your patience.
Expert:  DR.Cummins replied 3 years ago.
Ok
Customer: replied 3 years ago.
Hey we have worked on it alittle more we have nerrowed it down to the IFSM and you were talking about a drain back valve. "One possible cause of this fault code is a damaged or sticking drain-back valve located in the fuel supply circuit in the integrated fuel system module" Do we have to remove the whole IFSM for taking that drain back valve out?
thanks.
Expert:  DR.Cummins replied 3 years ago.
The drain back valve is located above the lift pump. In the isfm, remove the lift pump to acess the valve
Customer: replied 3 years ago.
Hey we have worked on it alittle more we have nerrowed it down to the IFSM and you were talking about a drain back valve. "One possible cause of this fault code is a damaged or sticking drain-back valve located in the fuel supply circuit in the integrated fuel system module" Do we have to remove the whole IFSM for taking that drain back valve out?
thanks.
Expert:  DR.Cummins replied 3 years ago.
No it'ss above lift pump,remove lift pump and it is up there

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