Cummins ISX15 Fuel Pressure Issues

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by OutlawW900, Dec 2, 2021.

  1. OutlawW900

    OutlawW900 Bobtail Member

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    Hello, I own a 2014 KW W900 with a 2013 ISX15. Bought it two months ago and have only worked it two weeks. After the first week it started showing SPN 157 and SPN 95. First code is low fuel rail pressure and second is clogged fuel filters. Both codes turn on the check engine light with the wrench in the middle. The truck also looses power when either code comes on. These codes come on weather I’m bobtail or loaded. Any time the truck has to exert a bit of work they come on. The truck also shuts off sometimes pulling hills and lately it’s shutting off at idle sometimes. When it shuts off it has SPN 157 which is the low rail pressure code. I’ve changed fuel rail pressure sensor, ECM with new programming, high pressure fuel pump, had my tanks opened and cleaned, had my tanks pressurized to see if fuel would blow out the lines, have changed fuel filters many times(sometimes with the codes on and they stay on), had the fuel filter housing checked. The only thing left to change is the fuel lines(which were also blown with air in case of debris clogging them up), primer pump, ECM/engine wire harness and fuel rail check valve (which I haven’t done because if this valve was bad it would struggle to start and or misfire. Also the whole SPN 95 with new filters is confusing. I’m writing out of desperation because none of the shops I’ve gone to have been able to solve this and I’m up to $12k in expenses on this. If any one has any suggestions or ideas, please I’m all ears.
     
    biopure22 Thanks this.
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  3. Alan M

    Alan M Bobtail Member

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    Dec 3, 2021
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    A bad injector can cause those problems. I've had just one injector cause the engine not to run at all
     
  4. Goodysnap

    Goodysnap Road Train Member

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    You need to get to a shop that knows the engine or to troubleshoot the fuel system properly or guessing until the cows come home will get expensive. Could be air, could be injector, could be relief valve. Lots of possibilities.
    If you know the engine and know the fuel system the diag is quite simple but necessary to replace the correct components to correct the fault.
     
    Oxbow Thanks this.
  5. OutlawW900

    OutlawW900 Bobtail Member

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    Thanks guys. Today we replaced the fuel rail check valve and another check valve that goes behind the block towards the firewall. We also tried running a direct fuel line from the primer pump to the left fuel tank. Nothing seems to work. As far as the injectors go, I’ve had an injector performance test(with Cummins insight) done twice. They all passed. We’ll see what happens tomorrow.
     
    Oxbow and Goodysnap Thank this.
  6. Goodysnap

    Goodysnap Road Train Member

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    The injector performance test can pass and still log faults. Check fuel rail decay. Run fuel system leakage test and record pressure lost per QSOL. If fail. high pressure Pump and relief valve are new and unlikely the cause. Measure injector leakback to isolate defective injectors.
     
    Oxbow Thanks this.
  7. OutlawW900

    OutlawW900 Bobtail Member

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    Ok will ask them on Monday to run this test. Today we were monitoring the commanded pressure vs the actual pressure and noticed that they were almost identical until we got up high on the rpms, there was a difference of almost a thousand psi short. Also the truck showed the SPN code 157 active even when truck was off. So on Monday we’ll also check the wiring harness. There’s still a consensus amongst some of the shop guys that it might be electrical. I don’t believe so but we’re running out of mechanical things to do.
     
  8. Goodysnap

    Goodysnap Road Train Member

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    The high side pressure won’t fall short enough to log the fault until you reallly put the fuel demand to her with a load, when fuel demand is the highest.

    The decay test proves that the high side fuel system has a leak. It should hold steady and not bleed off. It may fluctuate 2 or 300 psi, but will not drop over time when it’s tight.
     
  9. OutlawW900

    OutlawW900 Bobtail Member

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    Ok, understood. At this point it looses power bobtail and is shutting off with regularity at idle. So any long red light or idling long for any reason and the truck is likely to shut off. None of the shops I’ve been to have seen this issue before or so they say. I try to stick with the same shop until they seem to give up then it’s on to the next one. I’m going on six shops now, smh. They all seem to know what they’re talking about until all the things we try are to no avail. Literally all that’s left to change is the injectors(which I’m not looking forward to), the fuel lines(which I don’t think are bad), and the wiring harness. After that, I’ll park the truck and save some funds and I’m pulling out the Cummins and putting something yellow in. This high pressure fuel system is starting to get on my nerve.
     
  10. OutlawW900

    OutlawW900 Bobtail Member

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    So update........ Today I showed up and there was a great deal of procrastination about doing anything else to the truck. I think might bite the bullet and take it to Cummins at this point.
     
    Oxbow Thanks this.
  11. OutlawW900

    OutlawW900 Bobtail Member

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    Today I had a Cummins tech look at the truck and........ Without me telling him anything he ran the fuel leakage test(turn on the truck at idle pressure stabilized at a little over 8k psi then he shut off motor and left ignition in on position) fuel pressure dropped down faster then a plane with no wings. He rechecked my fuel rail check valve to make sure it wasn’t leaking afterwards it was concluded that it was the injectors. We didn’t even bother checking which one since is best to change all when one goes bad.
     
    Goodysnap Thanks this.
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