ISX15 2350 oil pressure acting strange

Discussion in 'Trucks [ Eighteen Wheelers ]' started by skman, Dec 1, 2023.

  1. skman

    skman Light Load Member

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    Just got truck back from rebuild. Was test drove and was good to go. I bobtailed home...everything was good. Oil pressure up around 40-45 at highway speed @ 1500rpm.
    Hooked to a tanker today and drove about 15 miles and suddenly my oil pressure was at 30psi. Pulled into loading facility and stopped at office. Started driving and my oil is at 40psi again.
    Got loaded and drove about 10 miles and it's down at 28psi again (60mph @ 1500).
    Pulled into fuel station (15psi at dead idle) and popped hood and everything was dry. I checked the oil and it was good. Started up the truck again and now it's at 25psi at dead idle and back to 40-45 at highway speed.
    It continued to do this for the next hour until I got unloaded and got home.
    Then I bobtailed back to the mechanics shop (about 25 miles)...and oil pressure was perfect the whole time.
    I was thinking oil pressure sensor but why doesn't it do it when I was bobtailing? Oil pump (shimmed up) and oil cooler both new with rebuild.
     
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  3. 201

    201 Road Train Member

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    It's clearly something while under a load. Gauges do goofy things, but being a new rebuild, I'd suspect something in the filters.
     
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  4. Goodysnap

    Goodysnap Road Train Member

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    Sensor failure is not uncommon. Inspect for oil wicking into the electrical connector thru the sensor.

    Then a mechanical gauge should be installed and check pressures before and after filter. Sounds very erratic.

    New cam bearings and rods/mains?
     
  5. skman

    skman Light Load Member

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    Yes all new internals except crank. New head, camshaft, injectors, rockers, cooler, pump, and did front structure at the same time
     
  6. kwcam

    kwcam Light Load Member

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    I would try changing the oil filter first, easy and cheap to do, after a fresh rebuild we use to change them out after a few hours at one shop I was at.
    I don't care for the Fleet Guard filter as they don't have much capacity in the primary filtration side, more by-pass filtering When at the dealership we seen some issues over this. we use Lurberfinder . LFP9000 now. If this is a Peterbilt check the ground wire connections at the left front cab mount area, we have seen erratic gauge issues in the past from poor grounds.
     
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  7. skman

    skman Light Load Member

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    Thanks. It's sitting outside the shop now. Will be going back in tomorrow. He did order a sensor but it's intermittent so it'll be hard to tell what fixes it...unless he can see something in Insite. I'll mention to check the wiring where you suggested though. Thanks!
     
  8. pushbroom

    pushbroom Road Train Member

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    If it got a new pump on it the pressures can be different from what they used to be. The new pumps also dont use shims anymore either.
    I still suspect sensor issues but thought it was worth mentioning.
     

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  9. skman

    skman Light Load Member

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    Aug 26, 2013
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    So I got the truck back yesterday. Of course it runs fine in the shop so putting it on the computer didn't really show anything.
    They did change oil pressure sensor. Also (when I did the rebuild) I sent injectors in for testing. 2 passed and were re-used. But one of those 2 are returning back too much and causing an spn 157.
    Today I took the truck out hoping the leaky oil sensor had been the problem. It wasn't.

    I did find out the following yesterday:

    It runs at about 40 or so until oil temp hits approx 212-213. As soon as it hits that temp....you can watch the pressure drop off to 28psi.
    It doesn't change as you drive...even if oil temp drops to 200F...it will stay about 28-30.
    BUT...if it drops under 210F and I make a stop at stop sign and then take off again....the oil pressure comes back up to 40+.
    As soon as it hits over 212F...it drops off again. It does NOT throw any codes when the oil PSI issue happens.

    Also, now I'm getting code 95 instead of 157 while accelerating loaded. Injector hasnt been replaced yet...so that's probably where that code is coming from.

    I'm going to try changing oil filter... just in case. It's a fleetguard on there right now.
     
    Last edited: Dec 9, 2023
  10. olddog_newtricks

    olddog_newtricks Medium Load Member

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    I bought a rebuilt ISX and had basically the same problems you are describing. Turns out the rebuilt motor had metal shavings in it and it spun the bearings. When you change that oil filter , I would cut it open and check for metal. Warranty covered my motor... I made them give me a different one. Even the new one keeps low oil pressure. According to Cummins ... 32 -35 psi is normal under load and anything above 18 is good at idle. Mine keeps 32 -33 and 21 at idle . I've put 180k on it and no problems yet.
     
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  11. skman

    skman Light Load Member

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    Saskatchewan
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    Yeah we shimmed up the pump to run a bit higher pressure. I read the new style pump is less pressure and we run heavy weight so I wanted to at least have what I had before the rebuild.
     
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