What shouldmy fuel pressue be at?

Discussion in 'Peterbilt Forum' started by irishluck09, Mar 26, 2020.

  1. Mar 26, 2020 #1
    irishluck09

    irishluck09 Light Load Member

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    1996 peterbilt 378 with 3406e

    Past few days my truck hs been bogging down at about 1700-2000 rpm. Cant get above 50mph. Assuming its my fuel filters.

    If my fuel psi gauge is working right, at idle it sits at about 32psi. High idle, 45psi. And when driving under load, about 5psi. Assuming 5 psi is a bit low right?
     
    irishluck09, Mar 26, 2020
    irishluck09, Mar 26, 2020
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  3. Mar 26, 2020 #2
    062

    062 Road Train Member

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    Not sure what the spec is, but 5psi isn’t right. You need to hook up another gauge to get a good reading. My guess is factory is 50-70 psi.
    @spsauerland @pushbroom can give you the right number.
     
    062, Mar 26, 2020
    062, Mar 26, 2020
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  4. Mar 26, 2020 #3
    stillwurkin

    stillwurkin Road Train Member

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    Change fuel filters to start. Restriction guage reads off primary filter. My guage from 2 to 8 is in the green. But should run at appprx 5 give or take. 5 to 6 even when pulling. How long since you changed filters?
     
    stillwurkin, Mar 26, 2020
    stillwurkin, Mar 26, 2020
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  5. Mar 26, 2020 #4
    irishluck09

    irishluck09 Light Load Member

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    I just bought the truck on November. I havent changed and no idea when the last owner did it.

    This is a picture of my gauge at idle
     

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    irishluck09, Mar 26, 2020
    irishluck09, Mar 26, 2020
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  7. Mar 26, 2020 #5
    pushbroom

    pushbroom Road Train Member

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    If its reading correctly is way too low.
    I would start by verifying it with another guage first. 75psi minimum idling and 90psi cruising speed or around there.
     
    pushbroom, Mar 26, 2020
    pushbroom, Mar 26, 2020
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  8. Mar 26, 2020 #6
    irishluck09

    irishluck09 Light Load Member

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    Well i went ahead and changed out the fuel filter (the screened one) which was just covered in dirt. So assuming that wasmy issue.

    Now i jusycant get the truck started. Been trying to prime with the pump. Used 2 cans of starter fluid and it just wont stay running by itself.

    Is there a trick im missing here? Both filters are full of diesel
     
    irishluck09, Mar 26, 2020
    irishluck09, Mar 26, 2020
    #6
  9. Mar 26, 2020 #7
    062

    062 Road Train Member

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    Do you have a way to put air in fuel tank?
     
    062, Mar 26, 2020
    062, Mar 26, 2020
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  10. Mar 26, 2020 #8
    irishluck09

    irishluck09 Light Load Member

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    Unfortunately no. Shes being towed
     
    irishluck09, Mar 26, 2020
    irishluck09, Mar 26, 2020
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  11. Apr 1, 2020 #10
    irishluck09

    irishluck09 Light Load Member

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    So come to find out, it was my lift pump that went bad. Put new one on and this truck has never run so good. 75psi idle. 90 under load. Even went from 3.5mpg to 5.5mpg
     
    irishluck09, Apr 1, 2020
    irishluck09, Apr 1, 2020
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    pushbroom and 062 Thank this.
  12. Apr 5, 2020 #10
    HoneyBadger67

    HoneyBadger67 Road Train Member

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    Mine works just the opposite way. It measures restriction, I guess, and have only seen it in the red one time and I changed the filters. I really want more gauges in this truck (egt, fuel pressure, maybe a couple others) but there isn't any place to put them. Not to mention I might or might not be smart enough to install them. 15861334856055809494049113770555.jpg
     
    HoneyBadger67, Apr 5, 2020
    HoneyBadger67, Apr 5, 2020
    #10
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