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89 Navistar 7.3 idi----Learner Question

Discussion in '6.9L IH & 7.3L IDI Diesels' started by hrsitton, Jan 11, 2019.

  1. hrsitton

    hrsitton Registered User

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    Should there be a fuel flow in the return line from the IP with the electronic fuel pump running and ignition switch at run position but engine not running?

    Thanks, Harold
     
  2. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

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    Nope, there is no direct path from the inlet of the pump and the return unless the engine is rotating.
     
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  3. Clb

    Clb Another old truck Supporting Member

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    Would the returns routing have some influence here?
    been up way to long before sunrise today to think it thru...

    Edit
    Wes is right, from the return on the i.p.
    Nothing SHOULD flow eng. with Off.

    There will be back pressure in the lines...
    This goes back to the e pump convo. Where the dash light comes on..
    Talking about a residual valve.
     
    Last edited: Jan 12, 2019
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  4. chillman88

    chillman88 Supporting Member Supporting Member

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    Depends on WHERE you are looking. I'm going to assume Wes is right about the IP, he knows far more about them than I ever will however...

    Stock there is a feed from the filter head into the return lines. If you are looking anywhere other than the outlet of the IP while unhooked from the rest of the system you could be seeing flow from that.
     
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  5. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

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    Yep, I was just referring to the ip, there’s a 5 psi regulator in the filter head that will bleed off some excess pressure to the return, although usually are clogged and can’t open. If you want to check to see that your e pump is working depress the schrader valve in the filter head
     
  6. hrsitton

    hrsitton Registered User

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    Ok, went to sleep thinking about this. I had in my head that there was a right bank return and left bank return with one out of the filter and one out of the IP.

    Now I see they are two independent returns. The one at the filter has just a jet or small opening that bleeds off excess fuel and pressure from the (brand new Facet Duralift 5-7 PSI). The filter bypass hose is clear so the pump is working with no air bubbles. And there is a fuel pressure gauge inline with the pipe to the IP that stands steady at 4 PSI.

    And now I understand (i think) that the IP return is a return for excess fuel pumped by the IP.

    Two return lines, one for each pump, the lift and the IP.

    So now I would like to test if the IP is actually receiving fuel.

    If the fuel return line is disconnected from the IP and ran into a container, there should be fuel deposited during cranking, right?

    I've checked the connections on top of the IP and they have voltage with the ignition switch in the run position. And a hot wire running to the spades causes a clicking on both terminals so seems the FSS is working.

    To verify I'll try monitoring the IP return and that should tell more of the story.

    Thanks a lot for verifying no fuel from IP return unless engine is turning. Now I (duh) understand. If the pump is not turning, can't be any return.

    It's 4 AM and I'm waking up.
     
  7. franklin2

    franklin2 Full Access Member

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    Assuming you are working on a engine that will not run? Another way to verify fuel is to look at the tailpipe while you are cranking. If you are getting a lot of white stinky smoke out of the tailpipe, you are getting fuel to the engine.
     
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  8. hrsitton

    hrsitton Registered User

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    @franklin2

    Yep. No start condition. Zero white smoke or any smoke out the tailpipe. I learned about the white/lean smoke a few years ago when the mechanical pump went out. Camping in the National Forrest at the time. That turned into a fun adventure.

    This is an 89 U-haul converted to a MH/Funmover.

    I'm suspecting no fuel to engine at all. Engine started in less than one revolution 4 years ago when it was parked.

    Since then it burned one glow plug completely out while sitting. How'd that happen I have no idea. All 8 replaced new and have 12 seconds on the WTS light again where was down to 1-2 seconds.

    When it get's above freezing outside and the sun peeps over the mountain, I'll check if there is fuel in the IP return while cranking. If none, I'll jumper to the FSS and try again.

    I read somewhere that all circuits are killed except the starter and FSS when cranking. Maybe the FSS is turning off when cranking too for some unexplained reason.

    Truck has a good motor and there is no reason not to start if getting fuel and glow plug heat.......unless it's been tampered with which is actually a possibility.

    Edit: Since there is no smoke at all, I guess I can just conclude no fuel to the engine. But the solenoid clicks. Maybe it's just trying to open? I'll put a jumper on so it'll for certain be getting power during cranking.
     
    Last edited: Jan 12, 2019
  9. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

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    Is it cold enough for fuel to gel? The proper way to check that the injection pump is getting fuel is to crack open on of the injection lines and turn the engine over. Look for wetness and some bubbling, the pump will return fuel even if it’s not injecting anything. How fast is it spinning when you crank?
     
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  10. hrsitton

    hrsitton Registered User

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    @Thewespaul

    No gel, it's 30F right now. Never gets cold enough here for gel.

    Brand new interstates same as U-haul had in it. Absolutely whirls the engine. Feels like I could drive on the battery.

    Ok got it. I do not know the innards of the IP so I get it that once the IP is spinning the return can be flowing but the lines not getting fuel injected into them, or something like that.

    So I'll crack one (a couple turns?) and give it a 10 second start and see what happens.

    Hmmm, but wouldn't a return line flow at least prove the FSS was opening? Or no?
     
  11. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

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    If the truck spins over good (more than 250 rpms) then the fss isn’t shutting off when you load the batteries, the fss only needs 4.5 volts and if your voltage was dropping that low the starter wouldn’t spin. The pump can return fuel with the fss not activated, the only sure fire way to to crack an injection line open.
     
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  12. hrsitton

    hrsitton Registered User

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    THAT is what my thick head needed to understand. So the FSS must just open a circuit to the cylinder delivery circuit.

    Since there is no smoke nor any hint of firing, FSS is suspected but will do the cracked line test to be for certain.

    Thanks a bunch!
     
  13. Oledirtypearl86

    Oledirtypearl86 Full Access Member

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    I was reading this and something that stood out was it sat for a few years is there a chance you grew some algy and that is plugging your system up
     
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  14. hrsitton

    hrsitton Registered User

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    @Thewespaul

    Loosened one fuel line connector at one injector a full two turns. Waited for the WTS light and cranked 10 seconds.

    Not a drop at the connection. Inspected the clear IP return line at the bottom barb connection for puddling there and saw none.

    There was a steady 4 PSI at the pipe to the IP and the Schrader vave and filter return was checked for air, there was none.

    So does this mean the IP pump along with one glow plug died while resting?



    @Oledirtypearl86

    Don't know about the algae. It seems to be a controversial subject on the internet search.
     
  15. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

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    Theres two prongs on the top of the injection pump, with the key on disconnect the front prong and reconnect it. You should hear a loud click when reconnecting it, if you dont check your fuses.
     

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