TBI surging

Discussion in 'Engine Performance + Maintenance' started by RustyShackleford, Apr 17, 2021.

  1. RustyShackleford

    RustyShackleford Newbie

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    90 k1500 5.7 TBI
    I’m trying to get this truck running right for my uncle. It’s an old farm truck that he has had for many years. Back around January he put about 2 gallons on tractor hydraulic fluid in the gas tank because it was in a gas jug. Doh! He has run 2 tanks of gas through and changed the fuel filter since then.
    I have replaced the TB gasket, cleaned TB, replaced IAC, and put a new O2 sensor on because the wire on the old one was broken. He says the truck has been running rough since before the hydraulic fluid incident, but it is getting worse and worse. He thinks it’s the fuel pump. We took the line loose from the TB and turned the key to the “on” position and nothing came out of the line. It only pumps fuel when you crank. I know they’re supposed to have ~12psi. Is it right to only pump when you go past the “on” position with the key? Also, I thought a fuel pump either worked or it didn’t. I haven’t known one to slowly die.
    At any rate, I took a video. The link is below. It’s weird that the fuel cone seems to cut out. Thoughts?

     
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  2. GoToGuy

    GoToGuy OBS Enthusiast

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    Fuel orings and mineral oil (lube) are two different animals. If the spray pattern is abnormal and pressure is adequate is fuel injector damaged from tractor hydraulic fluid? What is tractor base fluid? Time, age wise for complete tuneup with new injectors?
     
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  3. R422b

    R422b I'm Awesome

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    What is the current fuel pressure?
    When I saw your username I had to check where you were located because I had a friend who used the name Rusty shackelford at one point.

    Talking about GMT400s using Tapatalk
     
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  4. HotWheelsBurban

    HotWheelsBurban Burbs are great!

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    So
    So Dale Gribble does exist, and he's on the forum cause he has a Chevy truck. All I remember from King of the Hill was that he had an old Ford....
     
  5. PlayingWithTBI

    PlayingWithTBI Desert Old Guy

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    When you turn on the key with engine off, the fuel pump will run for 2 seconds. Then it'll run again when cranking.

    Edit: If it doesn't prime for 2 seconds with KOEO, you need to check your fuel pump relay circuit. If I had to guess, I'd say your ICM and/or coil are going out causing the ECM to cut off fuel when it doesn't get a signal for the ICM.
     
    Last edited: Apr 17, 2021
  6. Schurkey

    Schurkey I'm Awesome

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    How long has it been since the usual "tune-up" stuff was inspected/replaced/adjusted?
    Distributor cap and rotor
    Plug wires including coil wire
    Test coil output with spark tester calibrated for HEI ignitions
    Set timing with timing wire disconnected
    Verify knock sensor by tapping a small hammer on the intake manifold--should hear change in idle speed as knock sensor retards timing.
    New or cleaned/regapped spark plugs
    Cranking compression test on all eight
    Verify EGR isn't leaking at idle, but does hold vacuum and works at higher speed.

    Connect scan tool to look for "codes" and to verify sensors and outputs using the data stream.

    VERIFY FUEL PRESSURE.
    Spec is 8--13 psi, most folks want to be at the higher end.

    Sounds like the fuel pump isn't priming like it's supposed to. The pump should run for two seconds when the key goes from "Off" to "Run". Then the pump shuts off until the engine cranks. If you turn the key off, and wait a little while, it should prime again when the key is turned to "Run".

    The pump is supposed to be controlled by the fuel pump relay, which itself is controlled by the ECM. There is a second system, that runs the fuel pump when the engine has oil pressure. If you only have fuel when the engine has cranked long enough to generate oil pressure, you've got a fault in the fuel pump relay circuit--faulty ECM, faulty wire harness, and/or faulty relay. Most folks trade relays with some other system, if the pump works with the other relay, they buy a relay and pitch the bad one. But it's not always the relay that's faulty.

    Slow death is more common than sudden failure--unless the problem is in the wire harness or control system.

    The injectors alternate left-right-left-right. Especially noticeable at low engine speed. Totally normal. It might be indicating that your engine idle speed is too low.
     
  7. thinger2

    thinger2 I'm Awesome

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    Yep, hard to tell from the vid but it does seem to have a bit of a stutter.
    I wonder if that injector body filter is part plugged or not seated and getting bypassed from a leak
    Just a little drip will do it.
     
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  8. CrustyJunker

    CrustyJunker Is STILL Here?

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    If he insists it was doing this prior to the hydraulic fluid incident...Might not hurt to check for vacuum leaks around the intake manifold gaskets, too. :waytogo:
     
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