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Thread: Troubleshooting Lift Pump

  1. #1
    Join Date
    Mar 2009
    Location
    Folsom, CA
    Posts
    194

    Default Troubleshooting Lift Pump

    Okay, I have the motor in but I don’t have fuel to the filter. I suspect the lift pump. Should I be getting a straight 12v to it? Before I pulled the motor I would hear it rattling occasionally. Is the rattle normal or was it on the fritz then? It is a relatively new lift pump.

    Thanks

    Mike
    Mike
    1994 K2500 Suburban 316,000 mi., F VIN, 4L80E, 3.73 w/posi., 3" turbo back, no cat, FSD Heat Sync, #9 resistor, SSD heads, SSD intake, fuel miser injectors, Bastard IP (5068), 4x4 posi, Cooling upgrade w/duel 180° t-stats and d-max fan

  2. #2
    Join Date
    Feb 2007
    Posts
    2,926

    Default

    The system that year is a bad design, the pump does nothing until you operated the starter, or there is oil pressure. To get fuel through to the filter, remove the black plastic cover on the fire wall, 2 nuts holding it, pull out the fuse, and connect a wire from the live threaded post, to the fuse holder, the pump will run. The pumps are noisy.
    Grant H.
    1995 6.5 turbo GMC K2500 extra cab 4x4 pickup, PMD under bumper, mechanical wastegate, 228,000 miles, rebuilt engine, 4.10 diff, 16 mpg
    1994 6.5 turbo GMC K2500 4x4 suburban #9 resistor, PMD in the bumper, mechanical waste gate, 226,000 miles, 3.73 diff, 16 mpg
    1982 4x4 shortbed 6.2 Chev 260,000 miles untouched motor 17 MPG 4.27 diff. Best thing I ever owned, since 1992.

  3. #3
    Join Date
    Mar 2009
    Location
    Folsom, CA
    Posts
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    Default

    Thanks Grant, I’ve now done that I have fuel pressure to the IP and the motor cranks but I’m not getting fuel to the injectors. I’m thinking maybe fuel shutoff solenoid. I’m still learning exactly how these IPs work. What activates the shut off solenoid?
    Mike
    1994 K2500 Suburban 316,000 mi., F VIN, 4L80E, 3.73 w/posi., 3" turbo back, no cat, FSD Heat Sync, #9 resistor, SSD heads, SSD intake, fuel miser injectors, Bastard IP (5068), 4x4 posi, Cooling upgrade w/duel 180° t-stats and d-max fan

  4. #4
    Join Date
    Feb 2007
    Posts
    2,926

    Default

    The shut off solenoid opens when the the ignition is on, have someone turn the key on and off and listen for the click or feel for it. You can remove it, take the needle out and put the valve back in. Turning the key off when the engine is running will shut the ECM, down, so the shutoff is an extra. Have you got 2 injector nuts loose, to let the air out of the IP? Turn the ignition on and jumper that fuse to make the lift pump run, this opens the air bleed on the IP, to flush the air out.
    Last edited by grancito; 07-24-2020 at 04:23 PM.
    Grant H.
    1995 6.5 turbo GMC K2500 extra cab 4x4 pickup, PMD under bumper, mechanical wastegate, 228,000 miles, rebuilt engine, 4.10 diff, 16 mpg
    1994 6.5 turbo GMC K2500 4x4 suburban #9 resistor, PMD in the bumper, mechanical waste gate, 226,000 miles, 3.73 diff, 16 mpg
    1982 4x4 shortbed 6.2 Chev 260,000 miles untouched motor 17 MPG 4.27 diff. Best thing I ever owned, since 1992.

  5. #5
    Join Date
    Mar 2009
    Location
    Folsom, CA
    Posts
    194

    Default

    So here it is, I’m able to jump the lift pump and hear it run. The motor cranks over pretty well and I loosened several injector lines to bleed any air. As I crank it over I am getting raw fuel out the exhaust and it will occasionally stumble like it’s trying to light but it won’t. As it sits after cranking some fuel vapor will come out the turbo (I’m doing this without the air filter on). I checked and rechecked the injector lines at the IP before I put the lower intake back on but I’m thinking this might be the issue. Is it possible I’m missing something else?

    Thanks
    Mike
    1994 K2500 Suburban 316,000 mi., F VIN, 4L80E, 3.73 w/posi., 3" turbo back, no cat, FSD Heat Sync, #9 resistor, SSD heads, SSD intake, fuel miser injectors, Bastard IP (5068), 4x4 posi, Cooling upgrade w/duel 180° t-stats and d-max fan

  6. #6
    Join Date
    Feb 2007
    Posts
    2,926

    Default

    Good you have fuel to the injectors. Next, are you getting enough glow plug time, 8 seconds? The other, is did you time the cam shaft correctly, and is the Injection pump near correct timing? When it stumbles and tries to start, tighten the loose injector nuts, these ones will help it start.
    Last edited by grancito; 07-25-2020 at 12:30 AM.
    Grant H.
    1995 6.5 turbo GMC K2500 extra cab 4x4 pickup, PMD under bumper, mechanical wastegate, 228,000 miles, rebuilt engine, 4.10 diff, 16 mpg
    1994 6.5 turbo GMC K2500 4x4 suburban #9 resistor, PMD in the bumper, mechanical waste gate, 226,000 miles, 3.73 diff, 16 mpg
    1982 4x4 shortbed 6.2 Chev 260,000 miles untouched motor 17 MPG 4.27 diff. Best thing I ever owned, since 1992.

  7. #7
    Join Date
    Mar 2009
    Location
    Folsom, CA
    Posts
    194

    Default

    I didn’t touch the bottom end when I had the motor out, just a visual inspection, and I left the IP alone, too. Just to be sure, I turned it over by hand in the stand after everything was put together.

    Today, I only bled about half the injectors so I may bleed the rest tomorrow. I haven’t checked the glow plugs and I know these motors need them in all conditions but it’s pushing 100° during the day here and I would have figured it would have come closer to starting even if they’re not cycling properly. For what it’s worth it fired right up prior to rebuild, even with a bad valve.
    Mike
    1994 K2500 Suburban 316,000 mi., F VIN, 4L80E, 3.73 w/posi., 3" turbo back, no cat, FSD Heat Sync, #9 resistor, SSD heads, SSD intake, fuel miser injectors, Bastard IP (5068), 4x4 posi, Cooling upgrade w/duel 180° t-stats and d-max fan

  8. #8
    Join Date
    Feb 2007
    Posts
    2,926

    Default

    There is no need to bleed all of the injectors, 2 is enough. The glow plugs are needed on engines with poor compression, even when they are almost at running temperature. I guess you changed the rings, so the cylinder pressures will be low. As you have not made any timing changes, the symptoms are lack of glow plug time, or function. Did you put a test meter on each plug, I found one had failed on my engine, the one that was not accessible until the engine was removed. Work on that, it will then start, even if you have to make a temporary jumper to activate the relay.
    Grant H.
    1995 6.5 turbo GMC K2500 extra cab 4x4 pickup, PMD under bumper, mechanical wastegate, 228,000 miles, rebuilt engine, 4.10 diff, 16 mpg
    1994 6.5 turbo GMC K2500 4x4 suburban #9 resistor, PMD in the bumper, mechanical waste gate, 226,000 miles, 3.73 diff, 16 mpg
    1982 4x4 shortbed 6.2 Chev 260,000 miles untouched motor 17 MPG 4.27 diff. Best thing I ever owned, since 1992.

  9. #9
    Join Date
    Mar 2009
    Location
    Folsom, CA
    Posts
    194

    Default

    Update:
    Even though I double checked (and it’s hard to mess up) I pulled the intake to check injector timing... Everything looks good there.
    Engine still turns over well, I have decent fuel pressure to IP and it will puff raw fuel.
    I jumped the glow plug relay for about 10s prior to turning over and it didn’t seem to make a difference (the relay seems to working Okay)

    I did not do rings While apart but again it ran okay before I pulled it.

    So are you saying one bad glow plug will keep it from starting?
    The glow plugs aren’t that old but if I’d know that I would have replaced them.
    Mike
    1994 K2500 Suburban 316,000 mi., F VIN, 4L80E, 3.73 w/posi., 3" turbo back, no cat, FSD Heat Sync, #9 resistor, SSD heads, SSD intake, fuel miser injectors, Bastard IP (5068), 4x4 posi, Cooling upgrade w/duel 180° t-stats and d-max fan

  10. #10
    Join Date
    Mar 2009
    Location
    Folsom, CA
    Posts
    194

    Default

    One new development since this morning... it appears I can prime the lift pump to about 5psi at the IP but without cycling the engine it will drop to almost 0psi and I’ll see vapor coming out the turbo plus it appears my crankcase oil level is rising all points to I am leaking fuel. Is it possible I have 1 or more injectors stuck open. If so does the IP bleed out fuel or is this an indicator of some other issue? These are brand new injectors and I was very careful to keep them clean.
    Mike
    1994 K2500 Suburban 316,000 mi., F VIN, 4L80E, 3.73 w/posi., 3" turbo back, no cat, FSD Heat Sync, #9 resistor, SSD heads, SSD intake, fuel miser injectors, Bastard IP (5068), 4x4 posi, Cooling upgrade w/duel 180° t-stats and d-max fan

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