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Thread: Troubleshooting Lift Pump

  1. #31
    Join Date
    Feb 2007
    Posts
    2,926

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    From memory, a bad crank sensor will give a no start, but the engine will start without it connected. When you said the engine turns over "not so rough" with the ECM fuse out, you are describing uneven compression. It must be the valves not opening properly. Try a google search, someone on diesel place may have the answer to unprimed lifters.
    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.

  2. #32
    Join Date
    Mar 2009
    Location
    Folsom, CA
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    194

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    Ive got the valve covers off. What is the best way to turn over the motor to troubleshoot? Keeping in mind everything is disconnected. Also, should I be able to twist any of the pushrods or are they under constant pressure?
    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

  3. #33
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    Feb 2007
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    You should be able to turn some of the push rods. Check if any push rods have up and down movement, push down on the rod end of the rocker to check for a spongy feeling. I ran mine with the covers off, so some assembly was necessary. You could remove the ECM fuse, and nudge the engine over on the starter, then check the rockers again, when the cam is in a different position.
    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.

  4. #34
    Join Date
    Mar 2009
    Location
    Folsom, CA
    Posts
    194

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    So I’ve turned over the motor by hand and checked each rocker. None are spongy. I cannot seem to spin any of the push rods by hand. Each rocker has about 1/2in of travel top to bottom. There is a little side to side that I can wiggle some of the rockers but not much. All my valve retainers are in place. All rocker retainer buttons are in place. All eight rocker bolts are tight.
    By the way, which direction does the engine spin?
    Last edited by CAdiesel; 08-09-2020 at 05:15 PM.
    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

  5. #35
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    Feb 2007
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    It spins clockwise, the air out the intake sounds bad. There is an exhaust port on the intake side of each head, for S vin engines to recirculate exhaust gas. Did you replace the heads or just some valves?
    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.

  6. #36
    Join Date
    Mar 2009
    Location
    Folsom, CA
    Posts
    194

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    I checked by putting aluminum foil over the intake ports and it seems all are pulling vacuum. So that’s a relief.

    I replaced one head completely and all the exhaust valves only in the other. I lapped all the valves (intake and exhaust) in the existing head before reassembly.

    I’m in the process of checking compression but it seems I have to crank the motor with the starter for it to work. I was hoping I could get something by hand but that doesn’t seem to be the case.
    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

  7. #37
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    Feb 2007
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    Yes you need the starter for a compression test. Hopefully you didn't lap the valves in a lot, the lifter tolerance is limited, but I can't remember where the measurement of protruding valve stem is found. I'll check my papers in the workshop to see if it is listed.
    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.

  8. #38
    Join Date
    Mar 2009
    Location
    Folsom, CA
    Posts
    194

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    10-4 on the starter.

    I lapped them by hand, in fact I had my kids help. (This has been a Covid project.) So let me know what “too much” is. I’d be surprised if I was there.

    I’ll report back after I check compression and clean up the mess.
    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

  9. #39
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    Feb 2007
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    I don't have the spec for the valves, only read it and didn't save it because I had new heads and block. The valve grind should not be a problem, as no machine cutting was used. If you find compressions on one side of the engine low, put shims made from a can between the rocker shaft and posts to lift the rockers up off the valves, and test again, this will tell you if the valves are not closing properly.
    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.

  10. #40
    Join Date
    Mar 2009
    Location
    Folsom, CA
    Posts
    194

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    When I went to check compression I had 0psi on cyl 1. When I pulled the rocker assembly off I got about 180psi. So it appears that my valves are not closing properly. I replaced the push rods rockers and lifters during my overhaul. Push rods and rockers are the same as the old ones and I believe I checked the lifters before putting them in. Is the hydraulic lifter supposed to give some and it isnt? Are they somehow seized?
    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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