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Thread: Lift Pump power 94 3500HD ?

  1. #21
    Join Date
    Dec 2003
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    Yukon Canada
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    Yesterday
    changed the OPS and now have power from it,but no ground at lift pump still.
    I think the actual OPS should have been grounded to get proper gauge operation while it was on my test rig.
    Brought up to operating temp.Unplugged the temp sensor while at operating temp and the engine changes RPM and sound,so that appears to be working.
    Will restart warm without glow plugs or lift pump within a few minutes of shutdown
    Wait 15 minutes and nothing.I can feel and hear the shutoff solenoid when at operating temp when i have the switch cycled or if the switch is on and i unplug it.
    Head scratcher...
    Is there any other electrical component that could heat soak while the ignition switch is off that would interrupt the IP function?
    Thanks Again
    90 Chev 3500 c/c 4x4,6.2na,400 auto,4:10 gears.DSG Timing gears,main girdle, isspro tach, pyro,boost,oil and trany temp.Dual Tstats, High volume peninsular pump,on shelf, Custom turbo and intercooler 85%complete. Change of plans for the dually, it's going to get a Cummins. Both trucks are Blue 90 4x4 crews

  2. #22
    Join Date
    Dec 2003
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    Yukon Canada
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    Spent a couple days without being able to try anything on the truck
    Yesterday i had it in a no start condition.I cooled the IP with liquid propane and it started up.
    Wanted to replicate it when a new problem arose, bad connection on the starter system and it was just clicking.
    Fingers crossed that fixing the loose connection may solve some issues.
    Once i fix the loose connection i will replicate my test to see if i get the same results.
    If i do i am assuming that i will have to change the IP, being a 94 i believe the options to replace the IP is limited to 94 year only.
    Thanks all that have given me ideas to try.
    90 Chev 3500 c/c 4x4,6.2na,400 auto,4:10 gears.DSG Timing gears,main girdle, isspro tach, pyro,boost,oil and trany temp.Dual Tstats, High volume peninsular pump,on shelf, Custom turbo and intercooler 85%complete. Change of plans for the dually, it's going to get a Cummins. Both trucks are Blue 90 4x4 crews

  3. #23
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    Dec 2003
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    Yukon Canada
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    I finished off a project that i had in my shop, and brought the 3500 in and put it on the hoist to clean up a few items.
    I was able to trace the ground wire for the lift pump.
    For some reason GM grounds the lift pump to somewhere at the back of the frame by the fuel tank.Soldered the broken wire, now the only issue is the no start after a heat soak.
    90 Chev 3500 c/c 4x4,6.2na,400 auto,4:10 gears.DSG Timing gears,main girdle, isspro tach, pyro,boost,oil and trany temp.Dual Tstats, High volume peninsular pump,on shelf, Custom turbo and intercooler 85%complete. Change of plans for the dually, it's going to get a Cummins. Both trucks are Blue 90 4x4 crews

  4. #24
    Join Date
    Apr 2001
    Location
    CA
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    13,573

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    Quote Originally Posted by Yukon6.2 View Post
    I finished off a project that i had in my shop, and brought the 3500 in and put it on the hoist to clean up a few items.
    I was able to trace the ground wire for the lift pump.
    For some reason GM grounds the lift pump to somewhere at the back of the frame by the fuel tank.Soldered the broken wire, now the only issue is the no start after a heat soak.
    The ground location is universal with the gasser counterparts, with the fuel pump in the tanks. We like the Diesels, but the majority of models were not Diesel. They probably saved a million or three avoiding the engineering and tooling accommodations.
    1985 Blazer 6.2
    2001 GMC 2500HD D/A
    dmaxmaverick@thedieselpage.com

  5. #25
    Join Date
    Dec 2003
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    Yukon Canada
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    It ends at a bolt through the left rear frame rail.
    My plan was the same but 6" from the pump
    They could have saved 10 ft of wire with my change order that didn't go through.
    90 Chev 3500 c/c 4x4,6.2na,400 auto,4:10 gears.DSG Timing gears,main girdle, isspro tach, pyro,boost,oil and trany temp.Dual Tstats, High volume peninsular pump,on shelf, Custom turbo and intercooler 85%complete. Change of plans for the dually, it's going to get a Cummins. Both trucks are Blue 90 4x4 crews

  6. #26
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    Apr 2001
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    Newberg Oregon
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    Reading over this issue......
    Once the engine gets up to temperature EVERYTHING expands a little.....Including the Plunger bores in the Injection pump.

    How old (Miles on the IP) ?????
    When was the fuel filter last changed ????

    A hard / no start on a warm engine can be related to NOT ENOUGH PRESSURE BEING MADE in the IP to pop the injectors

    GET A GLOW PLUG ON THE DRIVERS SIDE OUT and spin the engine....see if fuel mist blows out......

    If fuel blows out it should run....especially when warm.

    NO fuel at glow plug hole..... WHY ?????
    IP WORN OUT...
    FUEL SHUTOFF SOLENOID FAILURE....

    The fact that the engine will start from cold and run OK indicates that the systems SEEM to be functioning.....

    An electronic components failure SHOULD show issues while the engine is running...

    A short shut down should NOT cause an issue

    My suspicion is the IP is just not making POP pressure....

    The reference on the SOL D unit was correct.....The unit would not lite the fire when it was cold and line voltage dropped off....

    Jump the rig with some big batteries and BOOM lite right off.

    SOL D never addressed the issue and faded into the mists of time and 6.5 history.....


    I have started a few 6.5 with low crank speed.....Computer does not care so much about speed.

    Cranking speed has more to do with getting compression in the cylinders up .....And if the IP is worn ....a low speed will simply not get the pressure in the plungers up to pop level....


    When it is warm and will not start....Yank a plug...roll it over and see wasssssup
    (1) 1995 Suburban 2500 4x4
    (1) 1997 Astro
    (1) 2005 Suburban (Papa Smurf)
    THIS IS BOW TIE COUNTRY

  7. #27
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    Apr 2001
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    Newberg Oregon
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    Another thing

    These rigs have two points that the positive battery feed connects..

    Early GMT400 trucks fed the RH battery to the starter and to the junction box on the firewall
    The LH battery was connected to the alternator and to the cross connect cable between the batteries....

    Later Rigs connected the RH battery to the starter ...The LH battery to the relay box on the driver inner fender....The alternator connects to the LH battery
    Cross connect is similar.

    THE GM BATTERY CABLES are crap.....Crimped connections on the side terminals.....IT IS VERY COMMON to see the cables corroded down in the strands of wire..

    Same with the ground cables....JUST BECAUSE THE CABLE ENDS ARE CLEAN....Does NOT mean the circuit is good.

    I have seen grounds on these that looked perfect....but when the cable was dissected were just nasty.

    The cross connect cable is also suspect too.....You can have connection all the way.....but once the load is put to the system the voltage and amperage goes in the toilet

    Check with the engine running and see what the voltage is at each battery.

    14.5 volts is good.....It is common to see the LH battery (Alternator connected) at 14.5 and the RH battery at 12.5 or so.....

    Used cables are suspect......They can't be examined without cutting the insulation jacket......I have seen the ground on one battery absolutely dead ZERO ZIP NAPA and the other one good....

    CHECK THE VOLTAGE....The system voltage at the relay box lug should be 14.5 running....

    There should be very similar voltages at each battery....Alternator lug and the main power lug in the relay box...

    Any odd ducks are a sign that cables are to blame.....

    The only cables that are close to satisfactory are ones that have the copper eye soldered onto the cables and all the strands in the solder.....
    All crimped battery cables will corrode over time....and you can't see it...
    (1) 1995 Suburban 2500 4x4
    (1) 1997 Astro
    (1) 2005 Suburban (Papa Smurf)
    THIS IS BOW TIE COUNTRY

  8. #28
    Join Date
    Feb 2000
    Location
    Montana
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    When one of these engines won't start after sitting for 30+ minutes, it's usually due to one of a few items (not necessarily in any order):
    1- Poor fuel atomization.
    2- Slow cranking speed.
    3- Low cylinder compression.
    4- Injection timing.
    5- Cam timing.
    and maybe others... always begin your troubleshooting by eliminating the cheapest/easiest possibility first.

    Generally, these engine will start normally without glow heat down to less than about 80 degrees F. As an aside... Sarah's 1994 6.5TD Blazer is running an aftermarket PCM chip. This chip glows the glow plugs hot or cold. It's either a Heath or Kennedy chip.

  9. #29
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    I am pretty convinced it must be the injection pump.
    When it doesn't start i can cool the head of the pump with liquid propane for 20 seconds and it fires right up.
    The rest of the health of the pump masks the heat soak.
    It starts and runs without the lift-pump,drives good no hesitation on WOT, and no codes
    90 Chev 3500 c/c 4x4,6.2na,400 auto,4:10 gears.DSG Timing gears,main girdle, isspro tach, pyro,boost,oil and trany temp.Dual Tstats, High volume peninsular pump,on shelf, Custom turbo and intercooler 85%complete. Change of plans for the dually, it's going to get a Cummins. Both trucks are Blue 90 4x4 crews

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