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Important tips on changing a fuel lift pump

Discussion in '1982-Present GM Diesel' started by arveetek, Apr 4, 2003.

  1. arveetek

    arveetek 1/2 ton status

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    Hard starting can often be attributed to a failing fuel lift pump. This mechanical pump is mounted down on the lower, front passenger side of the engine block, in the same place as on the gasser blocks.

    I have changed several pumps, and through trial and error, have come up with the following tips for changing this pump out. When you remove the pump, you allow air into the system, and if you don't follow these steps, you can end up with an air-locked diesel engine, which can be rather frustrating to start.

    These steps apply to 84 and up 6.2L diesel equipped trucks with the Model 80 square fuel filter mounted on the firewall. For 82-83 trucks with the round, spin-on style filters, read the note at the bottom.

    First, drain the fuel filter. On the very bottom right side of the fuel filter assy. is a little plastic valve. Right under this valve should be a barbed hose fitting pointing straight down....it will be hard to see, you can feel it though. There might already be a length of hose attached to this fitting. If not, get a length of hose to help drain the fuel away from the truck and into a pan or something. You don't have to, but it will make a much cleaner job.

    On top of the fuel filter assy. is another small plastic valve directly above a smaller barbed fuel fitting pointing straight out on the left side. This is the air bleed valve. Open this valve, and then open the drain valve on the bottom. This will let the fuel drain out of the filter, down the hose, and into a pan. This will prevent fuel from spilling all over you when you remove the pump.

    After the fuel has drained, start removing the pump by disconnecting the fuel lines. The suction side will have a rubber hose and clamp, the pressure side will have a steel line screwed into the pump. Use a 9/16" line wrench if you can to avoid stripping this fitting. When you remove the suction hose, it may continue to dribble fuel out. If so, shove a 3/8" bolt into that hose to stop it up.

    Next, remove the two mounting bolts holding the pump on. IIRC, you need a 1/2" socket for this. The bolt on the back side of the pump is hard to get to. You can try getting to it from the top side of the motor or from the bottom. I think the top side is just a bit easier.

    Remove the pump.

    Now remove the plunger rod cover by removing the two remaining bolts at the bottom. IIRC, these require a 7/16" socket. You have to remove this plate in order to remove the plunger rod. When you removed the pump, the rod probably fell down. Now you can't get the rod to stay up in place. (This rod rides against the camshaft, which in turn rides against the pump plunger.) Once you remove the cover, slide the rod out. Cover it with thick grease, and shove it back up in the hole. The grease will help hold it in place. There is a chance that the motor shut off in a place where the camshaft lobe is holding the rod out in the extended position. If this happened, it will be next to impossible to install the pump. I suggest you rotate the engine by putting a large socket on one of the front pulley bolts. You can tell when the rod is retracted all the way because it goes way up in there out of the way.

    Clean up the surfaces on the rod cover and the engine block. I like to use Ultra Copper silicone sealant on these parts. Reinstall the cover.

    The pump should come with a gasket. I typically install the gasket along with Indian Head gasket Shellac.

    Install the pump.

    Reconnect the fuel lines.

    Now you have to bleed the fuel system. First, if you haven't recently replaced the fuel filter, go ahead and install a new one. Just undo the clasps and pull straight out on the filter. Put a little oil on the o-rings of the new one when you go to install it. The new just pushes back on.

    Close the drain valve on the bottom of the fuel filter assy, but leave the air valve on top open. Next, disconnect the fuel cut-off solenoid on the injection pump. This is the pink wire right on top of the pump itself. We want to avoid pumping any air into the injection lines when we start cranking the motor, and by removing this wire, the air can't get into them.

    To save battery power and the glow plugs, disconnect all 8 wires going to the glow plugs. (that is if you have an automatic glow system...if yours is manual, then just don't glow!)

    If you can, install a piece of clear tubing over the small barb on the top left of the fuel filter assy. I usually run this clear hose into a container sitting on the cowl of the vehicle so I can see it from the driver's seat.

    Start cranking the motor over. We're not trying to start it, we're just priming the system. What you're doing is pumping fuel from the tank, into the pump, up to the filter, and back through the return lines. Since the injection pump is disconnected, it won't get any air in it and get air-locked.

    Only crank the motor for no more than 30 seconds. I have personally burned up a starter by cranking too long. Let the starter cool for 2 minutes before cranking again.

    When you see clean diesel fuel coming out the hose at the top of the fuel filter, shut the air bleed valve off, disconnect the clear hose, reconnect the pink wire to the injection pump, reconnect the glow plugs, and start it up. I guarantee it start up on the first try with this technique (as long as the injection lines didn't have air in them to start with).

    I know this seems like a lot of steps, but you should be able to get this all done in under 2 hours. I can do it now in under one hour. Using these steps makes it very easy to change the pump and bleed the fuel system.

    BTW...you can use these same steps to change the fuel filter. Just skip the part about changing the pump!

    Good luck!

    NOTE: Since the 82-83 trucks use spin-on fuel filters with no air-bleed valves, the only way to bleed the system is to fill the filters up with clean diesel fuel, install them, and then crank the engine over for a while with the pink wire disconnected from the injection pump. It's hard to know when the air is purged, but I have found that two 30 second cranking sessions should be plenty. Then reconnect the pink wire, and start the engine. Keep the motor revved up a bit until it seems to be running smoothly
     
  2. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    Excellent Casey!!! This one is a keeper for sure. I'll make it sticky!/forums/images/graemlins/thumb.gif

    Rene
     
  3. 6.2Blazer

    6.2Blazer 1/2 ton status

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    Wow, what timing! I was just going to get a new pump today after work because of a hard start issue.

    Regarding getting air in the injection lines, is there a way to bleed this, or should any air eventually be forced out once the engine is running??
     
  4. arveetek

    arveetek 1/2 ton status

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    If the engine will start and run, all air will eventually be bled from the lines. If you can't get the engine to start, disconnect the injection lines from the injectors, and crank the engine over with the pink wire hooked up to the IP. Once fuel starts dribbling out of the end of the lines, reconnect the lines and it should fire up. Remember to allow the starter some cool down time. If you think there is a lot of air in the system, remove the glow plugs to release compression to ease the strain on the starter.

    Casey
     
  5. Judd

    Judd 1/2 ton status

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    One more way of bleeding the air. As arveetek said, crack open the fuel line at the furtherest end from the pump. Then disconnect the glow plugs so they don't "glow". You will have the air cleaner assy. off anyway so just spray a small amount of starting fluid in the intake. Disclaimer here. ONLY A SMALL AMOUNT IS NEEDED! Like a one second spray-just enough to start it.
    Then if you want, you can keep it running a couple of different ways. WD40 lightly sprayed into the intake does the job well-once again, don't get carried away. The second way is a rag soaked in gas. There are plenty of dangers associated with holding a rag soaked in gas right next to a open intake so do this on your own accord! I can say that this is the way I bleed my 6.2 and it works well. I've done it this way for about 10 years {about 10 times or so as I usually change out the filters once a year. Plus things like fuel pumps and changing intakes}. Also, the friend who I picked this up from has done it like this for a long time with no incidents. Be carefull though! Wouldn't be fun holding a flamming gas rag, nor would the engine like a gas rag sucked ito the intake!

    I just sorta included this as a option if you really have alot of air in the lines. Like if you change the pump or run it out of fuel like I did once {broken gage}.
    If you have only changed the filters, it ain't that bad useing the crank method. And Murphy ain't as likely to pay you a visit either! One last disclaimer- Be afraid, be very afraid!
     
  6. edeslaur1

    edeslaur1 1/2 ton status

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    Uh, starting fluid (aka Ether) and glow plugs = bad things (like broken parts due to early detonation)

    Use WD40 if you have to use anything.
     
  7. Judd

    Judd 1/2 ton status

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    Uh,,,thats why I said to disconnect them! Read the post again feller.
     
  8. edeslaur1

    edeslaur1 1/2 ton status

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    Well, at least now the ether thing is out in the open where no one can miss it. /forums/images/graemlins/thumb.gif

    Here's how I started mine after an air leak at the primary caused me to airlock it. This way, I didn't need to mess with the glows or munching my battery.

    1) Make sure truck is either level or front end is pointing downhill!!!! If nothing else, whip out your hi-lift and point the a** end up. /forums/images/graemlins/thumb.gif
    2) modify extra gas cap to take an air nozzle /forums/images/graemlins/cool.gif
    3) set compressor to 8psi (OK, it was 12) and have helper hold nozzle and add air as I request it. 60 gallon tank takes a long time to pressurize at 8psi, so shouldn't blow any seals. Take it real easy anyways. (air on, air off, air on, air off)
    4) spin open primary filter enough to let air out and allow to fill using pressurized fuel tank. When full and running out, then snug down until no more leak.
    5) remove secondary filter and route extra line from tubing into can to collect extra diesel until no more air
    6) fill secondary and install
    7) disconnect fuel return line at injector pump & crank engine until no more bubbles (keeping pressurized may be optional here, but I left it at 8psi)
    8) crack at leat 4 injectors and crank until fuel drips out
    9) tighten them down and crank/pause until she starts (like 4 times)
    10) SLOWLY let the air pressure out of the tank. Sometimes the fillers go below diesel level and fuel, instead of air, will be coming back up at you. (e.g. Don't try this with your shop vac's exhaust. DAMHIKT)

    Of course, this only works if you have an air source and a buddy. You could mod the cap to take a valve stem and do it solo, but I would opt for 8psi then to be safe. Would suck to split your fuel tank at the seams (unlikely, but...).

    HTH! /forums/images/graemlins/k5.gif
     
  9. Judd

    Judd 1/2 ton status

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    I like your compressed air idea. I might have to snatch up a old gas cap and give it a try one day. Thanks feller, sounds like a good idea. /forums/images/graemlins/thumb.gif

    Hmmm, might try to figure out how to put a schrader valve on the cap. Then you could just put a locking type tire hose on it. Hmmmmm?
     
  10. doctor4x4

    doctor4x4 1/2 ton status

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    Thanks Casey
    I plan on doing mine tomorrow
    I have a a electric inline pump for emergency back up so bleeding it should be easyer
    but the damn turbo is gonna be fun to sneak the pump out from under
    Randy
     
  11. arveetek

    arveetek 1/2 ton status

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    You're welcome!

    However, when I installed my turbo, I elminated my mechanical pump completely and am now just using an electric pump for all my fuel supply. That turbo is just too close to the pump, and I knew it would be a pain to replace later on in the future. You could do the same if you wanted to.

    Casey
     
  12. doctor4x4

    doctor4x4 1/2 ton status

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    Hey Casey
    I agree 100 % did exactly the same now onto propane injection /forums/images/graemlins/thumb.gif
    R
     
  13. uglytruk

    uglytruk 1/2 ton status

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    ...and which pump brand to use... Cheapie AutoZap? Napa? Orginal Delco?
     
  14. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    Try www.accuratediesel.com

    You may have to talk to Tim through email or phone though. Last I looked I couldn't find 6.2 IP's listed anywhere...but I'm pretty sure he still rebuilds them and when I had mine done the price was damn good. Less than $350 including shipping and the turn around time was under 10 days.

    Rene
     
  15. uglytruk

    uglytruk 1/2 ton status

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    How do you know when you're inj. pump needs TLC? And Injectors? My 6.2 has 175K, I guess, and never smokes, except on real cold start-ups. But both exausts "puff" like one cylinder on each bank has a bad valve. I'm not sure if Diesels suffer burned valves like gassers. And BOTH pipes do it. And there's no crossover. Two bad injectors? Otherwise it runs pretty smooth. Just a light "chuff- chuff" And I'm quite familiar with a gas 305 having a bad spark plug. The engine chugs, this 6.2 has smooth power. Well, no 6.2 has "power", but you know what I mean!
     
  16. uglytruk

    uglytruk 1/2 ton status

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    Oh yeah, what about lift pump? Which brand...???
     
  17. 6.2K5Blazer

    6.2K5Blazer Registered Member

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    Is there a block off plate you can get to cover the lift pump? I plan on doing a turbo install here soon and would like to do away with the lift pump as well.
     
  18. Rob 85K5

    Rob 85K5 1/2 ton status GMOTM Winner

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    Reconnect the hard line before bolting the pump up. It makes it easier to line it up with the pump when it is not connected.
     
  19. lak2004

    lak2004 1/2 ton status

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    Just wanted to let everyone know that on my truck the lift pump bolts were 7/16" and the rod cover bolts were 10mm (best fit).
     
  20. AJMBLAZER

    AJMBLAZER Better to be lucky than good. Premium Member

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    What he said. I bet GM changed them over the years.

    Other than that my lift pump swap went great thanks to this write up. Swapped the filter and did it per this write up as well and viola, SHE RUNS!

    Doesn't seem to leak either.:thumb:
     

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