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Discussion Starter · #1 ·
So replaced the fuel filter for the first time on my 2016, went to prime the pump by opening the bleeder screw and kept pumping but never got any fuel to come out the bleeders screw. Tried what some suggested by closing screw and pumping a few times and opening the screw, and repeating, still couldn't get fuel to come out screw. So I took off the filter to see if the gasket was out of place but it was in place. But I did notice that inside the fuel filter it had fuel in it, looked to be about the same amount of fuel as the old filter when I took it off. So I put it back on and tried pumping with the bleeder screw open and could not get fuel to bubble out. So I went ahead and started the truck and let it run for about 10 minutes, and then I put the fender lining back on while still running the engine, so that means the engine ran continuously for about 20-25 minutes no problems. I am assuming that was more then long enough for it to run beyond then the fuel that was already in the system. So what I am asking is was I suppose to see fuel squirt out the screw? There was fuel in the new filter when I took it off to checked the gasket. Should I not worry since I let it run 25 minutes no issues. Thanks for any guidance. This is my first diesel engine
 

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You are likely OK but it should bubble out the bleed screw, I would maybe run some laps close to home and then not worry maybe a fluke. I know they are hard as hell to get to screw and primer pump on a LML so maybe it just wanted a more vigorous pump. Sorry could not give a definitive answer but if its running and starting OK you should be fine.
 
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Honestly, do yourself a huge favor and install a lift pump.... preferably one with extra filtration such as a FASS or AirDog.

I've installed a FASS and when I change a filter (either the FASS one or the OE one), I prime it by pressing a momentary contact micro switch I installed under the truck near the FASS.

My FASS is mounted above the drive shaft just fore of the rear diff and the microswitch is mounted inside a sealed plastic box. When I want to prime the system I just flip the lid off the little plastic box and press the microswitch with one finger/hand and have the other hand on the FASS filter to tighten it up before too much fuel escapes. With the OE filter, which doesn't get changed very often because the fuel it gets to "see" is already as clean as a whistle, I do the same but have to just monitor the fuel escaping from the bleeder screw from where I'm laying on the ground near the back wheel.

Roachie
 

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Thanks for the reply. This my first diesel, can you tell me what the advantages of adding a lift pump are. Thanks
GM don't supply a pump in or near the fuel tank to send fuel up to the engine compartment.

Instead, they rely on the High Pressure Injection Pump (HPIP) to create a vacuum in the fuel lines including the filter to "suck" the fuel up from the tank.

Try to imagine for a moment....you are up in the engine bay with a length of tubing going all the way to the back of the truck and into a soda bottle....but in between the tubing goes through a restrictive canister (ie: the fuel filter).

Now try to imagine sucking that soda drink through the tubing. You might be able to do it, but it's not going to be easy.

Add to that the fact that there are several junctions between rubber hose and steel tubing and the IN/OUT from the filter housing.....all of which are potential failure points....if one of these joints develops a tiny air leak, then you're going to be sucking AIR, not soda (or diesel fuel in the case of your HPIP.

Add to that, the CP4 HPIP in the LML is reputably an inferior product to that which was provided in the earlier models; which had a CP3 HPIP.

The CP4 needs all the help it can get to avoid self-destructing.

One of the best things you can do to try and protect your vulnerable CP4 is to take away one of its tasks....by adding a good quality lift pump which will ensure it ALWAYS has a good fuel supply to its front door.

I've gone one step further in my quest. I've added a Beans Diesel sump kit.


The reason for this bit of gear is this: The lift pump draws fuel from the tank at a much faster rate than the HPIP did on its own. The FASS takes 150 gallons per hour and returns most of it back to the tank.

Have a look at this LONG video for the reasons they do this....


That's all good and well...but the portion of the fuel "system" between the bottom of the tank and the inlet of the FASS (or any other lift pump), relies upon the "drawstraw" that lives inside the tank. That drawstraw is the next weakest link. There is a phenomenon known as "the quarter tank issue".

This relates to the scene inside the tank. The drawstraw goes from the top of the tank to the bottom of the tank, where it resides happily inside a plastic canister called a "swirl pot". The height of this swirl pot is approximately 1/4 the total height of the tank. While there is plenty of fuel in the tank such that the fuel simply falls into the swirl pot, all is okay.

However, when the fuel level in the tank gets to a point where it is below the lip of the swirl pot, the fuel has to enter the swirl pot via a relatively restrictive small hole. The result is that the FASS itself can cavitate and starve for fuel....which puts you right back where you started; no fuel getting to the HPIP.

I hope this explains it reasonably well for you.

Cheers from Australia

Roachie
 

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How far open are you turning the bleed screw?

They just need to be cracked a tiny amount - enough to let air/fuel blow thru.

I've never had the type of trouble being described when priming any of my dmax's.


It may need repair/replacement of the primer.
Some have had to replace fuel filter heads.


There is way the GM service and dealer system would put up with that kind of trouble if all of those engines had that kind of trouble priming.

And for that matter, there would be many threads about it on every diesel forum if they all had the problem.
Sorry, but it sounds like a 'method' problem or a 'broken part' problem.
 

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Discussion Starter · #10 ·
I tried cracking it, I tried a couple turns open. I just got done driving it a bunch and no issues. So I just tried cracking the screw, thought I heard air release, tried priming and nothing. Closed screw and drove some more. Must be the priming pump. Weird thing is that when I first installed and it didn't prime and I took the filter off to check seal, there was fuel in the filter similar to when I took old one off. Even though the truck seems to be getting fuel, I am going to take to dealer, hopefully they won't say I broke it!
 

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Update - So I went to a Chevy dealer today to talk with a service writer to see if I needed to have the fuel prime looked at, and all I can say is that I am stunned at what happened.

I go in there and tell him that when I open the bleeder screw and pump I cannot get any fuel to come out, but that I was able to start the truck and it is running but the primer pump is not doing what it says it is suppose to do. He tells me I am doing it wrong and that I should only press the primer pump with the screw closed and that you only open the screw if you are going to turn the ignition over to and let the system pump fuel out the screw and this is how we do it. I said that is not what it says. He says where did I see that, an I say the online Chevy manual, he then says that is my problem and what do you want from me, I need to take care of customers and walks out his office. I guess I am not a customer.

I go to my truck and pull out the manual, go to the page that tell you how to prime, walk back in there, hold the manual up and he says I don't have time for this and to leave. Both encounters didn't last 5 minutes total so this guy thoroughly dismissing me and won't listen.

I am fuming at this point walk into the service managers office and calmly tell him that one of his guys has a problem and what my problem is with my truck. He also tells me I am not priming right. I show him the manual and says I am right that manual does say crack the screw and pump til fuel comes out but that they just put new fuel filter on and pump with screw closed and start truck.

Am I missing something here they had me thinking I was doing it wrong? I guess I need to go to dealer I bought from, they are just farther away.
 

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Yes, find another dealer..
 

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From ALLDATADIY:


  1. Prior to priming the fuel system, ensure that the following has been completed:

    • There is fuel in the fuel tank.
    • The fuel filter has been installed and properly tightened.
    • The fuel lines are properly connected.
    • The fuel filter is cool to the touch.
    • Any dirt or debris has been removed from the fuel filter adapter and vent valve screw.

  1. Remove the air cleaner outlet duct.
  2. Open the vent valve screw (1) by turning the screw counterclockwise several full turns.






  1. Operate the priming pump (1) until a small amount of fuel seeps from the vent valve. Allow the pump to fully return upward between pumps. When fuel is present, the filter is full of fuel and the system is primed.
  2. Close the vent valve screw.
  3. Clean any fuel which accumulated on the fuel filter adapter.
  4. Install the air cleaner outlet duct.
  5. Start the engine and allow the engine to idle for a few minutes.
  6. Check the fuel system for leaks.
 
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Thar's pretty much exactly what the 2011 (LML) diesel supplement to the owners manual says as well.
 
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