Duramax LB7 Losing Prime when parked? Heres how to fix. Silverado 3500HD

welcome back to the spank ranch garage i have a 01 lb7

duramax

it's leaking

prime

fuel

when

the truck stalls it's been getting worse like it used to be you know it's two days it cranks a little more now it sits an hour and cranks a little more so let's get into troubleshooting and fixing this issue, so we have our HP tuners hooked up here, we're going to use this for our data by logging this line right here, actual fuel pressure and desired fuel pressure, so no i started the truck but it's cold it's been sitting all night we want 430 uh bar which is about 6200 PSI right now it's about 10 bar it's probably not even real so let's give this a spin and see if we can get the fuel pressure right, now I look like a big hole because it started totally fine, so what do we learn here?

It started fine and then it died, which means we had a jet of fuel leading to the injection pump, but we had air following it and now it's off, so I think if I restart this we'll see that we have no fuel pressure, so as expected there is no more fuel pressure available under the hood here behind the charge pipe you have the filter head and you have a

prime

r on top of it you push this it's very smooth it shouldn't be right

when

this it's prepared, that thing should be pretty stiff in the back, you've got a fuel bleed screw, right here we're going to loosen this screw.

The gear comes out right there. I'll pump the primer a couple of times now that we have some fuel, so we're completely stuck in the air. That's good, that's good to know and that's good to try. The question is how does that register on the air, why did this happen and how do we fix it? So I removed the engine top cover and intake pipe so we can see what we're working with now. What I think is happening is I think somewhere between the CP3 high pressure injection pump and the rest of the truck I think I have a small air leak and if I had to guess it's after I turned the truck off because the engine is higher than the fuel tank, the fuel returns to the tank and we get a big gulp of air. here and then you know you're going to start the truck, you've got some fuel leaning against the injection pump, it stinks, that bottom arm kicks in and all of a sudden, oh, we're stuck, you've got to prime. and then everything works again.

The interesting thing is that although I don't have a fuel leak, we do have something that allows air in but doesn't allow fuel out, which makes troubleshooting a little more difficult, but I hope we can find at least a connection. wet or something that indicates that we may have a leak. My eyes are on the suspect here and it's very hard to see if you look down, that looks wet to me and that hose is facing inward. It's a pretty crappy shape and looking over the side I also see moisture on the outside of the hose next to the clamp.

I can't access any of this, but with the alternator off I will be able to. I've practically inspected everything. from the fuel tank all the way so the fuel comes from the fuel tank to these two hoses back here with these quick connects this run metal lines across the valley through a million piles of garbage to the ficum back through the fickham that's just for cooling, then it runs into the filter housing, this is the suction side of the filter housing primer trap and then it comes back out of the filter housing running to the front here and then to the CP3, finally now also on this there is a test port or yes test port purge port damn things there is this port for whatever you use this I don't actually use this port for anything.

I don't find it that useful. I don't have an adapter for it, but there is anyway. There is also a flexible rubber hose that needs to be inspected, so knowing that the whole truck looks good up to this point, I'm going to remove the belt, remove the alternator and think that we are. We're going to find our leak down there, we had to remove the AC compressor to turn off the alternator now that we're down here, I see that glow there, fuel residue, it's not enough to drip, there's fuel residue and then up here. We have the same story, there is fuel residue in that, so I think the best thing I can do is take this out, replace this piece of pipe and put new clamps on it.

It looks old. I changed a lot of this when I did the head gaskets. truck, but I didn't change everything, but overall this whole valley-like area seems to have some fuel residue. This was taken out. I haven't touched this clamp and I can twist this banjo connector on the hose, so while that's not good, it's a good sign that we may have our problem here. This hose is just broken, so I'm going to replace it. I'm surprised I passed this up because I remember replacing a lot of hoses on this one. engine, but that's how it works, the one you don't replace is the one that ends up burning you out, luckily this one is just, you know, a couple of pieces from the top of the engine to get to it, there's a couple of hoses in the valley, uh. on the back of the CP3 that if they leak you're going to have a really bad day, so let's see if I have any hoses in stock for this.

I have a new piece of hose here. The new crush washers on the fickham didn't have the clamps I wish they had, but I think these will do. First I want to clean the whole system with some brake cleaning so it's all dry in there and then I'm going to turn the key on and let the lift pump run. for 30 minutes or so and that will get this whole system up to four PSI or something like that on diesel and then we'll do a visual inspection for leaks again. I think this will be it, but if not, we will do it. dig deeper, okay, it's been running the lift pump for about 40 minutes, now you can see everything here is completely dry as expected, so no obvious leaks, not that we had an obvious one before putting the thing back together engine now. turn it on, make sure everything works well and then we will see if the problem has resolved itself.

The strange thing was that this purge was super soft. I mean, you'd push him, he just felt like a piece of trash now that this is all set up. The thing is rock solid, you can move it a little if you want, but you can't really move it much, so I think that's a good indication that we're holding Prime here, we're going to let the truck sit for a couple of hours . Let's make sure this is still hard and then let's give it a cold start, burn it into HP tuners and see how quickly it builds fuel pressure.

It's the morning, 12 hours later, the trucks are sitting with the front end higher in the back, which is the worst case scenario, so let's give this thing a spin and see how it goes, that's Everything guys, just a little piece of hose like this can park one of these trucks or give you a lot of headaches, um, this is very easy to fix one easy to find there will be times when it will be more complicated, but you I say that this fuel system has to be absolutely airtight. Probably one of the biggest problems with these trucks is that small air leaks can cause so many problems, so anyway, thanks. for seeing Grant's garage get hit, you have a problem with your truck, put it in the comments.

I will help you solve it. We'll talk to you next time. Quick fuel system function. Talk here. This is how the fuel system works on these early Duramaxes from fuel. tank you have your suction line it's a half inch line that comes out of the sending unit half inch rubber hose goes to the metal goes to the metal rubber hose goes to the metal uh back to the metal here now I have a lift pump indicated here these don't come stock, a lot of guys will put an air lift pump in here but it's not absolutely necessary anyway so behind the brake booster is where the final rubber hose goes into the metal hose with that quick connect that I showed you earlier in the video. that metal hose wraps around the valley of the engine to this little piece of hose right here, which is what we found to be leaking, that's what goes into the ficum, which is the one that uses fuel for cooling, so that the fuel simply passes through it. the other side goes to the filter head of the filter unit and then goes back to CP3 so you take another rubber hose back to CP3 and all for CP3 there is another rubber hose that goes back to a metal line as far as is this point.

That's where the brake booster goes back to the rubber and metal hoses all the way to the end of the truck, through the fuel cooler and back to the fuel tank, so you can see there are so many transitions between the metal and rubber hoses and it's kind of just a very complicated fuel system, especially for a truck that doesn't come with a lift pump mounted near the tank, so your CP3 creates that small amount of suction and it has to go through the filter, the ficum , all these lines, all the way back to the tank now, what happens is as soon as there is a gap, there is some way to introduce air into this system.

Nothing prevents this from being removed while the truck is off, so what you have here, the CP3, is actually mounted further down the valley. This is a little misleading, but the other elevations are correct. We discovered that our leak was right here, so it's likely that when we introduced air into this corner, we allowed it to drain back into the truck this way, but we also allowed the fuel to come through. It goes back down through the ficum in the filter and comes back because we broke that vacuum because we have that air leak, so this little slug here is where we have fuel leading to CP3 and we would pretty much be empty out the back of it. so just fixing that little leak all this stays primed now that i

parked

the truck for a couple of days it turns on no problem but anyway you could have leaks at any of these points they all give you more or less the same result but There are clues you can continue along the way to try to pinpoint exactly where your leak is, this is how it works