My truck has been having issues with the fuel system for awhile now. When it gets below 1/4 tank it always has to be primed before you can start it and it just runs real bad. Above 1/4 and no problems. No lift pump or anything. Everything is stock. Just changed the fuel filter a month ago and it didn't change anything except now when I'm on E and coming up to a gas station the truck will cut out. I'll have to get out and prime the truck to either get to the pump or prime it to restart it when I leave. Beginning to get real annoying. The filter head has been rebuilt recently too. I'm beginning to think it might be a pickup problem in the tank considering it only seems to happen when its below a 1/4. Anyone have an idea where to start? I'm lost.
Replacing the fuel head is something I might end up doing soon. I just have a hard time seeing how a cracked fuel head would give me the 1/4 tank issue. I would think that would be constant regardless of fuel level.
When the fuel is low in the fuel tank, the CP3 has to work harder in drawing the fuel, so the extra vacuum will find any leak [leaky seal or porous fuel hose] and allow air in the system. There is no factory fuel pump on a stock Duramax.
We also ran into this on our 7.3 Powerstroke. I don't know if it is an issue on these trucks, but when low on fuel, fuel sloshing would cause the pickup to suck air for a bit. There was also an issue with the fuel pickup foot breaking off in the tank, causing it to draw nothing but air below 1/4 tank. That was fun to find out there hard way!
In general it is best to treat any newer vehicle as if 1/4 tank is empty for a number of reasons.
The deteriorating fuel sending unit assembly in the tank, and/or the seal for it, has known issues of cracks/leaks that show up when the tank level is low. Sometimes even throwing a fuel limp code under heavy tow loads when below 1/2 tank.
They're not that expensive, just the hassle involved with dropping the tank.
This was something I was thinking about looking into. It makes sense that that could be an issue. Also the lines going to the CP3 very well could be weak since I'm at 220,00 miles. Where would I get replacements for those lines? I've heard the dealer is an expensive option when sourcing those lines.
A good quality 1/2" bio fuel rated bulk hose, with a strong vacuum rating. I use the blue Aeroquip here, which some site Vendors sell, or you can look locally, Napa sells some too.
These seals on the quick-connect flex lines can also be a leak source. This is the one attached to the sending unit. Tight bends in these can also be a collapse point.
I'll definitely be looking into that hose to replace mine. Also something I had forgotten to mention until it happened to me this morning. When I have to prime the system, after a few pumps the primer is nice and firm and you'll hear a hissing sound coming from right around the CP3. What hose/connection down there could be bleeding out the fuel? Another thing is that the truck will have great power on some accelerations but 5 minutes later it will still get up and go but it will feel laggy. Could this be related to my fuel issues?
Thanks
So drove the truck tonight for the first time in a few days. Its been sitting below a 1/4 and it had lost prime completely. Quick few pumps and back running. Decided to plug up my cheap scan tool and just take a look. The tool does give me the fuel rail pressure and what I found was strange. Idling below a 1/4 the pressures are all over the place. Anywhere between 4000-6500 psi. Never holds a fairly consistent reading. Below 1/4 full throttle never goes about 18,000 psi. Truck seemed to be running kinda laggy so I went and put 20 bucks of fuel in. After that the pressures idling stayed right around 4800 psi and only fluctuated by a slight amount. Full throttle I hit about 23,500 psi and held. That seems more reasonable to me. Anyone know what might be causing the low rail pressure when below a 1/4 tank?
So wanted to bump this but also have some new information. I was doing some more research and someone with the same sort of problem had someone suggest that if the fuel sending unit had ever been removed that it may have not been re-installed correctly or damaged in the install. Well the sending unit has been out once at the dealer after my dad stupidly filled the truck up with gas. Thinking back about it the truck never once had the 1/4 tank problem before the dealer worked on it. Once we got it back it has been constant. This was probably 3 years ago so taking it back and complaining isn't gonna work at this point unfortunately. I could easily see a tech being careless if he wasn't having a good day or something like that and accidentally damaging the sending unit. I still think the fuel head could be a contributing factor but I have gone over it and not been able to see any sort of crack and the head has been dry for weeks. My plan now is to pull the sending unit and look it over for any cracks/holes. It just seems like the most logical place to start now that I have kind of a start point of the issue. Anyone else have any other recommendations?
....My plan now is to pull the sending unit and look it over for any cracks/holes. It just seems like the most logical place to start now that I have kind of a start point of the issue. Anyone else have any other recommendations?
A few items from the plumbing dept with an added gauge for testing, let's you apply 3-5psi at the tank fill and help find any leaks forward to the filter head.
I wish I had the money to add a lift pump but just don't. Also I just dont see how the filter head is causing the loss of prime only at lower fuel levels. It pretty much happens within a few seconds of cutting the truck off at low fuel and never when above a 1/4.
Its been awhile since I've updated this. Never got around to really working on fixing this with school going on and all but finally started yesterday. Pressure tested the fuel system and found no leaks whatsoever. Atleast thats what I thought until I saw fuel dripping down the back of the motor. Look down and where the rubber line goes into the CP3 by the FPR was covered in diesel. Figured check the hose clamp first. It was loose as could be. Tightened it up and no more leak there. Still loosing prime overnight. Remember this only happens overnight at 1/4 tank or lower. Pressure test today and figure why not spray down the filter head and lines with soap and water. Still nothing showing up. The WIF sensor occasionally has a drip or 2 and if I leave the truck sitting a week or so even with a full tank it will lose prime. I'm planning on swapping over to a nicktane adapter or making a DIY filter and lift pump setup so the WIF sensor wont be around much longer. Would that sensor cause a quick loss of prime at or under a 1/4 tank? I'm starting to lean towards the pickup in the tank having an issue since im not seeing any external leaks.
So WIF leaking would cause a loss of prime overnight or over a few days but not just at a certain fuel level or almost immediately once cut off at certain fuel levels?
WIF leaking after shut down will cause prime loss, regardless of the tank level. And it's such a small amount that drops straight thru, it can go unnoticed for a while as there's no residue on anything below it.
Losing prime in the system can source from various areas. For most, it's the filter head (WIF included) and/or those two lines to/fro the filter head, but as tank levels drop low, other areas can be suspect too, as it's harder to hold a vacuum than it is when the tank is full.
Fix the problem you have 1st before adding stuff; filter head adapter, lift pump, etc.,....otherwise you can just create more problems as it masks the original problems.
So changing the WIF sensor or swapping to the CAT filter is definitely in the near future for me. Also, when it drops below a 1/4 the truck loves to lope at idle and just run like crap all around. I'm guessing whatever leak I have is causing that too? I guess the WIF sensor could suck in enough air to cause that but it doesn't seem like it would cause it to lope.
I know a leaking fuel filter head can also cause a lope at idle. Perhaps the WIF leaking also can?
Rebuilding isn't always successful. A new filter head assembly comes with a new WIF and a fresh filter and eliminates many potential leak areas, including a possible crack in the filter head itself. It'd suck to replace the sensor that you know is leaking, and later find out the filter head was also. Downerrr
$100 for an adapter, so you can run a lesser filter with no water protection.
Not a good idea. Fix the leak you have before potentially adding to the problem.
Update from today. Installed clear tubing in place of the lines to and from the filter head. Once primed up the line from the FICM is solid with fuel but every 30 seconds or so it will pull air bubbles through then after about 30 seconds it will get back to solid fuel. The line off the filter to the cp3 is constantly full of air bubbles and isnt always full of fuel. All this was done below 1/4 tank. When cut off the fuel stays in the hoses and doesnt seem to bleed back but when you try to restart it cranks over for 10 seconds or so before it finally starts. Also with my luck the injector return line that comes to the test port block underneath were the line from the filter is starts pissing fuel everywhere and its cracked. I've got a return line kit ordered so hopefully that fixes that. I removed the filter head and all also to look for cracks. I found what looks and feels to be a crack in the aluminum. Its running down the bracket where it connects to the motor and halfway to the edge of the head. Pressure testing the head with one side blocked and 5 psi didnt show any leaks however. Sprayed down with dawn and water and no bubbles or anything. Money is kinda tight at the moment so being that its not even leaking I have trouble coughing up the money when its not reacting like its cracked. Something that just occurred to me now. If the suction side of the cp3 is getting weak could that just be my whole issue? Tank level gets low enough and it just cant suck hard enough and has no air leaks? Just a thought I had.
Also does anyone know what size the injector return line hose is? I know its not the right way to do it but I wanna temporarily replace the line while the actual kit is in the mail so I can keep working on the truck and testing stuff. Its the one that comes off number 1 injector and goes to the test port.
While I'm on the subject of injectors, number 5 and 7 are at -5.5 and 5.8 on the balance rates. Could that have anything to do with my problem with holding prime?
Filled it up just to get her over a 1/4 tank today and bam no air in the clear lines whatsoever. Starting up like champ. I think I'm just gonna pull the bed and check the sending unit just to rule it out. Stopped by the local dealer and talked to the duramax tech and he said that would be his first guess considering it only happens at that level. He said it wouldn't hurt to replace the entire filter head just because of age but he said it really wouldn't be possible that it is causing my problem even with the leaking WIF sensor.
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