Basranabread

Replacement pump arrived yesterday evening and I installed it immediatley and took the truck for a test drive. I'm happy to report it ran absolutely perfect and even at wide open throttle I could not notice the fuel pressure gauge dropping at all. Happy to finally have this solved and thanks everyone for your input and help!

I have finally had a diagnostic breakthrough this evening! I was preparing to run the truck out of some 5 gallon pails and in doing so I decided to use the lift pump to fill my pails. I removed the outlet line from my filter housing and ran it down to a pail. While running the pump like this it remained noisy and I observed an insufficient amount of fuel coming out. I still wanted to bypass my suction side components to rule out an air leak so continued to use this method to fill the pail enough to use for fuel feed. I then ran an about 24" line from this pail to the suction of the pump and left the discharge line in a second empty pail. I ran the pump for a minute and it only filled the pail a generous 1/4 full. It also remained noisy the entire time during this. The results of this tells me that the pump is faulty. During my test drives I would always follow the same route and drive the truck in the same manor during the drives. Each time I would experience my symptoms in generally the same location. My speculation is that the pump would generate some heat and cause either an oring or seal in the pump assembly to leak air or an already damaged pump to act up. I did also talk to an airdog rep yesterday and he mentioned that the regulator being loose initially could have prematurely damaged the pump and agreed to send me a replacement. I believe after my last test drive the damage to the pump became great enough to cause it to have these issues cold or hot. This would explain why it passed my previous bucket test. So I have a new pump on the way, I will bolt check it and swap them out. Once this is done I will report back either good news or bad but I am very hopeful this will resolve my issues.

So I gathered the appropriate fittings today and removed the quick connect fittings on the suction side tonight. I also rigged up the fuel gauge into the cab of the truck to monitor and took the truck for another test drive. Exact same results. Pressure remained steady on the gauge and all seemed well for the first little bit of getting heat into the truck. Once warm I did a full throttle pull and it actually seemed to act as it should. Pressure stayed steady and truck seemed to have good power. After about another 5 minutes I tried this again and pressure dropped off slowly with throttle application. I pulled over to see if it would recover and it did, very slowly. The needle on the gauge was jumping slightly indicating air ingress or churning and the pump became noisy once again. I shut the truck off and primed the pump a few times and it became quiet. I then started it and drove again, hard throttle acceleration and pressure drops off with a noisy pump. It got so bad on the way home that basically any amount of throttle application and the pressure would fall off slowly so I would pull over to let it recover. As I have gone through everything and mitigated any potential causes of air leaks on the suction side, I don't think I have anything else to blame besides a faulty o ring or something else with the pump.

Gotcha haha, at this point I am just throwing anything I can think of at this truck so maybe I'll swap the pins in the plug tomorrow just because

I also don't believe that the pump would create any fuel flow towards the engine if it was running backwards? It's an internal gear or gearotor pump. As far as I know if you spin them backwards you outlet and inlet ports are then reversed. I could be wrong on this though as the internal return may complicate this scenario. No luck on fittings for the in cab gauge or suction line today unfortunately. I will attempt again tomorrow and update if I can make anything happen.

You are correct and I had the exact same idea to rig up a gauge I can monitor on test drives, working on this today. Is it possible something is in the tank? I guess but I have had the fuel sending unit out twice during this process, shined a light in the tank to inspect while looking for restrictions. I even put my arm in the tank through the sending unit hole and swept around to see if I could feel anything as I could not see anything. My next step is I will attempt to replace the suction side quick connect fittings with hydraulic or whatever I can come up with today. I have a hydraulic hose shop at work so have a large access to fittings and adapters. The fact that the pump is still making cavitation noise after regaining pressure post losing it makes me suspect air ingress and with nothing obvious I'm hoping it is indeed these fittings.

Sorry @Tractorman, I mentioned in my response to mopar1973man that I had performed the tests prior to another test drive and all seemed well. I removed the discharge line from the filter housing and ran the pump. It produced approximately half of a 5 gallon pail in a minute which is about what it should do. I then took the truck for a test drive and the exact same thing happened. All was well until about 45min into the drive, I layed into it (low on power) then tried again with slight hesitation. Checked the pump gauge and it was 0psi again with a noisy pump. Pump again is now noisy and cavitating once again. I left the truck for the rest of the evening out of frustration but am going to perform this test again tomorrow with a now "angry" pump to see if the results are different.

Mine has the quick connect fittings. I just tested everything above and it was all good. Took the truck for a drive and was okay until I got into it hard again and did the same thing 0psi on the lift pump and hesitation like crazy. I have these push lock fittings at work so will attempt to replace them all and see what happens.

Okay so it's basically like 3 return circuits then. Pump returns internally to itself, vp44 return and injector return which share a line back to the tank. Learned something there. Since the pump internally returns, is it possible that this regulator being loose pulled in air and caused an airlock in the pump? Causing my noise / 0psi scenario and when I opened the fuel bowl drain it purged it which resulted in the pump sounding and acting as it should now?

As far as I am aware it uses the return line off of the vp44 which heads to the firewall and T's together with the injector return line and back to the top of the tank. It has a ball check pressure hold back in the banjo bolt that connects this line to the vp44.

This lift pump uses the factory return line to the tank and is a frame mounted pump. I agree completely that it is was fuel starvation and am starting to think that it was cause by the loose pressure regulator. I am going to perform this test today and report back. I suspected the same as you are saying here. I did remove the box from my truck and go over everything from inside the tank to the suction of the pump and found no blockages or large airleaks. The only time it read 0 psi was prior to me discovering the regulator assembly was loose from the pump (assembly error from airdog) and leaking fuel out. The pump has been intermittently noisy ever since this discovery until I cracked the drain on the fuel bowl during diagnosis. Which puzzles me.

@Great work! Thanks for that, to save people from reading back in the thread I will ad that I installed an airdog raptor 150gph kit in the truck. That included 1/2" fuel line upgrade aswell as a 1/2" draw straw upgrade so everything from draw straw to the filter housing is brand new. I also pulled my box on my truck and went through it all after this incident and found no issues, airleaks, or blockages.

Awesome amount of information in the previous posts, thank you @W-Tand @Tractorman, I really appreciate it and also supplied the answers I was looking for. @TractormanI did end up purchasing the 150gph pump. I do realize it is overkill for my current application but do not plan to keep the truck stock forever and saw no harm with putting an "overkill" pump in it right now. I also went with the 2 year warranty DAP vp44 and red head steering gear. Now this brings me to my next issue that has me scratching my head. I finished the install of all of this the night before last. All went well, truck primed and fired up as it should. On my maiden voyage after about an hour of normal driving I decided to get on the loud pedal a bit. When I did I thought to myself "seems down on power up high" so I now curiously continued driving normally. Shortly after I got into it again and noticed the truck hiccup like it was starving for fuel. Got off of it immediatley and then rolled back into throttle very lightly. The truck hiccuped again and continued to do so anything over 1/4 throttle. I pulled over and jumped out to look at the gauge installed on the Raptor lift pump. 0psi is what it read! I turned the truck off immediatley and checked the fuse to the pump. All was good, I bumped the starter to run the pump and the pump ran but very loud (sounded like cavitation) and gauge stayed at 0psi. I repeated this three or four times until the pump finally decided to build pressure once again but remained noisy. I then limped the truck home to inspect further and when I did I noticed fuel dripping off of the pump. The 4 bolts holding the pressure regulator on the side of the pump were finger loose and fuel was coming out around the regulator. I tightened these and it appeared to seal up. I then started the truck and the pump remained noisy but was reading pressure on the gauge. I then shut the truck off and bumped the key to run the pump and it continued to sound like it was cavitating but there was pressure on the gauge. I ended up pulling everything apart pre pump to check for air leaks or restriction to no avail. I then fired the pump several times in a row and about the 4th time it became quiet sounding like it should. Then primed it a couple more times and it started cavitating again. While it was cavitating this time I opened the fuel bowl drain. It pushed fuel out no problem and after closing it the pump has been quiet. I have contacted airdog about this and they would like a video of the noise the pump is making. I cannot get it to do it again since I cracked the fuel bowl and I'm not convinced it is solved since it was doing it intermittently. I am now paranoid to drive the truck and potentially hurt my brand new vp44. Could it be possible that the leaking regulator allowed an airlock into the system and me cracking the fuel bowl drain purged it? Could the loose regulator also have caused my initial pressure loss aswell? My brain is melting trying to make sense of the complete loss of pressure paired now with an intermittent cavitation sound from the pump that I cannot replicate after simply opening my fuel bowl drain during diagnosis 🤯. Any input would be greatly appreciated!

My feeling is that if I'm seeing the light come on at 10psi, I'm already below the recommended supply pressure of 13psi on DAP's website. I can see that and identify what the issue is, whether it be the pump getting weak or something else. With a 150Gph pump, and the truck otherwise stock, I don't really see the need to monitor a gauge constantly. My reasoning is If the light ever turns on I'll just know to replace the lift pump before damage is done.

Hey guys, Sorry for leaving this dead in the water for so long. Sold my shop property which caused the truck to be tucked away and ignored until now. I did the hotwire test and the pump is confirmed dead. So now I have some questions about injection pump options. I took a look at DAP and they seem like a strong option. The only other one I am considering would be a Blue Chip. When comparing the premium upgraded vp44 from Blue Chip to the 2 year warranty version from DAP the only difference I can see that is apparent from the descriptions is that the Blue Chip version has a steel sleeve in the housing where DAP is aluminum? It seems there isn't much else that differs in the pumps. Both use new electronics and both have Bosch upgrades / updates to the internals. Does this justify the $1000 price increase for the Blue Chip? I'm also going to pair this with an AirDog Raptor 150Gph lift pump, is there a fuel pressure indicator light set up that isn't 5psi? I'd be much more comfortable with the light coming on around 10psi but can't seem to find anyone that makes this. I'm not a big fan of mounting a gauge in my truck, I like the clean, OEM as possible, look so an inconspicuous indicator light would be best for me. Also plan on throwing a steering box in the truck, was planning on doing a redhead unit but since I'm already asking for your input I figured I would see if anyone has a different opinion or better option on that as well.