New AirDog losing Fuel Pressure, Out of ideas

[BrianO]

2001 Ram 2500 w 5.9 HO, 6-Speed, external fuel pump - Stock - I had 2-3 times where I had the Dead Pedal issue, so while tinkering I decided to give it more power for towing so here is what I did

• AirDog 150, pulled bed, installed draw straw 1/2 inch from the bottom of the tank, Ran outlet right into VP44. - Removed old filter and pump off the side of the engine and capped.
• Cold Air Intake
• Pulled Turbo Silencer Ring
• Gauges, Oil Temp, Oil Pressure, Coolant Temp, Boost, EGT and Fuel Pressure, Fuel pressure sender is mounted on the Air Dog port, did not use snubber
• Edge Comp for Tuning
• 5" Turbo back straight exhaust

Bled everything and got it fired up, Holy Crap - Sweet! Took it out and found a problem. Fuel Pressure at startup is about 14psi, driving, WOT it would drop 2-3psi then climb back up at idle, exactly what I expected. 

2 min into the drive, pressure dives down to about 5psi, WOT down to 0-1psi, WTF, pull over, turn off, restart, back to normal, runs 20 min til back home, thought Air bubble or something like that.

Next Day, same thing normal then pressure dives, once down, pressure does not recover unless I sit with the vehicle off for some time then restart, will not go back up on its own.

First Thought was gauge - ran a T off the airdog, then added a Mechanical Guage in, readings exactly same as the electronic one, so it's not the gauge.

Next Looked at voltage - Solid 13.5v to airdog. Slowly pinched offline to VP44 and pressure climbed as anticipated. For a short term fix, I added two small washers to the AirDog pressure spring and ball, essentially stiffening up the spring, Now pump pushing 20psi at start and then when it drops it goes down to 9-10psi, so at least I am not going to burn up the VP44.

Had a long talk with AirDog Support, Now things get weird. Pull the washers, test - 15psi startup, 4-5 when it drops. Now I hotwire the pump to an external 12v battery, and pump spins up, Check Mech Gauge - pushing 15psi, engine off, and it stays at 15 for 15-20min. Now I start it up, and holy crap, 3 min later... DROP, down to 4 psi. Now that I can hear the pump once I turn the engine off. I can hear it is making a distinctly different noise, a higher pitched whine to it. The pump stays that way until I shut it down and wait 30 seconds to a minute, fire pump, 15psi, pitch lower and sounding like its pushing solid fuel. Talk to AirDog, since we were on an external battery not tied to the truck in any way, They agree to send me a new pump out. 

Get a new pump, install pump, fire up... the same thing happening, so it's not the pump. Now really getting frustrated. Start thinking it thru, Maybe it's the return to tank valve, should open up at about 14psi, order valve, replace it, Toss in a new Timbo APPS while I am in there and calibrate it. Fire it up.. No Change - same symptoms.

I am now plum out of ideas, Not getting any codes thrown, truck runs like mad, even at low PSI, not a ton of smoke at any setting but great power. But..... I just don't know.....

Just to clarify, the pressure does not creep down and settle at 4psi, and it literally drops as if someone flipped a switch and the sound on the pump changes to the higher pitch. It stays there until I turn it off and restart, I can put the clutch in and kill it and coast for 30 seconds then restart, and this fixes it about 60% of the time.

Begging for someone smarter than me to help as I am plumb out of ideas, all I know is I can't take my grandkids out camping like this

Thank you in advance - Brian

[Me78569]

Edit: just saw that you said you pickup was 1/2" off bottom.  I am betting that is your issue if you have anything other than a full tank of fuel.  My draw straw sits maybe 1/8" off bottom or less.

 

 

I fought this issue for many years and many replacement pumps. The only thing that solved it was a different pump.

 

 

I threw in big line kits, replaced, this and that, tested for leaks etc, with no success. I pulled the air dog out and put a pure flow(original owners new company) in and bam no more issues.

 

 

For good measure I would pull the tank pickup and verify it is all good. Ensure you have a full tank of fuel. 

 

 

But the different noise you head is kinda key to pump issues.

Edited October 29, 2016 by Me78569

[JAG1]

Sounds like the tank vent might be clogged. After a run open the fuel cap very slow and listen for air sucking in. Or run without the fuel cap. Also make sure your drawstraw isn't sitting too close to the bottom of the tank.

[01cummins4ever]

I would lean toward a suction issue, the pump making high pitch sound is probably cavitating, sucking air. 

 

[Mopar1973Man]

I've got only the thickness of a quarter (coin) from the tip to the tank. So I'm going to have to agree with above post it's most likely cavitation issue and you are going to have to replace your draw straw.

[JAG1]

7 hours ago, Mopar1973Man said:

I've got only the thickness of a quarter (coin) from the tip to the tank. So I'm going to have to agree with above post it's most likely cavitation issue and you are going to have to replace your draw straw.

Your draw straw is cut at an angle on the tip too, if I remember correctly.

[Mopar1973Man]

No. Flat... Just lightly notched. All I did was lay quarter (coin) on the tank bottom measured to that and cut the straw flat. Then with an angle grinder lightly notched the tip no more than a 1/16" deep on the notches. No its not touching the bottom. Also for every gallon of diesel fuel is 6.1 pounds so by the time I get a full tank bottom deflects away from the tip of the straw another 1/8 or so.

 

That's your problem now your straw is 1/2" away and as you fill the tank the straw is actually farther away from the tank bottom so air issues can become worse.

Edited October 30, 2016 by Mopar1973Man

[JAG1]

Mines doing the same whistle on low tanks. Real bad when I slosh fuel to one end of the tank or the other. Even happens sometimes at half a tank if I slam the go pedal off the stop sign creating a negative vacuum in the tank draw straw and make l/p work harder.

 

I'm going with a fuel tank sump and brush guard and let gravity help flow.