danalex

Ok, this is weird. Couple months ago I got a used 35-40gal in-bed aux fuel tank. I set it up for "gravity feed" using the kit from Northern Tools. Filled it up. After about 1/2 tank usage, my Quadzilla Commander started indicating low-fuel pressure..dropped to 2-3psi according to the Commander. I also had a quirky performance issue; after starting up, it would not accelarate beyond 25-30mph, for about 3-4 minutes of driving. Then all of a sudden it would drive and accelarate just fine (like normal) for all day long and the fuel pressure came up and steady (11-13psi). It did this 2-3 times. I even put a handheld code reader on it and got the VP44 code indicator...BUT I didn't rush out and buy a new VP... I did, however, replace the fuel filter, thinking that maybe I had some water or dirt in it.
After that one tank of fuel in the aux tank, I removed it and didn't use if for the next tank or two. The truck ran and performed perfectly fine; fuel psi and all was normal as could be and always was.
Then, I decided to take a short trip and opted to put the aux tank back on. Sure enough, after about 1/2 a tank, the Commander started showng dropping fuel pressure, I had the hesitant accelaration--this time I was 200miles from home. So, thinking I might have something wrong with the aux tank, I stopped and topped off the main tank with fuel, turned off the aux tank valve, flipped open the fuel/water separator switch, drained the filter, refilled the filter housing, and got back on the road. The truck still accelarated so-so, and the performance eventually 20-30 miles returned.
Later, as I neared home, I was able to use the remainder of the aux tank fuel with no issues. I cleared the VP code. Every thing "seems" normal now, but I'm afraid to use the aux tank.... Questions:
(1) Could the used aux tank have had some fungus in it? I put some biocide in it just in case...not sure if that stuff works or not
(2) Could the VP be going bad? Afterall, I do have about 100K on it...but the truck is performing just fine and the fuel pressure is great. I've run 4-5 tank full since those incidents and all "seems" fine...
(3) Each incident occurred when the aux tank was in use. I bought a new "pressure-vent" cap for it...could the old (used) vent cap have been causing a pressure problem? ((the tank does not have a pressure valve on it))
(4) am I paranoid? --dan

Copenhagenjunkie

I don't think a pressure vent cap will work. You need a vent to let air in as fuel is being pulled from the aux tank. It's causing a vacuum issue, that is your problem. Try leaving the cap loose.

carl48

i vote for paranoid. the vp44 and lift pump seems to have that effect on people. the tank is not the problem. make sure you have your gauge hooked up after the filter and not before. and the commander sending unit will have massive amount of failures if you do not use a snubber on it. best to remote mount it to the firewall

danalex

Vent: I was actually thinking that might be the problem. Do you know of some sort of "after market" vent-valve that I can install on the tank? Obviously it would involve drilling a hole...so I wanna make sure there are no fumes or residual stuff that could go boom...

As for the Commander, I have the newer sending unit (agree the original release had serious issues); it is mounted after the filter right near the injector.

Thanks yall!

johnh

what kind of cap do you have on now? on my aux tank i have a vented cap i found in a junk store......it has 2" pipe threads, it fits and works perfect