Aux tank fuel pump saga continues

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Appears so. I haven't tried it with the truck idling, but it definitely works fine when the engine is turned off and just 15-20 seconds when driving. '
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So would a relay fix this?
 
You are either backfeeding something when the truck is charging, or you are pumping against the fuel pressure of the truck when it is running. Maybe you are plumbed into the return line on the main tank. Run a wire from the battery to the pump with a fuse, and ground the pump at somewhere (ie, hotwire the pump). See if behavior changes. It is does not blow the fuse, the problem is in your wiring, if it does, the issue is plumbing.
 
Christo, I was there during the install and am 100% certain it's plumbed right. I tried the pump while the truck was idling and the fuse didn't blow, so it appears to be a problem only when actually driving.
 
I can watch it and estimate it to be around 23 gallons per hour.

I tried a 20 amp fuse, and it lasted about 3-4 minutes before blowing (15 amp fuse only lasts 10-15 seconds). I then tried a 25 amp fuse and it didn't blow. I re-visited the pump's draw, and discovered it's only rated at 2 amps!

Again, the 15 and 20 amp fuses only blow when driving the truck - they are fine when the engine is not on or just idling. We are going to put in a relay tomorrow and then use a 15 amp fuse to see if that is the solution.
 
there is something wrong there ..

1. are you running it' direct from batt with a switch ?

2. if it only use 2amps .. you should use as much as 10 amp fuse ..

I put my bet as same as Christo in the flow ..
 
Here is a very crude, but simple schematic of the the tank install and a pic of the dual filler neck.

As you can see, it would be virtually impossible to plumb things wrong given the diameters of the main supply lines vs the vent lines vs the transfer line as well as the angles of the lines welded into the neck. One main supply/vent point towards the main tank and another main supply/vent point to the aux. And the bent transfer tube/inlet is unmistakable.
Aux Tank Diagram.webp
filler neck.webp
 
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spressomon said:
Even worse then.
Click to expand...

Not given the pump only puts out 4 psi.

The more I research, the more I think it is excessive pressure build up causing strain on the pump. When I open the gas cap, I get more than a normal amount of pressure release. I guess the solution to this would be a vented gas cap, except I doubt I'll find one that fits.
 
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AFAIK just about everyone that has added an aux tank, mine included, has ended up with higher tank vapor pressure at the cap. I assume this is mainly due to not having a larger or dual evaporate canister.

I still don't like how the feed tube appears crimped...they did a poor job bending that tube. Remember: You have an unresolved problem ;)
 
I had the same opinion about the crimp in the tube, however after watching it operate it doesn't appear to be a bottleneck given the low psi of the pump.
 
in the OEM dual tank system are the fuel from the sub tank pushed to the filler tube like yours . ? or maybe it's pushed direct to the main tank or maybe just to the tube but more closer to the main tank . ?
 
It appears as if the relay fixed it. I was able to run it for 15 minutes while driving using a 20 amp fuse - had to stop after 15 minutes because the main was full.

However, I am still not sure if the relay was the real fix or a bandaid covering something else up.
 
TTT - relay didn't fix it - blowing fuses up to 30amps. Seems to blow fuses more when aux tank is half empty vs complete full.

Going to re-look at the wiring Friday to make sure it isn't rubbing and shorting things out. However, wonder about pressure in the tanks causing too much strain on the pump. However, the plumbing is right as supply lines and vent tubes are different diameters and things work at times.

Any suggestions - this is driving me nuts?
 
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