Aux Fuel Pump Problems

[AlterKnight]

I installed a Front Runner 45 gallon auxiliary fuel tank in my Land Cruiser. The FR install just re-fills the main tank and doesn't have it's own gauge or can be switched to supply the engine directly.

This is a crude schematic of things and the dual filler neck:

My problem is that the aux fuel pump, rated at only 2 amps draw, is blowing 15 and 20 amp fuses. The pump is directly wired to the battery via an OEM switch. But the plot thickens:

- pump/fuse works fine with the truck off (I can operate it as it's direct wired to the battery
- pump/fuse work fine while the truck is idling
- 15 amp fuse blows within 20 second when operating the pump while driving
- 20 amp fuse blows within 5 minutes when operating the pump while driving
- 25 amp fuse doesn't blow when driving

My trusty mechanic put in a relay and it appears to have fixed things as I could drive using the pump with a 20 amp fuse.

However, I am still wondering if this was the real fix or a bandaid, covering something else us. I am wondering of increased fuel pressure while driving is causing the pump to draw such high amperage. However when I look into the filler neck while fuel transfer is happening the pressure looks reasonable. But then again I have the gas cap off so pressure would be relieved.

Thoughts?

 

[damaged110]

i have the same set up. my pump started blowing fuses after a month. the pump was overheating and pulling to many amps. i replaced the pump and have not had an issue again and it have been 4 months. the pumps that comes with the kit are not the greatest anyway. i would invest in a new pump so you dont end up with a tranfer pump that dies on you while you are in the middle of know where like mine did.

 

[AlterKnight]

I am on my third pump. The first one died with weeks. The second, replacement from Front Runner, I killed by accidentally running it dry. This one, a rotary style, is from another manufacturer, but the one blowing fuses.

 

[blupaddler]

I didn't have the Front Runner, mine had the Lone Ranger. But the set-up should be the same. The pump transfers fuel from the aux. tank to the main tank via the breather line...


I personally would get a new pump. Don't be too concerned about fuel pressure, you don't need a high pressure EFI one.

I initially used a nice Carter pump from Summit Racing. It worked good and had a nice humm when operating. It was lower pressure, but had a higher output (gpm or something like that). It worked great but I mounted it in a bad spot, and it got crushed by the rear axle on uptravel (on the second day of a three-week trip in Baja). I would have bought one again, but at $100, I didn't want to risk it again...

The second time around I used a cheap (read: slow, but effective) one from Napa. This one lasted for years. Focus on one that has a good output. The Napa one was a generic pump. But well worth the $30 or so, I even carried a spare... just in case. But never needed it.


Hope this helps!!!
My aux. tank was one of the best investments...

 

[Mike S]

I have a twin tank with parallel aux feed to a electrically switched valve in the engine compartment. This uses a Mallory 60FI (high pressure) electrical fuel pump and 30 amp relay. Mallroy install specs call for a 15 amp fuse. I expect that the draw is around 10 amps.

This pump has been working very well for over 10 years. No blown fuses.

 

[AlterKnight]

Put in a relay and pump seems to be working fine with a 20amp fuse - not blowing so far.

 

[AlterKnight]

Ok, relay didn't fix it. Blowing fuses up to 30amps.

Going to check the wiring on Friday to make sure it's not rubbing somewhere causing a short, however suspect internal tank (aux or main) while diving is causing the pump to draw more amps (it's only rated to draw 2amps!).

I am on my third pump - the first two were Front Runner, but this is a pump I got from O'Reilly Auto.

Any suggestions on what the heck is causing this?

 

[ntsqd]

What gauge are the wires and where is it grounded? Check the voltage at the pump compared to it's own ground and again compared to direct battery ground.

Is there filth in the tank? How about the filter between the tank and the pump? (sounds like the pump is external)

 

[AlterKnight]

What gauge are the wires and where is it grounded? Check the voltage at the pump compared to it's own ground and again compared to direct battery ground.

Is there filth in the tank? How about the filter between the tank and the pump? (sounds like the pump is external)

Not sure on the gauge wire, but will check tomorrow when my mechanic and I re-look at things. The last time we replaced the pump the filter was a bit dirty but nothing major - it is an external pump.

 

[AlterKnight]

After looking over everything again, and re-visiting when the fuses are blowing and pumps have been burning out, my mechanic and I concluded the location of the pump is causing the problem.

It's externally mounted on the backside of the tank and at the tank's mid level line. When the tank is full, the pressure of fuel in the tank feeds the input of the pump without a problem. I haven't had any problems transferring the first 20 gallons or so from aux to main when the aux is full (it holds 45 gallons). However when the aux tank is half full or less (red line in drawing), we believe there isn't enough pressure and/or the pumps we have been using don't provide the suction necessary to continue to extract fuel. So as the pump works harder and harder to transfer the last 10 gallons or so of fuel, fuses blow, or if I have a big enough fuse in there, the pump eventually burns out.

I am not sure why this isn't a problem for other Front Runner owners, unless this was a design change recently.

My mechanic and I think there are two solutions: lower the pump to be level with the bottom of the tank or purchase a pump that has enough suction power to deal with being mounted at the mid line of the tank.

 

[viter]

I might be wrong but in my opininion the location of the pump should not matter as long as it is somewhere between output from tank and input into filler tube. the pressure necessary to pump would be the same no matter where the pump sits - is should equal (difference in height between the fuel level in tank and your output point in filler neck) multiplied by acceleration of gravity and multiplied by the density of fuel, plus add any internal pressure resistance due to the transfer tube diameter, bends in line, pump internals, etc.. None of these variable change (except for maybe bends in line) as you move the pump up and down within the tank height range, so I think pump location is not important.

 

[AlterKnight]

Well I have never blown a fuse or had a problem transferring fuel from aux to main when the aux was completely full. However, I consistently have problems with transferring the last 20 gallons or so.

Given this trend, what else could it be other than what I am theorizing?

 

[ntsqd]

Characteristically electric fuel pumps do not suck as well as they push. Common advice is to mount the external pumps as low as possible, below the bottom of the tank is preferable.

If there is a filter/sock on the in-tank pick-up I would suggest inspecting it for debris. You could be experiencing a summation of a bunch of little things, and the lower fuel is the proverbial straw.

 

[AlterKnight]

We have been looking at the inline filter and while there is some noticeable debris being filtered, it certainly doesn't look like too much that would cause a blockage, or at least significant impediment flow.

I told my mechanic this afternoon that we should re-test things with a known working pump. We did try to pump some gas from a small container held below the pump (simulating the illustration above), and despite hearing the pump turn on, we weren't certain the pump wasn't already fried. I think such a test would confirm our theory that the pump can't draw fuel from below it, or at least very effectively.

 

[johnhughes051]

I put an elec.cutoff valve before a filter and then the pump. It goes into the filler pipe and fills the main tank in about an hour while driving. As I was afraid I might forget it was on I put in a timer switch which I can set from a few min. to an hour. Works great!