EXPERT ADVICE NEEDED!!!!!

2004 GMC T7500 is drawing fuel unevenly from driver/passenger saddle tanks. Anyone experienced this? What was the culprit and fix?

[@scotthovi]

Put a equaliser hose at the bottom of the tanks

[@canadianconcretepumper1979]

Definitely something I am considering. Even from new this truck was never quite right in terms of fuel draw (ran it out of fuel with 1/3rd of a tank showing on the gauge way back when it was near new).

[@ConcreteFloorSolutions]

That is what we always used to have on our trucks, approximately half inch hose going from the bottoms of the tanks to equalize. Mental note if you park overnight on a crazy angle, the fuel can overflow out of the other tank.

[@canadianconcretepumper1979]

That would be my worry with this rig, seeing as our line-pumps all are often setup on steep and/or off-camber grades.

[@MrThatnativeguy]

Id check the flux capacitor, also is your low blinker fluid dash light on?

[@vegetablesouper9379]

Maybe one tank cap is vented and the other one isnt? Just a guess

[@canadianconcretepumper1979]

I’ve tried leaving them closely in place, and no bueno.

[@vegetablesouper9379]

@@canadianconcretepumper1979 BTW...The cleaning hack re: the carbide tipped scraper is a game changer for a guy trying to paint a pump a pump truck! Thanks for that!

[@mitchelldake7203]

Okay i am not an expert on these trucks in particular, but I have seen issues like this on other vehicles and equipment. If the fuel lines are original its probably worth replacing them. Sometimes the seals in the end of the lines start to leak just enough that they can draw some air. Often times though, that causes power loss issues since the fuel is airated. Old fuel lines can also begin to collapse under suction amd you can't tell a lot of the time. Just because the lines are blown out doesn't mean they're staying open when the truck is running and trying to draw fuel. Another thing I've had to do is move the T for the fuel draw into the center of the two tanks. That is my recommendation, replace the lines and go from there.

[@mikeklein318]

I read some of those suggestions and they were great , but let us know what u found was the problem, my was as simple as fuel cap , the breather holes were not large enough.

[@lagresomadsl]

Build one larger tank for the driverside, or passanger side, replace the current tank with a storage cabinet. A pump will always have a shortage of storage space. Move one of the small tanks to the top deck and use it as a spare fuel tank with gravity feed. Perfect setup for that pump😊

[@tomsoil9909]

As long as you don't take it off road, A 3/4 hose, valve on both tanks near the bottom and join them together creating balance of fuel at all times in both tanks. Also larger hoses and fittings on the system will help big time!!

[@kjartanB]

It's got a overly complicated system. Hose connecting them together at the bottom is what I would do and be done with it. Empty out the tanks and put fittings on the bottom of them for a hose and connect them togheter

[@alwaystroubleshootingupgra9511]

Pull off the lines coming out of the sender and put some pressure in the tank which is staying full and see if the suction is plugged.

[@johnnybrophy8229]

You need to get it up to 88MPH and then make sure that the FLUX CAPACITOR is putting out the right power. And if you still have problems give Doc Brown and Marty Macfly a call.😂😅🎉😂😂

[@johnnybrophy8229]

And if BIFF Tanen says that he can Fix it don't let him because he will probably put Sugar into the fuel tank so you will have to take it BACK TO HIM IN THE FUTURE to get it fixed 😅😂😅😂😅😂😂😂

[@420tagalong]

If it doesn't have a crossover tube/line then more than likely the main line that is suction is possibly collapsing when it's drawing fuel from that tank and not letting it draw fuel from it.

[@burtlocc7762]

been told on some late model trucks that it runs on tank till its down ,then transfers from the other.

[@alwaystroubleshootingupgra9511]

Some fuel systems have a “return flow splitter” to equalize flow to imbalanced tanks

[@WoodCutr1]

gotta be a screen, or if theres a crossover tube then im going with the crossover make sure none of the hoses are pinched could also just be how it is, pulls one down then pulls the other, wouldn't really want them connected id imagine, incase one gets punctured you don't want it to dump all the fuel from both tanks

[@canadianconcretepumper1979]

So definitely no crossover between the two tanks (first thing we checked for as our machines which do have crossover occasionally see issues). I’m going to try running it down and see if it eventually starts pulling fuel from the passenger side tank.

[@WoodCutr1]

@canadianconcretepumper1979 just make sure to keep a few cans of diesel and tools to bleed air if it does run dry lol, been there done that!

[@markrobinson6883]

Good luck with that 😂😂

[@randyanderson1983]

I’m having the same issue on my schwing 39 with a 90 gallon tank and a 50 I’ve been to nervous to try and see if it just starts pulling from second tank after main is drained

[@justinwalsh8027]

Sounds like a venting issue to me. Curious if the passenger tank will “get fuller” as the truck runs if you start them both at 1/2 tank.

[@canadianconcretepumper1979]

I may try draining it down to 1/2 a tank on the passenger side to see what happens. 👍🏼👍🏼👍🏼

[@alwaystroubleshootingupgra9511]

Pull off the line at the engine / lift pump and pressurize the tank not dropping and see if fuel makes it to lift pump

[@davidnull5590]

My friends at Google say "A malfunctioning fuel gauge circuit in a 2004 GMC T7500 with a dual fuel tank can prevent the fuel from transferring from the auxiliary tank to the main tank. When the main tank's level is about 25% lower than the auxiliary tank, the fuel pump relay is energized to move fuel from the auxiliary tank to the main tank. The module de-energizes the fuel pump and balance pump relay when the main tank's level is higher than the auxiliary tank's level, or the auxiliary tank is empty." ... "Fuel starvation If fuel return from the injection pump doesn't return evenly to both tanks, the fuel level in one tank can drop below the end of the pick-up tube. The pump will then pull air into the system, causing fuel starvation Fuel pump failure Fuel contamination from moisture, debris, and corrosion can clog critical components like the fuel pump, filters, and strainers To diagnose a dual tank balance module, you can unplug the harness with six wires and use a digital volt/ohm meter to check the following terminals: Terminal A: The pink wire should have 12 volts when the key is in the run position Terminal B: The light blue wire is the signal wire from the secondary (rear) fuel tank. Use an ohm meter to measure the resistance from a good chassis ground to this wire, which should be between 0 and 90 ohms Terminal C: The dark blue wire with a white tracer is the signal wire from the primary (front) tank. Test this terminal the same way as terminal B"

[@canadianconcretepumper1979]

The funny thing is, neither of the tanks has a fuel pump. I’ll check the lines more closely to see if perhaps there is an external transfer pump hiding somewhere.

[@davidnull5590]

@@canadianconcretepumper1979 I've updated the comment; see the last paragraph.

[@davidnull5590]

​@@canadianconcretepumper1979 And this: "Anyone with dual tanks having problems with fuel gauge or the automated balance flow system this may help. This module is located by the front (main) lift pump. Slightly toward the rear of vehicle along the frame rail. On top of this module is a fuel pump balance relay, it turns the rear pump on as needed to transfer fuel. At the module, you have a harness with 6 wires. Unplug it and check the following with a digital volt/ohm meter Terminal A- Pink wire, should be 12 volts with key in run position. Fuse is in underhood fuse/relay center marked IGN E 10 AMP Terminal B- Light Blue wire, this is the signal wire from the secondary (rear) fuel tank, using an ohm meter, measure the resistance from a good chassis ground to this wire and should get a reading between 0 and 90 ohms, 0 is empty tank and 90 is full. Terminal C- Dark Blue with White tracer wire, this is the signal wire from the primary (front) tank, test is same as for terminal B Terminal D- Light Green wire, this wire controls the Fuel Pump Transfer Relay, with the ENGINE RUNNING and the front lift pump working, GROUND this wire, the Fuel Pump Transfer Relay should click and then you should be able to feel the rear pump working. If the relay clicked and pump is not working, connect a test light across the rear fuel pump harness connector and see if you have power. If lighted, then replace pump, if not lighted replace relay providing you have 12v at Terminal A. Terminal E- Black with White tracer wire, This is the ground wire for the control module. Using a test light jump from Terminal A to Terminal E with key on, the test light should be lit. Terminal F- Purple wire, this wire is the output signal to your fuel guage. Gound this wire it should read empty, leave this wire open, the fuel guage will go pass full. The fuel pump relay, which is right above the module, has a wiring harness with 4 wires. They are: Pink Wire is 12 volt from the same source as Terminal A. Light Green wire (thicker gage) is the feed to the rear fuel pump. Light Green wire (thin gage) is the control wire from the module as explained in Terminal D. Gray wire is 12V from the primary pump circuit to energize the Fuel Pump Transfer Relay. Like Reactions:LARRY L DAVIS"

[@canadianconcretepumper1979]

@@davidnull5590 This is awesome information my man. Super appreciative. This gives me lots to work with. I owe ya! 🙏🙏🙏

[@codyx22]

I took a quick look at our t8500 which I believe is a 2001 and there is a booster pump between the passenger tank and frame, I wonder if the people that owned it before us had your problem and this was their fix. Ours is also plumbed a little different than yours. The T isn't in the same spot, it's almost right at the outlet of the drivers tank instead of right next to the filter. But if it was working at one time I would have to assume the plumbing has nothing to do with it.

[@canadianconcretepumper1979]

So we’ve actually had this unit since brand new. Does your T8500 also have Isuzu powertrain? or does it have the CAT powertrain? Whereabouts did you locate the booster pump? I’m wondering if there’s a similar pump hiding from me somewhere on ours… 🤔🤔😁

[@codyx22]

@@canadianconcretepumper1979 Ours is a cat🤮. It's flush with the top of the passenger side fuel tank bolted to the frame rail. I think if yours was in the same spot we could see it at the 45 second mark of your video. I will take some pictures tomorrow and confirm if it looks aftermarket.

[@canadianconcretepumper1979]

@@codyx22 appreciate that brother 🙏🙏🙏

[@jessesloan9636]

Yup,... time to trade it off for a 47m. Its the only proper fix really. I got nothing lol

[@canadianconcretepumper1979]

If by brand new 47m you mean Putz VSP70 loaded up with 47 meters of 2” hose…. you sir are onto something!!!! 😂

[@MaxCrete]

my stupid opinion.... could there be an air lock in the line to the filter from passenger side.... i lnow even changing a filter you have to prime it... whats the manufacturer procedure.....

[@MaxCrete]

i wouldn't bet on running out of fuel to find out about the transfer

[@canadianconcretepumper1979]

So both tanks actually feed into the same, one filter.

[@MaxCrete]

remove 90 try injecting fuel to lin and then put the 90 back on and check....cheapest easiest way

[@Dex01-Z_WingZero]

Its not a DirtyMax! Yeah i got nothing