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Diagnosing dual tank balance module

Damn, I thought the site was down all week and I missed out on great excitement in this thread.

INdeed, front sender and rear sender only give info to the balance module.

Balance module reads both, and energizes rear xfer pump when front is lower than rear by 2 gallons or so, and fills it about 2 gallons higher, this ensures rear runs out first.

Then the Balance module (which is a computer board inside) I think takes an average of the 2 tanks to send to the gauge. This is all based on the info I've dug up, not sure if facts or not.

However, I am unable to read the purple output wire as ohms to my fuel gauge.

Nothing in the above tests mentions I should be able to though, something about a wavelength signal or something?

Look forward to your next post Hydruak.

Also, when your rear tank is empty, can you please unplug the balance module and check for ohms on rear signal wire? (2nd one in, next to pink +12v).

And if you could, i know its harder, check the rear tank wire when its plugged in. Once again when tank is empty.


Also, can you check your front tank for OHMS, and fuel gauge reading (if its working), Both unplugged from the module and plugged in? See if they are the same.

Thank you very much, and welcome to the Site (and my lonely thread!) Glad to have some more peeps in here! I'm glad my research has helped you. And I don't mind being called mark, I've been called MUCH, MUCH worse :)
 
Hydrauk said:
Hello All I am new here. I have been watching this post in the past few days.
I learned ALOT form reading Matt Bachands posts. Thanks Matt!!! It helped out alot. But I still have a "Pegged" fuel gauge when truck is on/running.This truck is a: 1996-97 GMC K3500, Mason dump, 6.5 Turbo, Dual tanks, 4WD, Automatic. Here is what I did so far:

1. I removed and cleaned every Ground connection I could find in the Engine compartment.(Engine,Firewall,etc) I used a angle grinder with a scotchbrite pad. They all shine better than new and are tight.

2. Did the same as above with Battery connections.

3. Cleaned and Re-grounded connection near the front fuel tank. (It comes out of the wire harness with the fuel sender connection)

4. I checked the Oil Pressure switch and Relay. Seems to be operating. 10-20 PSI at Idle HOT. 30-40 PSI at Idle COLD.

5. Checked and cleaned Relays and other connectors on firewall. I did find one real bad connection, which I repaired. Hoped it may "Fix" everything type of find!!!!!!:nonod:

6. Checked Charging system. Got 14.4 Volts when running. One of the batteries seems to be going bad though.

NEXT:......Fuel Module located in frame rail under Driver seat:

1. Removed Module and inspected it. Took apart as well. Seemed clean and dry.

2. Term "A" Pink: Has 12 Volts with key on run.

3. Term "B" LgtBlue: 52.8 Ohm reading. Tank is about half full +/- (Rear)

4. Term "C" DrkBlue: 89.1 Ohm reading. Tank is damn near full, I filled it. (Frnt)

5. Term "D" LgtGreen: With engine running I grounded this wire, The relay did indeed "click" and the Rear pump ran fine.

6. Term "E" BlkWhite: Checked for Ground using meter and test light. It tested Good.

7. Term "F" Purple: With key on, I Grounded this wire, gauge went from "pegged" to the Full mark not Empty mark. When I took off the ground, the gauge went back to "pegged"

So it seems to me that the Fuel module IS working. Both fuel pumps checked good. All other tests that I performed passed.

I then removed the Gauge cluster. Inspected the Circuit board, and the molex connecter. No damage or breaks. I traced the Fuel gauge connection to the molex connector (Gnd, pwr,and signal). I then tested for continuity between the connector and the purple wire at the control module. It tested Good. I tested the Grounds at the Molex...they tested Good. Shows no breaks in the wires.

I cleaned the connector with Electrical cleaner and blew it out with compressed air. Re-installed the Cluster.

So after performing all above work in detail..Iam very meticulis!! I still have the "pegged" Fuel gauge. It actually Vibrates a bit when it's pegged.
So here you have it....Iam Stumped.....and getting irritated.

I suppose the Gauge must be at fault..or Maybe a Battery is going bad?

Anything I looked over? Any Input? Any more tests? Anything at all in relation to this problem?

I want to keep this truck interior all Stock. No aftermarket Gauges.

Would a Fuel Gauge from a GAS powered truck work? I saw 4-5, 95-98 Gmc/Chevy trucks at the bone yard last Saturday. The interiors where all MINT. They are Cash for Clunkers. What size are those Torx screws that hold the gauge on...seem real small.

Thanks in advance for your time!! Please anyone out there with input greatly accepted. Cheers!!

David D.
Click to expand...

Apparently the purple wire goes sraight to the gauge, but I have had no luck checking it for Ohms, what do you get?
 
Matt Bachand said:
Damn, I thought the site was down all week and I missed out on great excitement in this thread.

INdeed, front sender and rear sender only give info to the balance module.

Balance module reads both, and energizes rear xfer pump when front is lower than rear by 2 gallons or so, and fills it about 2 gallons higher, this ensures rear runs out first.

Then the Balance module (which is a computer board inside) I think takes an average of the 2 tanks to send to the gauge. This is all based on the info I've dug up, not sure if facts or not.

However, I am unable to read the purple output wire as ohms to my fuel gauge.

Nothing in the above tests mentions I should be able to though, something about a wavelength signal or something?

Look forward to your next post Hydruak.

Also, when your rear tank is empty, can you please unplug the balance module and check for ohms on rear signal wire? (2nd one in, next to pink +12v).

And if you could, i know its harder, check the rear tank wire when its plugged in. Once again when tank is empty.


Also, can you check your front tank for OHMS, and fuel gauge reading (if its working), Both unplugged from the module and plugged in? See if they are the same.

Thank you very much, and welcome to the Site (and my lonely thread!) Glad to have some more peeps in here! I'm glad my research has helped you. And I don't mind being called mark, I've been called MUCH, MUCH worse :)
Click to expand...

Matt,
Hello and Thank you. I will do those tests for you in the comming weekend. So far as of Yesterday driving around, my Fuel Gauge is reading a little lower than before, showing Iam using Fuel. So...I think it may be working now. We shall see.

Although the gauge cluster itself from the gasser LOOKS identical, once I plugged it in some of the Gauges where Off, In different ways. The tach was WAY off. The only Gauges reading right or close to normal where the Fuel,and Water temp. So I Disected MY cluster, and replaced the approiate Gauges for my needs. Taking the Cluster apart is very Easy.

My Temp gauge used to read 190 or so, Now it reads at 210. I checked Antifreeze level, Iam good. Is 210 the correct reading?

My Volt gauge used to "flutter" just a tad, when I used Turn Signals, It no longer does that. Good!

I used to have a small "light" on up in the left hand corner of the cluster, Only would go off if I put Headlights on. It was on all the time otherwise. That little light no longer is lit. My Headlights and running lights work fine. I wonder if that light had a purpose???? It was annoying anyway.

I will TRY to get some pictures of taking the Gauge cluster apart. I will tell you once it's apart you will see, it could be dirty back there, Hence, Dirty connections, Hence...bad connections...Meaning, could be PART of Faulty Gauge readings!! Mine was dirty in deed.

Will update soon.

Cheers!
 
That little light is the daytime running lights. Do they still function?

I think my factory fuel gauge lost its 'home base' seeing how you just took it apart, does it seem possible that something got loose so it no longer has a locked Full, and locked empty? it seems to float all the way around doing multiple 360's over the months.

Cheers to you!

Factory t-stats are 195's, so the 210 is probably wrong, but the only way to be sure is to double check with a scanner. FWIW on that subject, you never want to run your 6.5 in the 220's + range, even though the gauge gets red at 260. Risking major block damage via cracking.
 
Matt Bachand said:
That little light is the daytime running lights. Do they still function?

I think my factory fuel gauge lost its 'home base' seeing how you just took it apart, does it seem possible that something got loose so it no longer has a locked Full, and locked empty? it seems to float all the way around doing multiple 360's over the months.

Cheers to you!

Factory t-stats are 195's, so the 210 is probably wrong, but the only way to be sure is to double check with a scanner. FWIW on that subject, you never want to run your 6.5 in the 220's + range, even though the gauge gets red at 260. Risking major block damage via cracking.
Click to expand...

Hello Matt,
Ok I will look into the Thermostat today. Thanks for the Tip! My Daytime light never worked anyway. I need to go to the Auto yard today, Maybe I will get a Headlight switch, from a newer year gasser...see if it makes a difference.

I remember..The Fuel gauge I took off the Gasser cluster was slightly "resistive" in movement. The Gauge I removed from MY cluster was really lose and would move freely like a Compass needle. So keep that in mind.

My Fuel Gauge is just about reading half tank, I have some driving around errands to do today...should use up some of that Fuel. I will keep a close eye Gauge changes.

If all goes well today, I should be able to do those tests you requested, On Sunday AM. Got Football to watch in afternoon.

Cheers!
David
 
Hydrauk said:
Hello Matt,
Ok I will look into the Thermostat today. Thanks for the Tip! My Daytime light never worked anyway. I need to go to the Auto yard today, Maybe I will get a Headlight switch, from a newer year gasser...see if it makes a difference.

I remember..The Fuel gauge I took off the Gasser cluster was slightly "resistive" in movement. The Gauge I removed from MY cluster was really lose and would move freely like a Compass needle. So keep that in mind.

My Fuel Gauge is just about reading half tank, I have some driving around errands to do today...should use up some of that Fuel. I will keep a close eye Gauge changes.

If all goes well today, I should be able to do those tests you requested, On Sunday AM. Got Football to watch in afternoon.

Cheers!
David
Click to expand...

Great, btw, the daytime running light module is inside the cab by your left foot. there is a little access/fuse panel. The DTR module is the bottom left one i think.

If you manually moved the fuel gauge with your finger, does it have stops at full and empty? Is it a physical attachment? or a limitation of the needle? Is it possible for teh entire assembly to 'pivot' on the needle's center, and rotate?

My fuel gauge is currently pointing south, to my oil pressure gauge. Its all screwed up.

Same here for Sunday Afternoon :) I would never ask of anyone to do anything else but watch the games! (Even the Cowboys'!)... We got some sushi to eat up in my neck of the woods :)
 
Matt Bachand said:
Great, btw, the daytime running light module is inside the cab by your left foot. there is a little access/fuse panel. The DTR module is the bottom left one i think.

If you manually moved the fuel gauge with your finger, does it have stops at full and empty? Is it a physical attachment? or a limitation of the needle? Is it possible for teh entire assembly to 'pivot' on the needle's center, and rotate?

My fuel gauge is currently pointing south, to my oil pressure gauge. Its all screwed up.

Same here for Sunday Afternoon :) I would never ask of anyone to do anything else but watch the games! (Even the Cowboys'!)... We got some sushi to eat up in my neck of the woods :)
Click to expand...

Matt...Thanks for the info on the DTR module, I shall look at it later this morning.

I decided to replace the Thermostats, just to be safe. When I removed the housing it had two different thermostats. I put 190's back in, Those Thermostats aint cheap!! Truck runs around 200, I think it's ok. The gauge may be slightly off.

Ok...The Fuel gauge, when I moved it with my finger, had resistance. It did not have stops, at either end. If you held the Gauge in your hand and gave it a slight wiggle, It would barely move. The gauge I replaced...If you wiggled it...the needle would flop and swing all over, like it was really loose.

I hope that help on the description.

Yeah...I like to sit back and watch the games....Usually after 1:00 in the afternoon, I am having beers, wings and Football. Sushi eh? I actually love the stuff! It's the cowboys...well..thats a different story...:D
 
Hydrauk said:
Matt...Thanks for the info on the DTR module, I shall look at it later this morning.

I decided to replace the Thermostats, just to be safe. When I removed the housing it had two different thermostats. I put 190's back in, Those Thermostats aint cheap!! Truck runs around 200, I think it's ok. The gauge may be slightly off.

Ok...The Fuel gauge, when I moved it with my finger, had resistance. It did not have stops, at either end. If you held the Gauge in your hand and gave it a slight wiggle, It would barely move. The gauge I replaced...If you wiggled it...the needle would flop and swing all over, like it was really loose.

I hope that help on the description.

Yeah...I like to sit back and watch the games....Usually after 1:00 in the afternoon, I am having beers, wings and Football. Sushi eh? I actually love the stuff! It's the cowboys...well..thats a different story...:D
Click to expand...

Sushi, yep, thats what we're gonna make of the Dolphins!
 
Matt Bachand said:
Sushi, yep, thats what we're gonna make of the Dolphins!
Click to expand...

Matt,
Hello. I MAY not be able to do the Fuel sender checks today. I sure will try though. I used up more fuel, and gauge is reading A little under Half.

I will be batteling, on removing a Crank Position Sensor. I went to pull it last night, because the wires going into it are all broke/frayed. Anyway...the hold down tab broke off the sensor. So..I will be playing with that today.

If all goes well..I will...do the tests. Enjoy your game!! I might miss the first round of games anyway...:nonod:

Cheers!
 
Hello..Matt...and who ever is reading this thread.

Well Matt...Yesterday...I was running around doing errands, My Fuel gauge was reading just about 1/4 tank. I was happy...and truck has been running fine. BTW on Wensday....I replaced my Primary Lift pump, and The OPS. Just to be safe.

OK...so...driving down I-95 last night...Truck was running fine...Then..it stutters...and stalls. Pulled over...waited a few seconds...started up..I was lucky..right near an exit.

It ran...to the next light...looking over at the BP Diesel sign. It Stalled at the light...DAMN!! Cranked it...few seconds...it started...floored it to station pump. I decided to put Fuel in the PRIMARY Tank. I did not fill it all the way....Just about 15 gallons. I am Damn sure it was near empty. Just wanted enough fuel at the time to "See" what is going on here..

I attempted to put Fuel in the REAR tank...Wouldn't take Fuel...It was FULL!!

Truck Started...and ran fine. I drove it around and even made a few stops. No more stalling, and it started up every time.

So what now? I already fully Tested the Fuel Balance module..as stated in one of my past posts. It tested good.

I am figuring...Ok...Test the Balance Module and relay...and x-fer pump AGAIN!! But i am beginning to suspect...the REAR sending unit is at fault!

WHY?...Well I would figure if it shows the Balance Module...that the Rear tank is empty...then...it will obvisouly...not transfer fuel into the front tank...make sense?? ANY thoughts??

Another question:

Found it strange..The truck stalled a few times, put fuel in it...and now it seems fine. ANY Diesel I ever owned...when you ran out of Fuel...It was a pain!! Bleeding...etc.... So what happened here?

I should be able to look it over later this morning. We are expecting a bit of a Nor'Easter starting today. Wind this mornin is already smokin out of the East!! So I should post results tonight or tomrrow.

Let me know what you think...I hope we can figure this Fuel balance, Gauge thing out and be done with it. Hell...maybe even be experts in that dept...:rolleyes5:

Cheers..
David
 
Have you guys ever thought about getting rid of the balance module, and just running a tank selector valve? JC Whitney has one that will switch between tanks, also will change fuel pumps, and can also switch the readout on your guage to either tank. It shouldn't require too much plumbing or wiring to do either. Just go to jcw.com, and search for fuel tank selector. They have two. One with 3 ports, and one with 6. Only $83.
 
The way this system works, the rear lift pump only pumps the fuel to the front tank, so said switch wont work there. I'm probably going to wire up a lighted toggle switch just to xfer the rear tank, but then need a 2nd gauge for the tank so you're not 'dry running it'

Hydrauk, Depending on the foam/baffle type (if any) (I have none) in the fuel tank when I run out of fuel it always sputters, and usually can recover in limp mode, no stall.

It doesn't worry me any because i have a 40 gallon tank on the bed I can pump into to, so I always keep 10 gallons in there.

Diagnosing my gagues i've run out a few times... hey, its the only way you know where Empty truly is!

The system doesn't get fully airbound or anything, it just dies, I usually crack the bleeder right after it re-fires and it lets out the little bit of air, but I think the IP can work some air out itself fairly easy, based on unexplainable fuel pressure readings and hiccup/miss and then perfect recovery and driveablility after it. Always after running out of fuel symptoms too.

---------------------

1 of 4 things.

Balance module defective, not powering the relay.

Relay defective.

Rear Lift pump defective.

Rear FSU defective or clogged. Could be air in the lines not allowing the joke stocker xfer pump to suck through, could be a clogged sock in the rear tank. Or the Measurement coming out of tank isn't right.


So now you know your rear tank is full. Go unplug that balance module and test the 2nd wire in next to power for OHM's and tell me what it is. Then test the front tank wire (3rd in) for ohms, tell me what that is and what fuel gauge reads.

Now, Plug the balance module harness back into the module, and check them for ohms again. (This is key )... My readings CHANGE when that harness is plugged in. See if yours do please.

Ground the 4th wire in to ground and make sure it CLICKS the Relay. Feel the rear lift pump as you are doing this to make sure its purring)

If its not purring when 4th wire in is grounded, Check for power out of relay-LP connection when Relay is grounded.

--------------------

Now mines acting all odd too, I filled both my tanks, and I let it warm up, and it was leaking fuel out of my vent/fill hose connection. I popped the front fuel tank lid and it spewed out. My rear tank was on prematurely, and it was pressurizing my front...........

I unplugged B-Module harness, and drove 200 miles before plugging it back in again.

I showed OOF symptoms 389miles out of 40 gallons??? Doubt it.

Everytime I fill my tanks they never take anything close to max capacity of tanks...

=============


These dual tanks sure are fun. The best part about working on them is you only know success/failure after you've used up the entire tank, so its an ongoing month after month long thing with em............

Keep the info coming in as I'm dying to read someone else's readings.

Sure is nice to not be alone here :) Sorry you're having problems, but I'm sure glad to have a 'dual tank buddy' lol!
 
with the older style 6 port tank switch you only need one lift pump.it just switches the outlet and return lines. Maybe your transfer tank doesn't have a return line?
 
Just returns to the main tank (front).

Rear sender has 2 lines, and the fill, Supply and vent I assume.

There Is a blocked off tube from the generic mold.

Front has the standard 3.
 
Using that valve from JCW, you could ditch the factory setup and just select which tank you wanted to run off of, instead of expecting it to run on it's own. You could just run off of the first tank, and when you switch to the second tank,you could have the return go to the first tank. The only thing that you would have to be concerned with is if you filled both tanks, but then was running off the rear tank. You would wind up over filling the front tank. Unless you wanted to add a return to the rear tank.
 
Factory plumbing, the ONLY hose the IP can draw fuel from is the front tank. The rear tank has no physical connectinos to the IP what-so-ever, supply or return.

The rear tank simply xfers into the front tank, to allow the same system to keep pulling fuel through the front tank. I dont' see how a switch will help without some major plumbing.

What is easy to do, however, is to just wire up a toggle switch to activate the rear transfer tank. This will pump fuel into the front tank.

Then required would be a second fuel gauge to monitor both gauges, or you'd end up dry-running the rear tank as you'd have no idea how much fuel is in there.

I probably will end up going this route with the toggle and 2nd fuel gauge. I will hold off till next year though. I learned last year that fuel problems are not fun compounded by the temperature factors that start to play.

For this winter I'll run my front tank, and I'm use to my backwards fuel gauge now, I don't even see the 'f' to me it says 'E'. :)

I thought glowshift was all cool with their own tech forum... Been almost 3 weeks and no response.............
 
On the older gm switches it allowed you to run your lines from the engine to the switch and then from the switch to each tank also the sending unit wires ran to the switch and when you flipped your switch on the dash it also switched the sending units so guage would read from the tank your using.
 
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