fuel gauge problem

1941 - 1945, MB, GPW Technical questions and discussions, regarding anything related to the WWII jeep.
majmacs
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Re: fuel gauge problem

Post by majmacs » Thu Mar 02, 2017 11:40 am

Donovan wrote:USAFpj
I will try and answer your question. The dual coil gage is made to be stable where there are fluctuating voltages like we have for jeeps and Other vehicles. The way the gage works is that a coil pulls the indicating arm towards the left side. The other coil on the right side is stronger and can pull the indicating arm to the right side when there is no resistance (when the tank is full). The sending unit is simply a variable resistor and will accomadate the range of 6-14 volts. It's purpose is to reduce voltage on the right coil. So even if voltage is low, the coils still work the same way. I have verified this with a mock setup. The reason the gage has to be different for a 12v system versus a 6v system is the type of wire used in the gage (I think this is a manufacturer standard). A 6v gage has less amperage running through than a 12v gage. So a 6v gage will temporarily work in a 12v system, however the 6v gage will eventually be burned out over time as I think the wire used is smaller than in a 12v gage.

Now back to scheinerj:

What may have happened is that the gage may be wired wrong. If you put the ignition (power) on the sending gage terminal and the sending unit wire on the ignition terminal, the gage will read full and the sending unit position will have no impact on the Empty side coil as the Empty side coil is grounded through the gage case. The Full side coil is normally grounded through the sending unit but now is being grounded on the Empty side coil.

The best way to check the gage is to measure resistance on the terminals. The Ignition terminal to case resistance should measure around 48 ohms, terminal to terminal about 35 ohms, and the Sending unit terminal to case about 80-85 ohms or double what the other terminal is when grounded to case. If you still have problems, the best solution would be to remove both units and bench test the sending unit and gage before putting back in the vehicle. The gage must be grounded in order for the Empty side coil to work.

I have recently gone through the whole process of understanding how they work and I am planning to go into more detail about fuel gages and sending units soon and what is available in the marketplace (with respect to sending units) and how best to get your fuel gage to operate correctly.

Good luck,

Donovan.
Great description, but perhaps backward? Wire gauges in 6v systems are normally thicker to carry more amps than higher voltage systems live 12v, 24v or even 28v in aircraft where weight saving in wire gauge makes a difference. perhaps the failure is from another reason?
Patrick

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Re: fuel gauge problem

Post by scheinerj » Thu Mar 02, 2017 8:04 pm

Going to do some more work on the fuel gage tomorrow.
The wiring is not backwards, tried swapping around the wiring and did not fix the problem.
Double checked the sending unit for function, and it worked correctly.

Will post a picture of the guage as soon as I can.

I don't think it is the kind that requires the spring. It does not have the little bubble on it that the spring goes on.

Thanks.
js

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Re: fuel gauge problem

Post by Peterdodge6volt » Tue Mar 28, 2017 12:14 pm

Hi
I know all about gauge problems
If the fuel gauge stays full all the time, that means the fuel gauge has no earth ground you will need take the fuel gauge out and use sand paper around the hole, if it still says full you will need to pull the gauge aparts and clean the rust on the contact plate inside the case and the case were the contact plate is sitting. Put the gauge back together and put it back on the gauge and will work.
Before when you ready to pull the gauge apart you will need a clamp with rag on the studs to stop from damage thred and when ready to lost the nuts, lost it slowly all other wise it will move studs together and it will break the small wire in side the case stud contact in side the case there is 2 wire on the left stud soldered and the right has 1 wire soldered inside the case studs.
I already have dozens of email from this g503.com club form.
I have help Jack last week, all done and working.
I know all about autolite fuel gauge and other ww2 gauges. Over 11 years and I also restored gauges
I am now restoring 6 Fuel gauge marked ( GAS )
I can get fuel gauge working in 30 minuets on ww2 vehicles by pulling it apart and fix put it back together
And put back on dash board and done.


Cheers Peter.

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Re: fuel gauge problem

Post by scheinerj » Tue Mar 28, 2017 1:20 pm

Peterdodge6volt wrote:Hi
I know all about gauge problems
If the fuel gauge stays full all the time, that means the fuel gauge has no earth ground you will need take the fuel gauge out and use sand paper around the hole, if it still says full you will need to pull the gauge aparts and clean the rust on the contact plate inside the case and the case were the contact plate is sitting. Put the gauge back together and put it back on the gauge and will work.
Before when you ready to pull the gauge apart you will need a clamp with rag on the studs to stop from damage thred and when ready to lost the nuts, lost it slowly all other wise it will move studs together and it will break the small wire in side the case stud contact in side the case there is 2 wire on the left stud soldered and the right has 1 wire soldered inside the case studs.
I already have dozens of email from this g503.com club form.
I have help Jack last week, all done and working.
I know all about autolite fuel gauge and other ww2 gauges. Over 11 years and I also restored gauges
I am now restoring 6 Fuel gauge marked ( GAS )
I can get fuel gauge working in 30 minuets on ww2 vehicles by pulling it apart and fix put it back together
And put back on dash board and done.


Thank you Peter, I will take this advice!
I appreciate your help.

Jordan S.

Cheers Peter.

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Re: fuel gauge problem

Post by scheinerj » Mon Apr 24, 2017 10:06 pm

Well,
I definitely nailed it down to a ground problem.
Took the gauge out of the dash. Wired up and touched it to a ground, and it went from full to the correct gas level.
I then put it in and took it out about 3-4 more times trying to get it to work in the dash. I also sand blasted the bracket, and sanded the gauge housing.
Also sanded behind the gauge, maybe I need to sand that more.

Any tips on getting a good ground in a situation like this?
JS

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Re: fuel gauge problem

Post by scheinerj » Sun May 14, 2017 6:41 am

Okay now I am definitely confused. I drilled and tapped a tiny 8/32 hole to the gauge frame, and added a ground wire,

Still reading full. Now I normally wouldn't be this confused, but last week, I removed the gauge from the housing, powered it up, and touched it to a ground. When I did, It pulled to the correct fuel level.

I grabbed a test light, put one side on the incoming power to the gauge, and then touched to the ground wire, it light up.

I assume obviously i have a good ground right? It looks like the frame is making contact with the gauge housing?

I am stumped, and a little frustrated.

Jordan S.

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Re: fuel gauge problem

Post by Chuck Lutz » Sun May 14, 2017 7:18 am

If you have a two post Autolite gauge then the "U" bracket is isolated so there is no way to ground the gauge that way. You must rely on the SIDE of the gauge near the bezel to ground on the sides of the hole in the dash.

If you have a Stewart Warner gauge with FOUR posts on it then you CAN tie in a ground wire to the "U" bracket. The key here is to stay away from the other two posts.

To me...it sounds like you have an Autolite gauge and there is still PAINT on the side of the gauge right below where the bezel is crimped and right where it will rub against the hole in the dash so the gauge will not ground....
Chuck Lutz

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GPW 108552 4/17/43 Louisville, KY. USA 20371278 (DOD est./Tom W.)
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Re: fuel gauge problem

Post by Mark Tombleson » Sun May 14, 2017 8:09 am

I will agree with Chuck on the grounding issue but it would be wise to post a photo of the front and back of your gage.

When changing from 6v to 12v in MWO ORD G503-W7 they did not change the sender, only the fuel gage. So, back then the sender worked both voltages.

I do not know if modern repo senders are the same but I have seen vendors sell matching sets.

There are lots of threads on the topic.

viewtopic.php?f=4&t=221475

viewtopic.php?f=4&t=118652
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scheinerj
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Re: fuel gauge problem

Post by scheinerj » Sun May 14, 2017 5:42 pm

I sanded the gauge down to the metal previously. The case should be making a proper connection to the frame because when I touched the frame to a bolt, the fuel read correctly. I know I am missing something.

Also, it is a 2 post.

And yes the fuel sender I have is 12 V and 6 volt.

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Re: fuel gauge problem

Post by Peterdodge6volt » Wed May 17, 2017 6:19 pm

Hi scheinerj
Have you sand paper around the dash board to make good contact.
And have you pull the earth brass plate contact back so it can have good earth inside the case which I sent pictures a while ago.

Cheers Peter

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Re: fuel gauge problem

Post by JIMN » Fri May 19, 2017 1:33 am

I would take the gauge and sending unit both out and get them working properly on your work bench before installing them.
Then when you install it back in the jeep you will have a better understanding of the situation.
Once they are back in the jeep don't forget to make sure the jeep body and fuel tank both are grounded to the battery.

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Re: fuel gauge problem

Post by Mark Tombleson » Fri May 19, 2017 1:02 pm

Do you have all the proper bond straps installed? if you are missing any one of the combination of bond straps that ground the various parts of the jeep you may have a issue.

See here: http://www.1944mb.com/article/1033/G503 ... uppression

These bond straps ground the frame to the engine/drive train and from there to the body.

These two go from the body to the frame thru the drive train.

Image

Image
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Re: fuel gauge problem

Post by Chuck Lutz » Fri May 19, 2017 2:35 pm

The ground strap that is needed for the sender is the one behind the air cleaner from tub to steel gas line that goes to the tank and grounds the sender to the tank.

You do need the other ground straps that properly ground the tub in place though!
Chuck Lutz

GPW 17963 4/24/42 Chester, PA. USA 20113473 (USA est./Tom W.)
GPW 108552 4/17/43 Louisville, KY. USA 20371278 (DOD est./Tom W.)
Bantam T3 4582 10/29/42 USA 0173499 (est.)

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Re: fuel gauge problem

Post by Peterdodge6volt » Sun May 21, 2017 1:31 pm

If the fuel tank does not have earth ground that means the fuel gauge will stay empty or 3/4 tank or if the tank is grounded and the fuel gauge reads the same thing then the wire connected wrong way on the fuel gauge need to switch the other way. If the fuel gauges stays full that means there no earth grounded on the fuel gauge or tub or the dash hole where their are paint on the edge. remember the jeep are DC
If the fuel gauges reads different way like fuel gauges is showing half or empty and the tank is full that means the fuel gauges is an AC wrong gauges, the DC and AC rear different.

Cheers Peter

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Re: fuel gauge problem

Post by Chuck Lutz » Sun May 21, 2017 2:58 pm

As suggested previously, remove the sender and the gauge from the jeep.
Wire up the gauge to the sender.
Run a wire from the sender to the NEG on your 6 volt battery
Now run a wire from the gauge to the POS on your 6 volt battery.

1) When you touch it to the POS terminal the gauge needle should move.
2) With the wire to the POS terminal still attached, move the sender float UP and DOWN.

If the gauge/sender/wiring are compatible and correctly wired and working, the needle should move from E up to F when you move the float arm.

Now...You already determined that if you simply ran a wire from the gauge to NEG on the battery and another wire to the POS that the needle moved a bit...if it did not then the gauge is kaput.
Next...If you wired up the sender and the needle moved when the gauge was wired to the POS....but the needle did not climb from E to F when you moved the float are up all the way then they are NOT compatible.

By that I mean that the sender serves to provide resistance (Ohms) to completing the circuit....if it does not come up to F then the sender and gauge are not MATCHED.

If they are not matched then they won't ever read correctly and I suggest you get a Flintstone's gas gauge ....that would be a wooden stick with marks carved on it or send these components BACK.

One last thing....if the gauge seems to read OK in the jeep at E and 1/4 and 1/2 and 3/4 with gas in it but adding more does not move the needle.........perhaps the float arm was BENT? The only way to test that is to remove the gas and since the tank holds 15 gallons, simply pour in 3 1/2 (1/4 tank), then another 3 1/2 (should read 1/2), then another 3 1/2 (up to 3/4 now) and finally the last 3 1/2 (reading FULL now, right?)
Chuck Lutz

GPW 17963 4/24/42 Chester, PA. USA 20113473 (USA est./Tom W.)
GPW 108552 4/17/43 Louisville, KY. USA 20371278 (DOD est./Tom W.)
Bantam T3 4582 10/29/42 USA 0173499 (est.)

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