Fuel Gauge Over Power Question

Create a thread to track the progress of you MB/GPW restoration progress. Previously a General Discussion board.
Post Reply
DF-Jeep
G-Private
G-Private
Posts: 4
Joined: Sun Feb 25, 2018 12:21 pm
Location:

Fuel Gauge Over Power Question

Post by DF-Jeep » Thu Mar 01, 2018 6:15 pm

After 3 months of messing around, I still am not able to find the problem to my fuel gauge. I do know that my sender unit, wiring, and ground is all good, but there seems to still be an issue. When I put an OHM meter on the sender unit it registers gradually as you would expect over the entire length of travel by moving the float between empty and full. However when hooked to the gas gauge in the vehicle it only registers near the top say the last 5-10 degrees of motion.

I measured the resistance between the two gas gauge post it is read 206 ohms. I read on one of the message boards that it should be 32 ohms. I am not sure if the 32 applied to a 6 volt system and I am using a 12 volt system. Is it possible that the gauge is bad?

Also I measured the voltage to the gage when the engine is running and it is reading 14 volts. When the engine is off I get 12 volts off the battery. Can the alternator be kicking off too much voltage and causing the problem.

Thanks for your help


Peterdodge6volt
Sergeant Major of the Gee
Sergeant Major of the Gee
Posts: 362
Joined: Tue Apr 19, 2016 9:19 pm
Location: Australia

Re: Fuel Gauge Over Power Question

Post by Peterdodge6volt » Thu Mar 01, 2018 7:27 pm

Hi
Are you running on original fuel gauge,
Second when driving the jeep for 15/20 minutes did the fuel gauge glass get a little frosty like moisture or did you touch the glass if it hot.
If the jeep 12v then you need to use a resistor for the 6v fuel gauge so it won't over power it.
If you don't put resistor on the fuel gauge it will over power it and the needle will read 5/10 % wrong.
You can buy them on eBay.
Cheers Peter

DF-Jeep
G-Private
G-Private
Posts: 4
Joined: Sun Feb 25, 2018 12:21 pm
Location:

Re: Fuel Gauge Over Power Question

Post by DF-Jeep » Fri Mar 02, 2018 5:42 pm

We are using a new 12v fuel gage with an inline resister that we just added.

Wolfman
G-Lieutenant General
G-Lieutenant General
Posts: 6876
Joined: Sat Jan 12, 2008 5:25 am
Location: Tipton,In.

Re: Fuel Gauge Over Power Question

Post by Wolfman » Sat Mar 03, 2018 5:34 am

There has been a world of problems with trying to mix & match OEM and aftermarket fuel gauge components.
Usually does not work, as you have found out. Best to change the sending unit and gauge as a set.
As for what the resistance through the gauge and sending unit should be ??? I don't know. I have heard of readings being all over the place.
An in line resistor between the gauge and sending has worked for some. In your case, you may need more resitance to get the reading down to where it should be.
There has been discussions about 6 and 12 volt making a difference. ??? Again. I don't know.
Science experiment:
Set a 6 volt battery into your jeep and turn the key on. See what happens.
Won't hurt anything and you can see if this makes the gauge read correctly.
Let us know what happens.
Mike Wolford
CJ-2A
VEP GPW
Comm./Inst. SEL
AOPA ( 50 yrs)
EAA ( 49 yrs)
4th Inf. Div. - 5th Inf. Div. - 2nd Armor Div. - CIB

Marty, SoCal
G-Lieutenant General
G-Lieutenant General
Posts: 6319
Joined: Thu Mar 09, 2006 10:34 am
Location:

Re: Fuel Gauge Over Power Question

Post by Marty, SoCal » Sat Mar 03, 2018 4:00 pm

Make sure you have a good ground to the case of the gauge, too.

Some aftermarket gauges have a third ground stud. Also, if the dash has paint where the gauge mounts then the case might not be getting a good ground, you an scrape the paint off where the gauge case touches the dash if that is what is happening. If ultimate originality is not an issue, on a two wire OE style gauge you can solder a grounding wire to the rear of the case and connect it to a known good ground.

You can check for a good ground to the gauge case with a multimeter set to low DC volts, touch one lead to the case of the gauge and the other to the battery negative terminal, should read less then +/- .2 volts, usually even less than that, with the ignition on.
43 Ford GPW 92098
53 Dunbar Kapple M100
Sold: 61 CJ-5, 41 T207 WC-1 Dodge closed cab pickup
MVPA #8266
USMC Tanker (1811, 1812), 85-93
ASE Automotive Master tech, former Chrysler-Jeep Level 4 Mastertech, CA state EA smog license

Wolfman
G-Lieutenant General
G-Lieutenant General
Posts: 6876
Joined: Sat Jan 12, 2008 5:25 am
Location: Tipton,In.

Re: Fuel Gauge Over Power Question

Post by Wolfman » Sun Mar 04, 2018 5:17 am

I am thinking DF has an unbalanced gauge, Marty. He said it only has 2 posts. Balanced gauge has 3.
In this case, the fuel gauge is an ohm meter, set to operate in a single range. Instead of having numbers on the gauge face, it says "E" and "F".
The sending unit has to have a resistance range that matches the gauge range. For example, if the gauge range is set to read 50 to 100 ohms but the sending unit range is 25 to 75 ohms, the gauge and sending unit ranges do not match and the gauge will not read correctly.
This is only an example.
I picked those numbers out of the air.
Mike Wolford
CJ-2A
VEP GPW
Comm./Inst. SEL
AOPA ( 50 yrs)
EAA ( 49 yrs)
4th Inf. Div. - 5th Inf. Div. - 2nd Armor Div. - CIB

Marty, SoCal
G-Lieutenant General
G-Lieutenant General
Posts: 6319
Joined: Thu Mar 09, 2006 10:34 am
Location:

Re: Fuel Gauge Over Power Question

Post by Marty, SoCal » Sun Mar 04, 2018 6:25 am

A two post gauge grounds through the case its worth checking for a good ground to it.

Read EJBs excellent post on how to repair a fuel gauge and you will see that the two post gauge needs a good ground to the case both inside the gauge itself and outside to the dash for it to work properly!

http://g503.com/forums/viewtopic.php?f=4&t=118652
43 Ford GPW 92098
53 Dunbar Kapple M100
Sold: 61 CJ-5, 41 T207 WC-1 Dodge closed cab pickup
MVPA #8266
USMC Tanker (1811, 1812), 85-93
ASE Automotive Master tech, former Chrysler-Jeep Level 4 Mastertech, CA state EA smog license

Wolfman
G-Lieutenant General
G-Lieutenant General
Posts: 6876
Joined: Sat Jan 12, 2008 5:25 am
Location: Tipton,In.

Re: Fuel Gauge Over Power Question

Post by Wolfman » Mon Mar 05, 2018 5:16 am

Thanks for the link Marty. First time I looked at this one.
Old jeep gauges are balanced units, With two post and case ground is a factor. Got it.
Still. you can't mix & match sending units.
With the two coil balanced unit, one coil is a fixed resistance to ground and the other coil is a connected to the sending unit, which is a varible resistor and the range of operation between the second gauge coil and the sending unit must match for the gauge to read correctly.
The reason folks trying replace the sending unit and keep the old, original gauge have problems.
Mike Wolford
CJ-2A
VEP GPW
Comm./Inst. SEL
AOPA ( 50 yrs)
EAA ( 49 yrs)
4th Inf. Div. - 5th Inf. Div. - 2nd Armor Div. - CIB

DF-Jeep
G-Private
G-Private
Posts: 4
Joined: Sun Feb 25, 2018 12:21 pm
Location:

Re: Fuel Gauge Over Power Question

Post by DF-Jeep » Mon Mar 19, 2018 4:04 pm

Sorry for the late reply guys, thanks for all the help. I guess I will match the gauge and sending unit first then will try the other suggestions. Thanks again

DF-Jeep
G-Private
G-Private
Posts: 4
Joined: Sun Feb 25, 2018 12:21 pm
Location:

Re: Fuel Gauge Over Power Question

Post by DF-Jeep » Mon Mar 19, 2018 5:58 pm

Thanks everyone for your comments and suggestions. Here are some answers to your questions which I hope leads to more ideas.

1. I bought a new 12v gas gauge and sensor unit.
2. With the gas gauge wired into the jeep, and the sensor unit out of the tank, I can move the sensor unit up and down by hand and the gas gauge registers properly.
3. When I install the sensor unit in the tank, it registers empty even though the tank is full of gas.
4. As a separate check, with the gage installed in the Jeep, and the new sensor unit in the jeep, I disconnected the wires from the sensor unit and connected the same wires to a second sensor unit (my original) outside the tank. Again the unit outside the tank works when I move the float up and down, but the sensor unit in the tank registers empty. I have also reversed installing the original sensor unit in the tank with the same outcome, it does not work in the tank.
5. Is it possible that there is a mechanical block inside the tank? I can't see any. Is it possible that the sensor unit shorts out when mounted to the tank? But if that were the case, I would think it would register full.

I welcome any new ideas. This has been a real challenge.

Wolfman
G-Lieutenant General
G-Lieutenant General
Posts: 6876
Joined: Sat Jan 12, 2008 5:25 am
Location: Tipton,In.

Re: Fuel Gauge Over Power Question

Post by Wolfman » Tue Mar 20, 2018 5:40 am

Two things come to mind.
1. - the float doesn't float. Sinks to the bottom.
2. the tank and sending unit is not grounded properly. With a bad tank and/or sending unit ground, the gauge will read empty.
Just because the sending unit is installed in the tank, doe not mean it has a good ground to the tank.
Both tank units must be OK. They work out of the tank by hand.
One more. If I were you, I would go buy a lottery ticket. Your replacement sending unit works correctly with the original gauge.
Mike Wolford
CJ-2A
VEP GPW
Comm./Inst. SEL
AOPA ( 50 yrs)
EAA ( 49 yrs)
4th Inf. Div. - 5th Inf. Div. - 2nd Armor Div. - CIB


Post Reply

Return to “MB GPW Restoration Projects”

Who is online

Users browsing this forum: No registered users and 45 guests