Another gas gauge issue

[ScottH]

On my 58 Apache, I changed out both the gas tank float and the gas gauge. Both items were purchased new. However the gauge still only reads about 5/8s of a tank when it is full.

Can anyone offer any ideas or suggestions why the gauge is still not reading correctly?

Any info would be most appreciated.

Thanks
Scott

[jremig]

Check your ground wire. If it isn't properly grounded it can make your gauge read faulty.

Joe

[ScottH]

Thanks Joe, was thinking the same thing.

[Russell Ashley]

I would take the sending unit out of the tank and hook it up, and move the float through it's full travel. If it will move the guage to full you probably just need to form the float arm. The float may be hitting the top of the tank before the rheostat is getting to the full position. You will need to ground the mounting ring when you do this.

[zenchal26]

after all that you may need to bend the needle on the gauge to make it right

[mr48chev]

Mr Ashley as he almost always does nailed it right on the head. Zenchal26 came up with one fix.

If it's a factory style sending unit and float you should be pretty close but on after market units you have to make some adjustments to insure that the gauge reads correctly.
Mainly the travel of the float on the float arm has to be unimpeded in the tank and it needs to go through it's full travel. If the float hits the bottom of the tank it won't show empty if the float hits the top of the tank it won't show full. If the float arm is too short it will stay on full too long and then hit empty too soon.

[ScottH]

Thanks guys. Finally had a chance to test ground and pull the float out. The ground is not the issue, ran one from the battery directly and no change. Took the float out and ran it thru the range from empty to full. It appears the gauge is not reading correctly, when I have the float at full the gauge reads about 3/4 full. So the gauge appears to be off at least a quarter of a tank.

The gauge was an NOS I bought off ebay a couple of months ago. I'll try to see if I can adjust it but thinking I may have to find another unit that I know works correctly.

Thanks again for everyones help and input.

Scott

[_Ogre]

ground the wire to the gauge, it should read full
if not, tweak the needle

if it reads full then take a meter to your sensor
it should read close to 1 at empty and 0 at full

[Atomsplitter]

Your gauge and sender may operate thru different Ohm ranges.
Do you have the packaging, it may give the ohm range on the box or paperwork. You can put the model numbers into the internet and search that way too! For example "VDO 301-106" is a 0-90 ohm gauge that requires a sender that operates at 0-90 ohms or the gauge will not read correctly.

[_Ogre]

Tf truck will be 30 ohm
Posted via Mobile Device

[ScottH]

thanks for everyones input. I "adjusted" the gauge and its not perfect but will do for now.
BTW both r 30 ohms.

[wildearp]

Measure the depth of your tank from the flange surface where the sender mounts to the bottom. I measured mine wrong and I have a similar problem........ (this is for cutting a universal sender to fit)

My sender is now intermittent, so I get to drop the tank to change it. I bought a floatless sender from Classic Instruments this time around, but it hasn't arrived yet.

[wildearp]

Gee, I bought that sender in 2012. I installed it Sunday, calibrated and tested it on an empty and full tank out of the vehicle, just like CI youtube video. I tested it twice and it tracked very well. I drained the tank, reinstalled and put in 10 gallons of gas. Nice, 1/2 tank. I drove to the gas station and filled it up. Full tank. Half way across the parking lot it dropped to 2/3. The next day it read full. Commuting all week now, I should have 1/2 tank. It still reads full.

I would recommend not buying a floatless sender. I have to drop the tank again to put in a normal one.

The failed unit I removed had an air gap in the winding to the wiper through about 75% of its movement. The plastic on the winding expanded and it made no contact. Today I got out my meter and the ground side of the winding to the top flange where you hook up your ground wire reads 800000 ohms. It is practically open between the flange and the bar that attaches to it and it should be close to zero. This was a sender that came from CPP with their aluminum tank.

I found this thread while looking for anyone that may have had issues with a floatless sender.

What sucks is I have a bad Dolphin sender in another truck and yet another bad sender in one of my Model A tanks.

Now I wonder who makes a reliable sender. I do not know.

[dsraven]

think of the fuel guage as a needle between 2 electro magnets. one magnet is a steady strength and would pull the needle all the way to one end of the guage if it weren't for the other opposing magnet. the other magnet is a variable strength magnet and it depends on the potentiometer in the tank sending unit for the amount of strength. it makes sense then that either disconnecting the sending unit wire or grounding the sending unit wire would make the guage go all the way to full or all the way to empty. I have a good used sending unit potentiometer in my box of tricks that I use to test gauges with. if that unit makes the guage work properly through the range of movement then the problem would be obviously the in tank unit in question.
make sense?

[wildearp]

I just had a long conversation with Classic Instruments. The old 2012 floatless sender was recalled, 100%. They had calibration and leak issues. They missed mine. They said they are also going to pull the youtube calibration video.

I have a CI mechanical type sender expedited and will install this weekend.

CI will replace mine free with the newer one and also upgrade a second one I have.

The floatless senders are no longer user trimmable. You tell them the tank depth and they send you a specific sender. They also have almost every ohm range that is used in a floatless version.

After checking my original failed mechanical unit, one end of the wiper is ground. It is grounded through the metal shaft of the sender and attaches to the metal flange. Between the shaft and the flange, it measures almost 800000 ohms, practically an open. The failed sender was from CPP and the wiper portion was on plastic which expanded. The wiper misses the center section of the resistor entirely.

[dsraven]

also make sure the tank has a good ground to the body, the body has a good ground to the frame and the frame has a good ground to the battery. you can have all the good positive battery connections you want but if the ground connections are poor then the circuit is incomplete or, at best, poor.

[_Ogre]

Now I wonder who makes a reliable sender.

try finding a speedo for a 55-59 truck
i've gone thru 4 new ones and finally put in an old one that is good enough

i like my nolimit gas tank, but i hate the universal sending unit rob shipped with it

[OrrieG]

Originally Posted by _Ogre

try finding a speedo for a 55-59 truck
i've gone thru 4 new ones and finally put in an old one that is good enough

i like my nolimit gas tank, but i hate the universal sending unit rob shipped with it

Speedos are for wimps. Just go with the flow and watch the tach...

[Coupeguy2001]

It has been my experience that no ground on the sender makes the gauge go full scale, and read full all the time.

If you can't get full scale with full tank, you might have low volts.
The key (ignition) switch may need to be replaced, or you might try piggy-backing the gas gauge wire from another source, and see if a better connection or cleaning the terminal gives you a better reading.

[_Ogre]

Originally Posted by OrrieG

Speedos are for wimps. Just go with the flow

truk likes to be leader of the pack
we are the flow