Gas Gauge Question (wrong forum?)

City
Atlanta
State
GA
#1
So here is one that I just can't figure out. My fuel gauge reads full when full, goes down at what appears a normal rate but when I am on empty and go to fill my 15 gal tank I get 10 gallons in at most. I thought it was my sending unit and figures what the hell, it is better than thinking I have more gas than I do so I stop more often but I never run out of gas. Well, last week I put in one of the new Holly intank fuel pumps and sending unit combinations. I have fuel injection and needed a new pump. I thought, this will definitely solve the gauge problem, but its acting just about the same. Has anyone experienced anything like this? Could it be the actual gauge in the dash? Seems weird to me that two sending units act the same and I am positive I have a 15 gal tank not a 20 gal tank with the wrong sending unit. Any thoughts are appreciated.
 

AJ2393

Scrambled in the Head
LIFETIME
CJ-8.com Member
City
Westport
State
MA
#2
Has the float been adjusted properly in the tank? I don't think I have ever seen one work correctly out of the box.
 
City
Atlanta
State
GA
#3
Has the float been adjusted properly in the tank? I don't think I have ever seen one work correctly out of the box.
The sending unit / fuel pump I am now using isn't adjustable and "the module includes a pre-calibrated fuel-level sending unit that was designed to work with the factory fuel gauge already in your vehicle". I bought the Holly 12-307 fuel pump / sending unit all in one. It is working great and I thought I was killing two problems, inaccurate fuel gauge and overheating fuel pumps, with this. The fuel pump works great but I just think it is weird that the gauge is doing almost exactly the same thing with both sending units. That is why I was asking about the gauge in the speedo cluster, that is the only part that has not be changed multiple times. Here is a link to the fuel pump I put in, it is working really well with the MOPAR fuel injection kit for the 4.2.

https://www.holley.com/products/fue...uel_pumps/muscle_car_efi_modules/parts/12-307
 

Spieg

Scrambler Junkie
LIFETIME
CJ-8.com Member
City
Aurora
State
CO
#4
It looks like the float arm could be adjusted just the same as the original (although they state it is precalibrated, so should not need adjustment).
 

Belizeit

CJ-8 Member
CJ-8.com Member
City
River Ridge
State
La
#7
Mine is not accurate, probably rusty, but could try adjusting the float as Spieg noted.
 

FLCJ8

Legacy Registered User
City
Palm Bay
State
FL
#8
Any thoughts are appreciated.
You could check the resistance of the sending units based on these specs:
sending unit.PNG
Because they both are acting the same, chances are it's related to the gauge.
The resistance (ohm) readings for the factory gauge are:
gauge.PNG
 

wm69

Scrambler Junkie
LIFETIME
CJ-8.com Member
City
God's Country
State
AR
#10
So here is one that I just can't figure out. My fuel gauge reads full when full, goes down at what appears a normal rate but when I am on empty and go to fill my 15 gal tank I get 10 gallons in at most. I thought it was my sending unit and figures what the hell, it is better than thinking I have more gas than I do so I stop more often but I never run out of gas. Well, last week I put in one of the new Holly intank fuel pumps and sending unit combinations. I have fuel injection and needed a new pump. I thought, this will definitely solve the gauge problem, but its acting just about the same. Has anyone experienced anything like this? Could it be the actual gauge in the dash? Seems weird to me that two sending units act the same and I am positive I have a 15 gal tank not a 20 gal tank with the wrong sending unit. Any thoughts are appreciated.
I had the exact same symptoms on my green CJ7 with the 20 gal tank, even down to the 10 gallons left when the gauge gets to E. I've always assumed it was the sending unit, and have a replacement on the shelf to go in at some point. Not too long ago the gas gauge went totally dead, so I'm watching this with interest. Would be nice if I didn't have to drop my tank, although replacement sending units are probably easier to find that good OEM gas gauges.
 
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