Can You Adjust the scale on the Fuel Gauge?

[5thhorsemann]

Thats a problem, if you are showing 3/4 full (at full) and 1/4 full at empty you are only using 1/2 the gauge range over 100% of the sender range. Disconnect your gauge at the sender and see what it reads, should show empty. Next jump the gauge leads out at the sender, gauge should read full. this will basically test your gauge for function but not calibration.

[AZ-240z]

On 4/29/2006 at 10:58 AM, AZ-240z said:

Hello Tomohawk,

This is just speculation on my part, but the fuel gage sending unit is no more than a float suspended in the fuel tank. I would take a look at this first, to see if it moves freely, is not binding, or possible leaking fuel into the float, itself.

The float is mounted on the end of a long wire rod, or arm and could possibly be calibrated by bending the arm slightly to adjust the signal in the sender, itself.

I haven't done this, myself, but this might be a possible fix. The tank would have to be drained, then refilled with a known quantity of gas not to exceed the height of the port where the sending unit is mounted, say, a quarter of a tank. Then, remove the sending unit and make incremental adjustments to the arm until the gage reads 1/4.

Again, as a disclaimer, I have not done this, and am just offering an idea which may, or may not, have any merit.

Dan

Well, it's been a while, but I want to revisited this subject with another possible solution to inaccurate fuel gauge readings.

My gauge would read about three needle widths below the full mark after filling the tank (like forever), and would still have a lot of gas remaining when reading well below empty.

I drained my tank of the 2.5 gals remaining and removed the sending unit.  Outside the tank, I hooked up the sender to the wiring harness, grounded the earth wire to the chassis, and turned the ignition key to on.

I then manually moved the sender arm through its full range of movement causing the pickup contact to slide on the resistance windings full scale from empty to full.  The gauge readings remained unchanged as when installed in the tank.

the reasons I narrowed my focus to the sender as the culprit are:

1.  I removed my fuel gage and hooked up another spare gauge.  There was no change in fuel      readings.

2.  The fuel sender sub-harness is new and properly grounded to the chassis.

3.  The sender is NOS, and replaced a NOS sender installed a few years ago with the same issues.

4.  The fuel tank has been restored to as-new condition with all of the correct fittings.

I had previously spoken about possibly "bending" the float arm on the sender to change

the gage reading.  

Well, after taking a closer look at the sender, I  noticed a set screw on the pivot arm of

the sender float arm.  I also noticed that the contact on the sender was not near the top 

of the resistance winding scale when the arm was moved to full tank position.

With nothing to loose, I loosened this set screw and rotated the pickup contact up to

the top of the windings while holding the float arm against the full stop position.

this set screw was then retightened and finger were crossed.

Someone else may have already tried this, but, none the less, I'm feeling pretty

excited about my discovery and anxious to try it out.

Again, outside the tank the sender was wired up and grounded and, with the

ignition switch on, the sender was manually moved to full stop causing the gauge to

move to The full mark for the first time in years.

Looking very promising, I reinstalled the sender and dumped the 2.5 gallons of gas

back into the tank.  I have always thought that, at the empty mark, there was probably

2 to 2.5 gallons of reserve fuel remaining, or maybe I read that somewhere.

Anyway, almost afraid to try it out, I cranked up the engine to see if anything changed.

The fuel gauge worked its way up to the empty mark and stabilized there with 2.5 gallons

of fuel.  Success, at least for now.  I couldn't get to the gas station fast enough to try a 

full tank on my gauge.  When the station pump clicked off automatically signaling a full

tank, I switched the ignition on and the gauge indicator needle slowly moved to and 

stabilized EXACTLY on the full mark.

I am definitely a happy camper right now.

Since I don't drive my car frequently, something that I have to keep in mind is, the gage will

move toward the half full mark more rapidly due to the shape of our gas tanks.  The sender is

mounted in the deeper (fatter) end of the tank.  When the float on the sender arm reaches

the halfway point, there is much more than half a tank of gas left, if that makes sense.  Thereafter,

the gauge needle will move more slowly to be consistent with the actual amount of fuel

 remaining in the tank.

Also, something I failed to mention.  With the sender out of the car, I used a Q-tip with some wax

and grease remover to clean the resistance windings of any gas varnish buildup, and a piece

of 220 sandpaper to burnish the pickup contact for a more positive contact.  Not sure if this

contributed to my success or not.

I hope this may help those with similar issues.

 

Dan

Also, I plagurized a photo of a gas tank from one of siteunseen's posts to

help with the above explanations.

 

 

 

 

 

Edited January 28, 2017 by AZ-240z

[Zup]

Excellent work Dan!

Great that you kept working toward the solution and posted to the old thread to wrap it up with additional information, which will be valued by anyone in the future with a similar issue.

10 hours ago, AZ-240z said:

I don't drive my car frequently

You need to fix this immediately though!! 

 

 

[AZ-240z]

Thanks, Jim D.

Sharing our all-too-infrequent successes is what this society of originalists is all about for me.

As far as actually driving my car, I'm afraid a severe case of paranoia and OCD controls my 

Z driving habits these days.  I do take it out on weekends though for a 60 mile tour of 

Phoenix freeways when they are pretty quiet to renew the spirits and keeps things in good 

operating condition.

Dan

 

 

[wheee!]

Before and after soaking in CLR. I will check the adjustment screw but I was getting a pretty good reading on the ohmmeter when I cleaned it last fall.