Technical Need A Cooler Mind (Fuel Gauge Issues)

!957 Chevy 210 has had fuel gauge reading issues since purchased. Never would read Full after tank being completely filled.

Today I pulled the sender (a new unit installed by previous owner) and bench tested to a spare 1956 dash cluster. Result was that sender wouldn't send needle over to full like when in the 57. Next I bench tested old original sender that was boxed and came with the car in the trunk. It's sweep would make the 56 cluster go to full no issue at all. Awesome I think to my self. So then I wire it out side of the tank for a test. No good same issue, it'll only sweep 5/8 of the way from empty.

Next I test both sender with a multimeter and old unit actually has good readings compared to the new one which I expected. Next I send full ground to sender wire and gauge read empty then removed ground and gauge read full. This as I've read tells me if gauge is working. But how well is this type of testing?

So now I'm lost until I look closer under the dash for wiring issues. But that will wait until later since I'm frustrated.

Is it possible that the gas gauge is at fault here even though I got it to read E and F by grounding sender wire then removing ground at sender wire at the back of the car? Or am I so frustrated that I'm not listening to myself where the bench test worked with the old sender? Bottom line, I hate to buy a gauge and be wrong.

 

Bad ground between tank and frame.

 

Has extra grounding in place.

 

I had a similar issue, I found bad / weak ground @ instrument panel & gauge stud on inside, ( face & backing ) " Not back side where connection from wire harness connects.


Also I do not know or if matters ,don't those gauges have copper winding in between face & backing ? If so maybe not the same amount of resistance between the gauge in the car 57 compared to the 56 one you're bench testing?

 

Tech Tip-fuel gauge from Ol 55 East Coast Chevy
https://www.eastcoastchevy.com/X6tech/tech_gas.html

 

@Johnny Gee
I had a similar issue
On a 57 Chevy [which other people have tinkered with in the past] check to see if there is 1/4 increments on the actual fuel gauge.


On this ^^^^ when we purchased it, a previous owner had swapped the fuel gauge for the Temp gauge [Temp gauges don't have 1/4 increments]
They can easily be swapped behind the printed lenses.

Check to see if the correct wire is the 12v+ and sender wire [They are Tan and Brown and easily mixed up]

Also buy a potentiometer from an electronics store. Use this as a substitute sender to test the range of the gauge.

One last thing which is so simple ....... Check to see if the needle isn't bent and rubbing the face or the lense

 

Hello,

We had similar problems on our fuel gauge. I could not find a reason for it despite my best efforts. So, I called an auto/boat electrician repair person. He came over, ran several checks with his equipment and in 30 minutes, he had reached a conclusion. A faulty fuse. The fuse looked good, no breaks in the wire, crinks where they should not be, and no cracks in the glass , but he replaced it with a new one.

"Wa---lah..." the fuel gauge read full when it was full, not half empty.

Jnaki

It seemed simple enough, but it was hard crawling around under the dash, upside down and feet dangling outside. So, the electrician was limber enough to do the flexible checking of the wires and found the culprit. Despite our abilities, sometimes it takes an outside eye and their perspective on the problem. YRMV

 

This doesn't exactly apply but on my 64 El Camino when I first got it it would never go to full. Turns out there's two screws holding the face of the gauge and one was missing and the full side of the gauge had shifted and was lowered so it would only read 3/4 of a tank. Once I pulled the gauge out and found the missing screw everything worked great.

 

Take a look inside the tank with a flashlight or one of those snake light camera things in the fuel sender hole for some baffle or other obstruction that would interfere with the swing of the sending unit.

 

That my next step. It's just a pain because of how deep that cluster is plus the amount of work to remove the cluster. That's really why I'm upset. I know of the rch wire your referring to as I've had that issue on a different vehicle.

Now that's in your face funny but not the case here.

The observation of both senders at the gauge was done outside of the tank.

 

Hmmmm, I am interested in what you find because just out of nowhere my 57 fuel gauge reads empty most of the time. Then for no reason at all it will bounce up to what I believe is the correct level. Probably a ground in my case. But as stated above, lots of tedious work to get things pulled apart, ugggh!!

 

That one is most likely the tiny grounding wire in the gauge. The one I had issue with in the past got corrected by tightening the terminal nut's at the back of the gauge. That tiny wire get's contact (sandwiched) via the nut's. That's best case though.

 

Thanks bro and good luck with yours

 

Make sure the float in the tank moves thru it's whole travel..

 

^^^^^ Did

 

Initial Electrical test of gauge - good, it has capability of full travel. Haven't tested partial power yet

What's output signal voltage of the sender from empty to full ?

The output of the sender has to have enough signal / voltage etc to send the gauge thru its full sweep.

Can you find output voltage of the sender at full, empty, 1/2, then apply that voltage to the gauge from a bench tester, see if the gauge reacts as it should. Basically mimic the output of the sender from a bench tester.

If the gauge performs as expected at same voltage as sender - from a bench tester source. Then there's a wiring issue between the gauge and sender

If the gauge doesn't perform as expected, either the gauge has an issue or the voltage from sender is not matched to the gauge range

 

. MN, I feel your pain, my gas gauge does the opposite. Says over full when full, empty at 1/4 tank. But pulling the whole dash off to mess with it? Pass. If it totally dies or something I'll worry about it, but too much work for something that doesn't stop me from cruisin...

Good luck with yours!

 

bought a cheep gauge and sender that was adjustable depth and length kept adjusting could not get it right finally checked it with a multi meter and found it didn,t matter how much I adjusted it readings were not right even out of the tank .had to open up the hole that the float arm came out of to get the right Ohms to go to empty. since then have checked every fuel sender before installation . and have threw away 2 new ones that were no good only saving the float. GM should be the 0.0 OHM empty

 

Just finished pulling cluster from the car. PITA!!!!! by the way. It's a production line friendly design but not repair friendly.

Good point that you have brought up but I wouldn't exactly call it output signal "voltage". I will be testing to see how well sender wire from the back of the car to the gauge for continuity level. There is one other bulk connection in the left kick panel area for all wiring going to the rear of the car from the dash. Is there an issue there?

Stay tuned. Done for the day. Getting warmer and mosquitoes are back in town.

 

I'm with ya, voltage / signal / I dont recall the sender to gauge measurement. Been 20 years since I tested one.

 

0-30 ohm sender is what I'm working with.

 

On a 57 Chevy there is no fuse between the battery and the gauge.

The oil light, temp gauge , gen light, fuel gauge all receive 12v via a tan colored wire connected to the back of the ignition switch
[it is pretty simple "caveman" wiring]

Gauges are pretty simple......They are a couple of electromagnets so not much can go wrong with them. [1 electromagnet is gounded through the instrument panel and the other electromagnet is grounded via the sender]
Even reversing polarity at the terminals won't damage them [they simply don't work correctly]

They can benefit from a couple of drops of "watchmakers oil" on the needle shaft.
I have re-soldered broken electromagnet coil wires on these before [you need good eyesight even when using a magnifying lens]

@Johnny Gee
With the instrument panel lose [but still in place] reach behind and unplug the brown sender wire.
Then connect a jumper wire with a potentiometer in-series to ground [to this post]

you should be able to dial up/down the full range with a potentiometer.
If there is issues still check for 12v at the gauge, and check the instrument panel is grounded.
Also ground the sender wire at the tank, and check for continuity while it is still unplugged

The last gauge I repaired [on a 57] had a bent needle that was catching in one spot.

 

I thought there were no mosquitoes in California. In Indiana that is our state bird.

 

Lol...I came from Manitoba. The mosquitos there have numbers on their wings to aid identification. Especially helpful for tracking after they fly off with your dog!

 

Small update. Wired up 57's cluster this morning on the work bench and both sender's are showing the same sweeping action as when cluster was in the car. That's one way of ruling out vehicles sending wire continuity and good grounding all around.

Later in the day I'll run the 57's senders thru the 56 in my avatar (it has Auto Meter 0-30 gauge) to see how they read vs spare 56 stock cluster gauge I tried before on the bench.

 

At this point the gauge reads 92 ohm's of resistance at both terminals but can not find if that means anything other than it's a 90 ohm unit.

So not knowing how to test a fuel gauge by it's self I did some reading on how to test a fuel gauge and I had to laugh.

Chevrolet shop manual reads- "If KMO-204 gas gauge tester is not available a tester may readily be made by obtaining a tank unit from parts stock".

Now I feel as if shop manuals were talking to me from the book shelf.

 

Here's how to do a fuel gauge range check. The bigger the knob on the pot the easier it is to get an accurate reading. Enjoy them mussels

 

I'm working with all factory matching components. No need to find out what sender I need. But I do see how with some readings an issue would be found. But since both senders ohm out correctly no need to run to electronic store.

 

With temps down outside and mosquito spray on this time here's a late afternoon report.

This time using my 56 in the avatar as a 2nd test mule fuel gauge has shown that both the original sender and replacement sender from the 57 are working fine.

Time for another fuel gauge.