dusterglenn
Well-Known Member
I'm 99% sure my gauge is the source of my problems. But before I buy a replacement, is there a way to test the calibration of a factory fuel gauge?
Testing Fuel Gauge?
- Thread starter dusterglenn
- Start date
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Factory settings 73 ohms = empty. 9.6 ohms minimum = full
dusterglenn
Well-Known Member
Yes, I tested the sender, and it measures 78 ohms empty, and 11 ohms full. I also rigged up the sender out of the tank to see how the old gauge read with the sender arm at various points. With the arm at full, the gauge read just under 3/4. With the arm at 3/4 or below, the gauge read just over empty. The needle also floated around with each 'pulse' from the limiter.
What I'd like to know is, before I install a "good used gauge", can I bench test it?
What I'd like to know is, before I install a "good used gauge", can I bench test it?
Sounds like you did bench test it with a "known good" sender. A more precise test/calibrate is done with a decade resistance stack.
dusterglenn
Well-Known Member
Well, I'm completely stumped. I confirmed my resistance reading on my sending unit. Not dead-on to the spec, but within 3-4 ohms at either end of the scale. No dead spots throughout the range either. I changed gauges, and get exactly the same reading on either one. I got exactly the same reading as in my last post.
So I hooked up my test light to see if there was a regular pulse. With the test light grounded to the body, and the probe in the connector at the kickpanel, the gauge steadied out. With the float arm at empty, the gauge read a quarter, with the arm at full, it read 3/4. What the heck is going on here?
So I hooked up my test light to see if there was a regular pulse. With the test light grounded to the body, and the probe in the connector at the kickpanel, the gauge steadied out. With the float arm at empty, the gauge read a quarter, with the arm at full, it read 3/4. What the heck is going on here?
Sounds like the bi metal responder inside the gauge is done.
It starts life straight as an arrow and bends with temperature change which moves the needle. I suspect yours now has a slight bend at room temperature which means its lost its temper.
One other condition is crud build up on the nichrome winding to the point it is restraining the bi-metals' movement.
Nothing lasts forever.
It starts life straight as an arrow and bends with temperature change which moves the needle. I suspect yours now has a slight bend at room temperature which means its lost its temper.
One other condition is crud build up on the nichrome winding to the point it is restraining the bi-metals' movement.
Nothing lasts forever.
dusterglenn
Well-Known Member
My only concern is that both gauges that I tried read exactly the same. I just don't like coincidences. Oh well, I guess there's an aftermarket fuel gauge in my future.
Woah , back the truck up here. Within 3 or 4 ohms is not calibrating or passing tests. There's your problem.
How to test... set a multimeter on ohms. Put the leads together, Some meters will self adjust zero ohms. Others will display zero brriefly then display ohms resistamce in itself/leads.
Example; my meter has 1.5 ohms resistance in its leads.
When testing a fuel sender I expect tgo 74.5 ohms at empty ,which is a true 73. note that 78, 87, 200, anything higher than 73 is also empty.
Full doesn't work the same. 9.6 ohms is the factory spec for full. I expect to see 11.1 on my meter.A true 11.1( 12.6 my meter ) will not get a full gauge report.
Facts ; A true 10 ohms will get on the full hash mark. Anything less than true 9,0 ohms will overheat the gauge.
How to test... set a multimeter on ohms. Put the leads together, Some meters will self adjust zero ohms. Others will display zero brriefly then display ohms resistamce in itself/leads.
Example; my meter has 1.5 ohms resistance in its leads.
When testing a fuel sender I expect tgo 74.5 ohms at empty ,which is a true 73. note that 78, 87, 200, anything higher than 73 is also empty.
Full doesn't work the same. 9.6 ohms is the factory spec for full. I expect to see 11.1 on my meter.A true 11.1( 12.6 my meter ) will not get a full gauge report.
Facts ; A true 10 ohms will get on the full hash mark. Anything less than true 9,0 ohms will overheat the gauge.
I found a post, someone checked their old Miller sender test tool:
Just checked the Miller C-3826 gauge checking tool and it's ------
L = 73.7 Ohms
M = 23.0 Ohms
H = 10.2 Ohms
Seems to me your sender is doing it's job What about the instrument limiter? How do you know it's OK? I think I'd be supplying an artificial 5V test voltage, or did I misunderstand?
Also, you checking at static 12V battery voltage, or "charging" voltage? I'd think that may make some difference.
As Red noted, be very careful at low ohms readings about not only test lead resistance, but your connections. It doesn't take much of a poor probe connection to throw you off an ohm or 3
My fluke has a special "low resistance" scale and a menu which nulls out the lead resistance, which helps.
Just checked the Miller C-3826 gauge checking tool and it's ------
L = 73.7 Ohms
M = 23.0 Ohms
H = 10.2 Ohms
Seems to me your sender is doing it's job What about the instrument limiter? How do you know it's OK? I think I'd be supplying an artificial 5V test voltage, or did I misunderstand?
Also, you checking at static 12V battery voltage, or "charging" voltage? I'd think that may make some difference.
As Red noted, be very careful at low ohms readings about not only test lead resistance, but your connections. It doesn't take much of a poor probe connection to throw you off an ohm or 3
My fluke has a special "low resistance" scale and a menu which nulls out the lead resistance, which helps.
dusterglenn
Well-Known Member
I went back and checked the notes I scribbled down when I tested the sender. 78 ohms empty, 11 ohms full. (3-4 ohms was a guess, I should have re-read my old post.)
I do get a steady regular pulse from the voltage limiter, but I haven't confirmed 5v output, bad assumption on my part. Battery voltage it 12.5v, but the car is not currently running.
Is there an easy way to test a voltage limiter? I have at least 3 of them in my toolbox.
I just thought of this, could a bad body to engine ground be the cause of this problem?
I do get a steady regular pulse from the voltage limiter, but I haven't confirmed 5v output, bad assumption on my part. Battery voltage it 12.5v, but the car is not currently running.
Is there an easy way to test a voltage limiter? I have at least 3 of them in my toolbox.
I just thought of this, could a bad body to engine ground be the cause of this problem?
I dont know a way to test the mechanical limiter.
Lets examine the ground path... first there is a jink clipped on the fuel lines at the sender. Then there are X number of fasteners holding the fuel line to the chassis. Then there is another link between the chassis and the engine block at the firewall. Finally the ground wire between the engine block and battery post. Plenty of places for resistance to accumulate between the sender and the battery. resistance in most of these places would effect all of the vehicles electrical rather than the fuel sender alone.
Lets examine the ground path... first there is a jink clipped on the fuel lines at the sender. Then there are X number of fasteners holding the fuel line to the chassis. Then there is another link between the chassis and the engine block at the firewall. Finally the ground wire between the engine block and battery post. Plenty of places for resistance to accumulate between the sender and the battery. resistance in most of these places would effect all of the vehicles electrical rather than the fuel sender alone.
dusterglenn
Well-Known Member
In an effort to err on the side of caution, I've also soldered a ground wire to the sending unit that bolts to the body/floorpan. And a ground wire from the cluster to one of the steering column mounting studs.
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