Fuel Level Sender/Fuel Gauge Schematic? (Page 2/2)
pmbrunelle JUN 24, 11:18 AM
Gold is not recommended for mating with tin. Refer to the Tin Commandments. But I haven't heard of problems with zinc-plated hardware.

The uninformed consensus of my work colleagues and I is that Pb-free HASL is a good choice for screw-contacts with a PCB.
Chris Eddy JUN 24, 02:06 PM
I worked up a small board, single sided (traces cannot touch the metal meter housing), HASL (hot air solder leveling, tin-lead), where the 3W resistor leads lay down and solder on the surface of two pads.. (since leads cannot go through hole). It is not fully a rectangle, there is an ear on the upper left and lower right where the resistor pads solder (the body of the resistor is at an angle in the center). I will use a countersink to open up the holes in the bottom of the board slightly so that it slips over the nylon sleeves protruding through the meter housing.
I like zinc plated 6-32 hex nuts with the built in washer, the original steel spring nuts rust and are part of the problem, and are too large in diameter anyhow.
These bare boards will probably be in the ~50 cents range, so the resistor and shipping will cost far more when making them.
I will order with the next group of boards soon.. along with the next version of the instrument back panel circuit board.
theogre JUN 24, 03:17 PM
Ω in my 1st post was measured w/ a very old Fluke 77 and good probes....

Today I put the probes shorted get 0.3Ω

Took my new Craftsman Pro "Industrial" Model 82003 w/ REL and w/o tare get 0 to 0.4
put Fuke probes get 0 - 0.2, After Tare 0 - 0.1 (Auto range on.)
FG Pink resistor is 83.3Ω on this meter.
Temp resistor is 94Ω Seems Lite Green or Green Blue color.

Test again w/ new probes get so close to same doesn't mater.

The 87 and 86 I have are both the same resistance for both gauges.
OP has same pink resistor. One handy measure 84.7Ω

Very possible other batches of gauges have different resistor to "tune" the batch. Maybe that's why GM doesn't mention the resistors anywhere available to the dealers or the public.
If true you can't simply use same resistor on all of the gauges for whatever job and think will be better, likely will be worse.

FG resistor getting hot, more so w/ tank empty, means can't use "standard" pots unless you like "magic smoke." Most pots of all types handles < ¼ watt.
Temp sender likely never sees close to 0Ω but Fuel and OP senders operates 0 - 90Ω all the time.

Yes, OE resistor is "countersunk" on meter side to clear plastic insulation and so the nuts hold the resistor and the coil inside tight to bottom of the back shell. W/o the resistor and nuts, Coils can move if you push the bolt in w/ little effort. EVEN IF you use 4 nuts, still needs "fiber" washers under to keep coils in place.
OP resistor is same but weird nuts under them to make contact w/ tach board. Likely oversize the PC holes to clear coil insulation. (Not taking weird nut off.)
Chris Eddy JUN 25, 06:23 PM
I did some experiments with a fuel gauge.
I apologize, I am not great with whipping up graphics, which would be perfect here.
There are three terminals on the fuel gauge, and inside are two coils.
There are pictures on line showing this type of gauge on other vehicles.
The coils are in series.
The 12V connection is on the CCW (right) terminal viewed from back.
The GND terminal is on the 6 oclock position.
The gauge sender (0-90 ohms) terminal is on the CW (left) terminal.
The ignition voltage goes to the 12 terminal, and there is a coil (coil 1) connected to the gauge sender terminal. It measures 86.7 ohms.
There is another coil (coil 2) from the gauge sender terminal to the gnd terminal. It measures 102.8 ohms.
The gauge sender of course connects to ground.
The ceramic resistor, a yellow one measuring 88.1 ohms in my case, is in parallel with coil 1.
Connecting resistors from the gauge sender terminal to ground gives us a moving needle.
I cannot make every R value, but the 3 values that I have (plus 0 ohms) give realistic readings.
I can remove the ceramic resistor and replace it with another dummy resistor, in increments of 10 ohms.
When you change the ceramic resistor value, it clearly changes the span, not the zero. It has greater effect at the top, and almost none at the bottom.
At the top, a 10 ohm change in value yields about a 1/8 tank change in indication.
Raising the resistor value bumps the needle down.
Lowering the resistor value bumps the needle up.
With this info, and a gauge that is not damaged, one should be able to change the ceramic value until their gauge is calibrated.
You might even be able to make it so that a full tank is actually on the full mark, not above it.
This assumes that the tank sender is 0-90 ohms, which of course is not exact.
I will make up a test device with resistors that allow you to connect to empty, 1/4, 1/2, 3/4, and full terminals for testing and calibrating gauges.
theogre JUN 25, 09:53 PM
As look from back...
FG pins are:
1. left insulated pin to sender
2. bottom non-ins pin to ground
3. right insulated pin to "12v"

I get: (new meter w/ REL used)
1 - 2 100Ω
1 - 3 85Ω
2 - 3 185Ω just to see others match actual Ω across 2 coils.

Pink Resistor is between 1 and 3 pins. Can say is is voltage divider w/ the sender, soft short to one coil, or whatever.

Tank sender is "0 - 90Ω" but isn't made very accurate. Tank "full" should = sender at 90Ω but often the "pot" have extra space.
Many cars Gauges Empty is a bit above Tank Empty w/ E-pumps but not all. W/ "old" mechanical FP many cars had then Very close or at = . Old carb cars gauge said empty you aren't driving more then maybe 1 or 2 blocks.

IOW Can reach full or more is enough to many... Is a Bigger Problems when a gauge sticks or otherwise doesn't read last ~ ⅓ of tank.

Adjusting "full..."
Ideally... Gauge Full is ~ = Tank Full IF you stop filling when Nozzle shuts off the First Time.

But that's making several assumptions by the maker... Many Problems, some main ones:
Nozzles that work properly. Many don't.
For Fiero... Make to work w/ Common Nozzles in 70's to early 90's. Most to All back then wasn't "Vapor Recovery" and other types that still causes problems for even New cars many times. (Most Station Pumps drops plastic bellows on the nozzles now but most are still VR systems.)
Many Nozzles even back in 80's didn't quit fit the Fill Port on many cars. This cause the auto shutoff to trip often trip a lot w/ some cars. Other cars would late auto shutoff and cause spillage.
Some stations have "high speed" pumps. This often have problems when you pull the handle all the way on. Fill at lower speeds, only pull handle to middle max.
Many people "stuff the tank" and to the point even spill fuel trying to force last few drops. This causes way more problems then just a gauge reading over full.

Above are why you often see a gauge past "Full." But Ignore Many cars w/ Gauges w/ hard limits in them or BCM controlling gauges that may never register overfilling fuel tank. Most of those just stay at Full mark often for hours to days depending how much you drive.

If you "calibrate" any gauge then have you fix everything like clean up dash back board and gauge clips. Even then the calibration may not last long.

Side note: In many places, some of above reasons are why local fire codes and State "EPA" require nozzles that won't lock to disable auto fill. Many idiots "bypass" that and often spill more fuel at minimum. In many places, anyone "bypass" non locking nozzle can be ticketed etc. Many station can/will remotely shut down a transaction seeing pump flowing w/o you touching or move away because Station can get fined by Code, "EPA" or Fire Marshal offices if they ignore this.

[This message has been edited by theogre (edited 06-25-2020).]