Author Topic: Fuel gauge problems  (Read 103 times)

djustice

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Fuel gauge problems
« on: July 11, 2019, 02:33:09 AM »
It all began when i switched fuel tanks to a hyperfuel efi gas tank, droped the old tank, installed new tank with new pump and new sender.
Everything worked, but i struggeled with indexing the fuellevel sender, resulting in a flipped rehostat (0-90 Ohms) is now 90-0 Ohms.
So my fuel gauge reads backwards.
To save me the hassel of renting a garage spot dropping the tank and getting soaked in gasoline (again!) i opted for a speedhut programmable fuel gauge where i can set any resistence i wanted.
I took the dash apart, and removed the fuel gauge, located the tan wire from instrument harness plug that comes from the fuel level sender and hooked it up, and grounded the the other wire to the instrument panel gauge pod mounting bolt.



fired up the car and sett pre set 90-0 ohms, and voila! the gauge read a little under 1/2 tank what i expected. drove to the gas station and fill it almost full (there is a warning with tanks inc that you should never fill the gas tank all the way full)

Now the new fuel gauge slowly began to make it's way towards full, it went above 3/4 and then suddenly it went all the way back to 0 and have stayed there ever since.
I have tore out the dash multiple times and am getting a bit fustrated, in testing i have found the gauge responds to what seems the correct level by joining resitance wire from sending unit with ground from sending unit and +12v wire, but this does not seem rigth according to instructions.



If the gauge would have read full all the time it should be a sending unit ground problem, if it reads empty all the time the resitance wire from sending unit should be grounded out. but i dont belive in such a coincidence that i be getting this problem 5 minutes after installing a new gauge.

If it is grounding out i will have to drop the tank because it runs on top of the tank and back to the tail end.

New gauge: https://www.speedhut.com/gauge/GR-FUELLEV-01/1/Fuel-Level-Gauge-(programmable)-(w--warning)
Tanks inc sending unit: http://www.tanksinc.com/index.cfm/page/ptype=product/product_id=276/category_id=184/mode=prod/prd276.htm
« Last Edit: July 11, 2019, 12:13:31 PM by djustice »
1973 Firebird formula 400 W/YC code 455 (73 casting)
6x-8 heads, hyperfuel efi gastank, scorpion 1.5 Roller rockers, holley sniper efi, edelbrock performer inntake, Headman 28150 headers 1 3/4" primary, Pypes SGF11R exhaust, cam unknown, alu radiator w/twin 12" fans. Yukon duragrip posi w/3.42 gears.

firebirdparts

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Re: Fuel gauge problems
« Reply #1 on: July 11, 2019, 06:48:50 AM »
I did not see the instructions for the gauge right off.  The sender is a variable resistor.  So the two wires on the sender, the gauge needs to measure that resistance, so it needs to connect across those two terminals.  The factory of course used the body of the car for one of the conductors, like they do everything, so the factory gauge it looked like only one wire there.  The second circuit is unseen.

I need to find the gauge instructions to comment any more.  Do you have this installed in the center of the main cluster, with a factory printed circuit?
I want to be like Paul Kenny when I grow up
Joe Bays
1977 Y82 4-speed (red interior)
1978 Skybird 350
1978 Redbird 305
1979 Redbird 301 4-speed
1992 Lincoln Mark VII LSC/SE (red)
1970 Datsun Pickup
1953 Chevy pickup (converted 4x4)
1988 T-bird Turbo Coupe

djustice

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Re: Fuel gauge problems
« Reply #2 on: July 11, 2019, 07:15:02 AM »
Thank you for the reply Firebird parts, ill try to link the download link for instructions below
https://www.speedhut.com/instructions/2in_and_258in_rev_fuel_level_instructions.pdf

Yes i have removed the fuel gauge from the instrument pod, so that the middle part of the PCB is now floating and is unsuoprted only left and rigth side is supported with bolts and ligthbulbs.

New gauge is mounted trough lens and faceplate (drilled a 52 mm hole trough both)
« Last Edit: July 11, 2019, 07:21:23 AM by djustice »
1973 Firebird formula 400 W/YC code 455 (73 casting)
6x-8 heads, hyperfuel efi gastank, scorpion 1.5 Roller rockers, holley sniper efi, edelbrock performer inntake, Headman 28150 headers 1 3/4" primary, Pypes SGF11R exhaust, cam unknown, alu radiator w/twin 12" fans. Yukon duragrip posi w/3.42 gears.

djustice

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Re: Fuel gauge problems
« Reply #3 on: July 11, 2019, 12:12:52 PM »

in testing i have found the gauge responds to what seems the correct level by joining resitance wire from sending unit with ground from sending unit and +12v wire, but this does not seem rigth according to instructions.


disregard this part, the gauge wil float to full when combing both leads from the gauge, just desperate trouble shooting.

And i found out PCB will be hot smokey and toasted in a matter of 1-2 seconds if you mess around with a positive wire where it should not be!
1973 Firebird formula 400 W/YC code 455 (73 casting)
6x-8 heads, hyperfuel efi gastank, scorpion 1.5 Roller rockers, holley sniper efi, edelbrock performer inntake, Headman 28150 headers 1 3/4" primary, Pypes SGF11R exhaust, cam unknown, alu radiator w/twin 12" fans. Yukon duragrip posi w/3.42 gears.

firebirdparts

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Re: Fuel gauge problems
« Reply #4 on: July 11, 2019, 02:15:18 PM »
Well, that gauge is pretty simple.  Which calibration are you using?
I want to be like Paul Kenny when I grow up
Joe Bays
1977 Y82 4-speed (red interior)
1978 Skybird 350
1978 Redbird 305
1979 Redbird 301 4-speed
1992 Lincoln Mark VII LSC/SE (red)
1970 Datsun Pickup
1953 Chevy pickup (converted 4x4)
1988 T-bird Turbo Coupe

Re: Fuel gauge problems
« Reply #4 on: July 11, 2019, 02:15:18 PM »

djustice

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Re: Fuel gauge problems
« Reply #5 on: July 11, 2019, 02:40:41 PM »
I am using 90-0 Ohms (3/4 mark) i did som testing with an ohm meter , i probed the brown/tan wire with one lead, and used the other lead to ground and get no reaction from the ohm meter (i did cross both leads of the ohm meter together just to make sure it works and got 0002 ohms so it works).  this worries me as it seems the tan wire got infinite resistance , i went to the trunk and unplugged the connector from the fuel level sender (same tan/brown wire) and pobed the wire and to chassi ground, same result no reading, so i guess the wire between the gastank and trunk floor migth have grounded out or i have some how burned my rehostat in the tank. On saturday i get to borrow a garage, ill be jacking up the rear of the car and lowering the gastank alittle, it will still be hanging by the straps, but enough to get a look at the sender connectors and and ohming directly to sender and ground terminal on the fuel level sending unit.
1973 Firebird formula 400 W/YC code 455 (73 casting)
6x-8 heads, hyperfuel efi gastank, scorpion 1.5 Roller rockers, holley sniper efi, edelbrock performer inntake, Headman 28150 headers 1 3/4" primary, Pypes SGF11R exhaust, cam unknown, alu radiator w/twin 12" fans. Yukon duragrip posi w/3.42 gears.

djustice

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Re: Fuel gauge problems
« Reply #6 on: July 12, 2019, 11:52:00 AM »
Update: borrowed an advanced multimeter that selects ohm range automatically, probed the brown/tan wire running to tank sender (rehostat) At the trunk and probed it to ground, it showed 180 Kilo ohms :(  i also  unclipped the the sender wire from trunk and and hooked the ohm meter again, in the dash end of the wire i grounded it with an aligator clip to instrument bezezl ground. it showed about 10-12 ohms, so the sender wire from trunk to dash seems good.
but trunk to sending unit seems possibly grounded , og the new sendingunit is toast.

Just to exclude the new gauge i connected the old sending unit (lockring type) to sending post and ground tab while moving the float, and the gauge responded.

so.... possibly drop the tank Again sigh....  rigth now i am tempted to take an anglegrinder to the trunk floor and make a permanent acsess panel.
« Last Edit: July 12, 2019, 11:54:49 AM by djustice »
1973 Firebird formula 400 W/YC code 455 (73 casting)
6x-8 heads, hyperfuel efi gastank, scorpion 1.5 Roller rockers, holley sniper efi, edelbrock performer inntake, Headman 28150 headers 1 3/4" primary, Pypes SGF11R exhaust, cam unknown, alu radiator w/twin 12" fans. Yukon duragrip posi w/3.42 gears.

firebirdparts

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Re: Fuel gauge problems
« Reply #7 on: July 15, 2019, 11:54:58 AM »
I wondered about that.  There are two circuits to the sender, and one of them can be grounded and you shouldn't have a problem with that.  But the other one needs to be isolated.
I want to be like Paul Kenny when I grow up
Joe Bays
1977 Y82 4-speed (red interior)
1978 Skybird 350
1978 Redbird 305
1979 Redbird 301 4-speed
1992 Lincoln Mark VII LSC/SE (red)
1970 Datsun Pickup
1953 Chevy pickup (converted 4x4)
1988 T-bird Turbo Coupe

djustice

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Re: Fuel gauge problems
« Reply #8 on: July 15, 2019, 02:19:09 PM »
IT migth possibly be grounded somehow,but i have had the tank with current sender in since may and it worked al this time albeit in reverse. But there is also a chance the wire touched a +12V lead while testing, i just hooked the wire up loosley to the sendingwire in the dash and pushed the whole assmbley loosley in while testing. Drove to the gas station about 2 miles away and back for a fill up to check gauge response, i suspect it touched a positive lead and burned up the rehostat.

Today i contacted a local boat service center, and asked if they had a 6" 5 hole sender, and they had one in stock, so i bought it.

Like this:
this one is made of stainless steel, no more clocking the rehostat and floatside to clear the baffling, less things to go wrong.
So i unhooked the trunk sending wire coupled the the new S5 unit and grounded it the trunk latch, progammed the gauge for new ohm scale, and boom! worked flawless. no i need to get my battery pack anglegrinder back and i should be in businness.
1973 Firebird formula 400 W/YC code 455 (73 casting)
6x-8 heads, hyperfuel efi gastank, scorpion 1.5 Roller rockers, holley sniper efi, edelbrock performer inntake, Headman 28150 headers 1 3/4" primary, Pypes SGF11R exhaust, cam unknown, alu radiator w/twin 12" fans. Yukon duragrip posi w/3.42 gears.

Re: Fuel gauge problems
« Reply #8 on: July 15, 2019, 02:19:09 PM »
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