gas gauge problem
Thread Starter
|
Elder User
Joined: Jul 2011
Posts: 609
Likes: 1
From: Stockholm, NJ
gas gauge problem
So LMC sent me my new 38-gal tank and all went fine with install except I still have no reading on my gas gauge. The gauge worked when the sending unit was in the old tank and also worked after my buddy soldered on the extended pickup. To make sure it was getting power, I put a test light into the connector where the sending unit pigtail connects to and my test light was blinking. Not a full constant light. I then disconnected the big wiring clip under the hood and sure enough, when I tested two of the pins, they were blinking as well. The attached photos show where I am getting the blinking test light readings.
Is this normal? If yes, then I have to guess the problem is with my sending unit, but if it is not normal and I should have a constant 12V going back to the fuel tank, and it is blinking where it comes out of the dash harness, and suggestions on my next step?
Thanks
Frank
Is this normal? If yes, then I have to guess the problem is with my sending unit, but if it is not normal and I should have a constant 12V going back to the fuel tank, and it is blinking where it comes out of the dash harness, and suggestions on my next step?
Thanks
Frank
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
The blinking is an effect of the ICVR (instrument cluster voltage regulator) and is normal. The signal to the sending unit is not a constant 12 volts, it's downstream of a gauge that's powered by a pulsed 5-volt supply (the ICVR).
Check that the fuel gauge pegs to FULL by removing the signal going to the fuel gauge and grounding it. If that does not work, then check the ground at the sending unit.
I am not able to verify your probing locations shown in your pictures, but I think it's a moot point since this is not the place I would be looking. If everything worked with the old tank, you need to focus on the wiring near the tank (which is where the gauge feed from the dash connects to the sending unit, and where the sending unit grounds). These are the only things that could have changed.
Check that the fuel gauge pegs to FULL by removing the signal going to the fuel gauge and grounding it. If that does not work, then check the ground at the sending unit.
I am not able to verify your probing locations shown in your pictures, but I think it's a moot point since this is not the place I would be looking. If everything worked with the old tank, you need to focus on the wiring near the tank (which is where the gauge feed from the dash connects to the sending unit, and where the sending unit grounds). These are the only things that could have changed.
Thread Starter
|
Elder User
Joined: Jul 2011
Posts: 609
Likes: 1
From: Stockholm, NJ
Thanks for the reply. To ground out the power wire near the tank (where I used the test light to see the blinking), all I have to do is run a wire into the female connector (it was a pull-apart connector) and then ground that to the frame? At that point, since the power wire is disconnected, it really doesn’t matter about the ground on the sending unit, right?
Thread Starter
|
Elder User
Joined: Jul 2011
Posts: 609
Likes: 1
From: Stockholm, NJ
I bought a new sending unit and a new wire harness for the unit. I have the pulsed power back to the connector, but as soon as I connect the sending unit wire (blue in picture) it grounds out the power wire (green) and pegs the gauge. If I disconnect the sending unit ground from the frame, then power will flow through from green to blue, but I get no gauge reading.
I don't understand why the sending unit would be grounding out the power wire. There are only two wires here. A power wire and a ground. THis shouldn't be this hard.
I don't understand why the sending unit would be grounding out the power wire. There are only two wires here. A power wire and a ground. THis shouldn't be this hard.
Rusty Roller
Joined: Oct 2011
Posts: 1,423
Likes: 5
From: Santa Cruz Mountains
Hi
You keep saying "power". The sender sends a "ground" signal to the gauge. When the wire back there at the sender is put to ground it acts as if the sender is sending a "full" signal up to the gauge. When the tank is empty the sender sends a "open ground", so to speak, signal to the gauge; and the gauge reads empty.
Ground the wire back there, from the gauge, and see if the gauge reads full. Report back.
.
You keep saying "power". The sender sends a "ground" signal to the gauge. When the wire back there at the sender is put to ground it acts as if the sender is sending a "full" signal up to the gauge. When the tank is empty the sender sends a "open ground", so to speak, signal to the gauge; and the gauge reads empty.
Ground the wire back there, from the gauge, and see if the gauge reads full. Report back.
.
Certified Thread Hijacker
Joined: Aug 2001
Posts: 14,441
Likes: 60
Keep in mind with a 38 gallon tank, it will read FULL until you have used half the tank of fuel or have around 19 gallons. Then the gauge will start reading normally.
Also, there is no "power" wire at the sender. It is a ground "SIGNAL" wire. The sending unit is a resistance to ground, therefore, at full tank you have full ground, 1/2 tank half ground etc.
Josh
Also, there is no "power" wire at the sender. It is a ground "SIGNAL" wire. The sending unit is a resistance to ground, therefore, at full tank you have full ground, 1/2 tank half ground etc.
Josh
Trending Topics
Thread Starter
|
Elder User
Joined: Jul 2011
Posts: 609
Likes: 1
From: Stockholm, NJ
THanks for the replies. If I understand you all correctly, when I have the sending unit attached to the wire that runs up to the gauge, and I use a test light to pierce that wire, I should see no 'light' because it is not sending power, rather, it is grounding it out. If that is correct, then I think everything is working correctly. I have about 3/4 tank of gas in truck and the gauge is pegged past full, but that's because it won't really start giving a 'reading' until I get down below 19-gallons.
Frank
Frank
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
Top 10 Most Expensive Ford Trucks Ever Sold on Bring a Trailer
Joe Kucinski
2027 Ford Super Duty Buyer's Guide (Every Model, Engine, & Package)
Brett Foote
Top 10 Ford Truck Tragedies
Joe Kucinski
AEV FXL Super Duty - the Super Duty Raptor Ford Doesn't Make
Brett Foote
Lobo Vs Lobo: Proof the F-150 Lobo Should Be Even Lower!
Michael S. Palmer
Ford's 2001 Explorer Sportsman Concept Looks For a New Home
Verdad Gallardo
10 Best Ford Truck Engines We Miss the Most!
Joe Kucinski
2026 Shelby F-150 Off-Road: Better Than a Raptor R?
Brett Foote
2027 Super Duty Carhartt Package First Look: 12 Things You NEED to Know!
Michael S. Palmer
Elder User
Joined: Aug 2011
Posts: 685
Likes: 0
From: Cape Coral, Florida
So LMC sent me my new 38-gal tank and all went fine with install except I still have no reading on my gas gauge. The gauge worked when the sending unit was in the old tank and also worked after my buddy soldered on the extended pickup. To make sure it was getting power, I put a test light into the connector where the sending unit pigtail connects to and my test light was blinking. Not a full constant light. I then disconnected the big wiring clip under the hood and sure enough, when I tested two of the pins, they were blinking as well. The attached photos show where I am getting the blinking test light readings.
Is this normal? If yes, then I have to guess the problem is with my sending unit, but if it is not normal and I should have a constant 12V going back to the fuel tank, and it is blinking where it comes out of the dash harness, and suggestions on my next step?
Thanks
Frank
Is this normal? If yes, then I have to guess the problem is with my sending unit, but if it is not normal and I should have a constant 12V going back to the fuel tank, and it is blinking where it comes out of the dash harness, and suggestions on my next step?
Thanks
Frank
Thanks
Posting Guru
Joined: Jul 2011
Posts: 2,104
Likes: 0
From: Virginia Beach, VA
I'm on my second send back from LMC and still can't get a tank that isn't destroyed by the time in gets to my front porch. They put no protection in the box so all the seams are bent and split. I haven't been able to install it yet but I hope its good.
Thread Starter
|
Elder User
Joined: Jul 2011
Posts: 609
Likes: 1
From: Stockholm, NJ
This is my second tank. The first one lasted two fill-ups before it cracked after something kicked up from the road. LMC did warranty it and when they shipped the second tank, they double-boxed it and had foam all around the inner box. That's probably how they should always ship it, but it had to come UPS Freight the second time.
Thread
Thread Starter
Forum
Replies
Last Post
77f250400
1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks
2
Jan 8, 2011 11:19 AM