Fuel Gauge.
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Mountain Pass
Joined: Apr 2002
Posts: 230
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Fuel Gauge.
In an earlier post, someone was talking about fuel gauge problems. Mine aren't working too well either. I have a 71 F-100 custom and neither guage works well. What I mean is that regardless of which tank I have it switched too, the guage never gets above half and is usually at empty. I checked the main tank sender and it seems in good order (I didn't know the specs so I wasn't sure if the resistance it was offering was in spec or the resistance per angle differential if they worry about that kind of thing 
In that previous message, they mentioned the instrument panel voltage regulator or something like that. Mine's there, it's got 12 v on one side, but it putting out a slow PDC on the other side. I didn't have a storage scope to get a good look at what the shape was
, but it seemed to slowly pulsate from zero to 7 or 8 volts about every second according to my DVM. (I just moved and I don't know where my old VOM is. I might have gotten a better idea from that one.)
Does this sound right? Is this thing supposed to put out a pulsating DC? Are these expensive, and if not where do you get them. I don't have to tell you that this one stumped 'em at Kragen's pretty easily although to give 'em credit, I wasn't even sure what to tell them it was.
In that previous message, they mentioned the instrument panel voltage regulator or something like that. Mine's there, it's got 12 v on one side, but it putting out a slow PDC on the other side. I didn't have a storage scope to get a good look at what the shape was
, but it seemed to slowly pulsate from zero to 7 or 8 volts about every second according to my DVM. (I just moved and I don't know where my old VOM is. I might have gotten a better idea from that one.)Does this sound right? Is this thing supposed to put out a pulsating DC? Are these expensive, and if not where do you get them. I don't have to tell you that this one stumped 'em at Kragen's pretty easily although to give 'em credit, I wasn't even sure what to tell them it was.
Post Fiend
Joined: Feb 2000
Posts: 5,130
Likes: 8
From: Brea CA
Fuel Gauge.
Your Instrument voltage regulator (IVR) sounds like it’s working correctly. If you have a scope, you will see the waveshape is close to what you describe. The peak and pulsewidth will vary depending on what the sender resistance is at the moment. The sender is 10 ohms or less when full and 73 or more ohms when empty.
Try this quick check. With the key in accessory, pull off the orange wire on the tank behind the seat and ground it to chassis. The fuel gauge should go past full and peg out. If it does, the circuit is working ok and the senders are suspect. If it doesn’t peg out, then either the gauge, wiring or IVR is bad. You can ground the leads to the temp. or oil sender and they should peg out too. This will tell you if the IVR is really bad or it’s something else. Good luck!
Barry
Try this quick check. With the key in accessory, pull off the orange wire on the tank behind the seat and ground it to chassis. The fuel gauge should go past full and peg out. If it does, the circuit is working ok and the senders are suspect. If it doesn’t peg out, then either the gauge, wiring or IVR is bad. You can ground the leads to the temp. or oil sender and they should peg out too. This will tell you if the IVR is really bad or it’s something else. Good luck!
Barry
New User
Joined: Jan 2008
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Fuel Gauge.
Here is a page on my web site that might be helpful to you.
http://www.clubfte.com/users/mil1ion/FordIllustrations.html
[font color=red]Dennis
Calgary,Alberta,Canada[/font]
[link:www.ford-trucks.com/guidelines.html|FTEModerator]
http://www.clubfte.com/users/mil1ion/Minimorleytruck.JPG
http://www.clubfte.com/users/mil1ion/Mil1ion.html
[font color=red]
Please Don't Ask Me Any Tough Questions,
"I'm Saving My Memory For When I Develop Alzheimer's" [/font]
[font color=blue]78 F-150 429CJ,Silver,Explorer Pkg.
[/font]
http://www.clubfte.com/users/mil1ion/FordIllustrations.html
[font color=red]Dennis
Calgary,Alberta,Canada[/font]
[link:www.ford-trucks.com/guidelines.html|FTEModerator]
http://www.clubfte.com/users/mil1ion/Minimorleytruck.JPG
http://www.clubfte.com/users/mil1ion/Mil1ion.html
[font color=red]
Please Don't Ask Me Any Tough Questions,
"I'm Saving My Memory For When I Develop Alzheimer's" [/font]
[font color=blue]78 F-150 429CJ,Silver,Explorer Pkg.
[/font]
Thread Starter
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Mountain Pass
Joined: Apr 2002
Posts: 230
Likes: 0
Fuel Gauge.
That sounds right. Like I said, I had pulled the sending unit and noticed a nice linear change in the resistance (nothing discontinuous, that is) but under 100 ohms at max.
I had tried grounding the the wire to the sending unit, but didn't get the guage to peg. I'll try it with the oil and water. Those two guages seem to work, but I guess if there is a IVR problem then they would never read very high, and they don't. They never get above 33%.
Again, does anyone know how much they cost? If it's not that much, I'll just throw one in while I've got the instrument panel apart.
Thanks, this is real good help.
I had tried grounding the the wire to the sending unit, but didn't get the guage to peg. I'll try it with the oil and water. Those two guages seem to work, but I guess if there is a IVR problem then they would never read very high, and they don't. They never get above 33%.
Again, does anyone know how much they cost? If it's not that much, I'll just throw one in while I've got the instrument panel apart.
Thanks, this is real good help.
Lead Driver
Joined: Apr 2001
Posts: 6,175
Likes: 21
From: Texas
Fuel Gauge.
Great information!! I too am having fuel guage problems. A real pain since I removed the aux tank and bolted on all of the increased gas sucking equipment. Thanks guys. Technology is amazing!
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