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Old 02-21-2020, 12:35 PM   #61
JSeery
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Default Re: How Ford Gauge Unit Work

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Originally Posted by grumppyoldman View Post
I just have a simple question, my gauge reads full when tank is full but when it reads about E I only have room for 10 gal. in a 17 gal. tank. Do I need to bend the float arm down or shorten it. Al
What sending unit do you have?
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Old 02-21-2020, 12:39 PM   #62
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Default Re: How Ford Gauge Unit Work

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Originally Posted by Brian View Post
And I have a question too - sorry!
Running 36 fuel tank, original sender, original dash unit, 12 volt conversion, [alternator], runtz on gas gauge, another on oil pressure gauge.
Problem is that upon turning on ignition, needle in fuel gauge will climb and indicate [approximate] fuel level, but then when I start the engine and start driving, the needle goes down below empty and stays there.
Why would this be?
A guess would be some type of wiring issue. You could start by checking the gauge with a "D" cell just to eliminate that. Grounding at the sending unit can be a problem, a jumper wire from the sender to a good known good ground would also be something to try.

Assuming the tank is indeed full and reads full with the ignition switch on, the gauge would be indicating maximum current flow through the gauge and sending unit (or some source to ground). If it drops when the engine starts something is reducing the current flow, as in an open circuit or grounding issue. Is there something somewhere that could move/change when the engine is running?

I would trouble shoot starting at the gauge. Connect a jumper wire to the sender post on the gauge. Once the engine is running and the gauge starts to move toward empty touch the jumper to a known good ground and see it the gauge starts to return to full (I would do this for only a short period of time). If it does the problem is not the gauge.

I would next connect a jumper to the sender unit connection (at the sender unit) and try it again. If the gauge stays on empty there may be a wiring problem between the gauge and the sender. If it moves back toward full in may be the sender itself or a ground issue.

To check between the sender being the issue and a poor ground, connect a jumper to a mounting bolt for the sender and try again. If the gauge stays on empty I would suspect the sender itself if it goes back to full it is most likely a sender grounding issue.

Last edited by JSeery; 02-21-2020 at 02:13 PM.
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Old 07-02-2023, 02:48 AM   #63
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Default Re: How Ford Gauge Unit Work

Quote:
Originally Posted by Brian View Post
And I have a question too - sorry!
Running 36 fuel tank, original sender, original dash unit, 12 volt conversion, [alternator], runtz on gas gauge, another on oil pressure gauge.
Problem is that upon turning on ignition, needle in fuel gauge will climb and indicate [approximate] fuel level, but then when I start the engine and start driving, the needle goes down below empty and stays there.
Why would this be?

I know I'm resurrecting a 3 year old post here, but I'm wondering if Brian ever sorted out his fuel gauge problem where it would start reading ok then dropping back to zero - because I'm having somewhat of a similar problem, but I'm pretty sure I know what's causing mine.


I found the points in the sender unit pitted and dirty, so I disassembled the thing, - yeah, you can disassemble the things if you're careful ! -and filed the points flat to get rid of the pitting, (used wifey's nail file ) got them all clean, sprayed them with electrical contact cleaner, reassembled it, adjusted the little toothed adjusting wheel to get a reasonably accurate reading at the gauge and put it back in the tank.

All was good for half an hour then the needle decided to start wandering before dropping down to empty.


So I pulled the sender back out, cleaned and sprayed the points again, reinstalled it and same thing, except this time it lasted a little longer.

So I've tried this 3 or 4 times now and it keeps happening. If I tap the top of the sender unit while it's in the tank it comes good - (shitty points!?)

I've dissembled the sender unit a couple of times now and I'm happy that everything else is good. Earths out ok. I've earthed the tank to the chassis so I'm not relying on the tank holding straps for my earth to to sender unit.


Somewhere in the dim dark past in the back of my mind I seem to remember something about points (well, ignition points anyway) might have been "coated" to help against pitting, or going resistive. Is that true? Perhaps I've taken that coating off by filing them ?


Wiring's all new and good. I rebuilt and rewired the car. And I'm using a single LM7806 IC heatsinked to the steel dash cluster to drop 12v down to 6v. They're not rated to draw 2 amps, (which is what I measured when the contacts were closed) but the IC's not getting hot, the oil and water gauges are reading ok and I'm measuring 6volts at the ign side of the gauge.



So there ya go folks. What the bloody hell's going on here? Your thoughts ?


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Old 07-02-2023, 11:16 AM   #64
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Default Re: How Ford Gauge Unit Work

Intermittent function is generally caused by an intermittent connection somewhere in the system. If tapping on the sender affects it then it's in there somewhere. It may not be getting a good ground. The ground path is fairly long on a fuel tank back to the frame. The power comes from the battery and passes through both the heating coil in the indicator unit and the heating coil in the sender so it's a pretty long circuit since it runs near the length of the car.

Our dear friend J Seery passed a while back so be aware that old threads are not always the best way to get the help you seek. Don't hesitate to start a new thread. Welcome into the Ford barn.
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Old 07-02-2023, 02:45 PM   #65
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Default Re: How Ford Gauge Unit Work

Yes, I did sort out the problem....I tried another sender unit, but it too had some sort of issue, I can't remember. Then, I found in my stash, yet another sender, a dirty, rusty looking thing, dunno where I got it from. Fitted it and, sweet! I works spot on.
Sorry I can't offer advice as to what was wrong with the original sender unit, I haven't needed to investigate further...if it ain't broke, don't fix it!! If you can find another sender unit, try it, may just work....good luck.
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Old 07-02-2023, 06:47 PM   #66
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Default Re: How Ford Gauge Unit Work

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Thanks for the quick reply fellas.


Sad to hear of the passing of Mr Seery. From what I've gleaned reading over the forum here, he appeared to be a pretty knowledgeable guy. We've lost a couple of good guys in the club of which I'm a member, over the last four years or so. Always sad.

It's probably the same stateside with you guys, but I've noticed that most of us in the Classics & hot rod fraternity are well beyond the age of wisdom teeth !



Well, I'll persist with my fuel gauge issue over a time and when i sort it out I'll stick it up here on the forum as it may be of benefit to others.


Mick
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Old 01-24-2024, 06:07 AM   #67
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Default Re: How Ford Gauge Unit Work

Very belated update on the intermittent fuel sender problem. I ended up pulling the unit back out. Disassembled it on the bench and aggressively filed the points till the pitting was almost gone. Then put it back together. I had to very slightly adjust the tooted adjuster to get the gauge accuracy back, but, touch wood, it's been good ever since.
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Old 01-25-2024, 11:58 AM   #68
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Default Re: How Ford Gauge Unit Work

It is the FREQUENCY of the opening and closing of the points in the sender that is being measured by the gauge end which is calibrated to the sender. In a word, the gauge is measuring FREQUENCY. This is true of all the King Seeley systems, same for the temperature gauge as the gas gauge. It is not a voltage or resistance measurement at the gauge end.
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Old 01-25-2024, 05:09 PM   #69
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Default Re: How Ford Gauge Unit Work

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Very belated update on the intermittent fuel sender problem. I ended up pulling the unit back out. Disassembled it on the bench and aggressively filed the points till the pitting was almost gone. Then put it back together. I had to very slightly adjust the tooted adjuster to get the gauge accuracy back, but, touch wood, it's been good ever since.
..."tooted adjuster" ?????!!!!!!!
Bad typo there. Try ..."toothed adjuster".
You know the little thing I mean in the sender unit. You adjust the mechanical pressure on the points so that they will break easier or not.
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