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Old 12-16-2005, 01:01   #1 (permalink)
Lynn Coffelt
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Ford truck fuel gage..empty?

Friends 1998 Ford diesel powerstroke 250 with dual fuel tanks has a
problem with one tank's fuel gage. It reads empty all the time, even when
the tank is full.
Question is, should I be looking for a short or an open? Is the fuel
transmitter a float activated rheostat like in the olden days, or???????
Any tips are appreciated before I bundle up and brave the wind and snow
to check it out.
Thanks in advance,
Lynn


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Old 12-16-2005, 07:01   #2 (permalink)
Backyard Mechanic
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Re: Ford truck fuel gage..empty?

"Lynn Coffelt" <coffelt2@comcast.net> wrote:

> Friends 1998 Ford diesel powerstroke 250 with dual fuel tanks has
> a
> problem with one tank's fuel gage. It reads empty all the time, even
> when the tank is full.
> Question is, should I be looking for a short or an open? Is the
> fuel
> transmitter a float activated rheostat like in the olden days,
> or???????
> Any tips are appreciated before I bundle up and brave the wind
> and snow
> to check it out.


So... let me get this straight. a dual tank machine, and presumably the
owner would have some clue as to how many miles to expect per tank.

Where the normal practice would be to drive/run 2/3 of the expected
capacity from a full tank.. then switch to the one with a gage.

That must be a helluva friend. I mean, even if he's plowing surely it
could wait for a break in the weather. Just switch to working gauge when
he drops the blade.

Use a voltmeter, not ohmmeter, two reasons... it's NOT 12v so not
confusing.. mistake can blow your ohmmeter, start at the switch with key
on

looking for zero to five volts (which is what gage supplies) and the
sender grounds it

full tank always was near or no resistance (a short) so youre looking at
straight five volts until you come to the break in the wire or bad
connection



--
Yeh, I'm a Krusty old Geezer, putting up with my 'smartass' is the price
you pay..DEAL with it!
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Old 12-16-2005, 10:01   #3 (permalink)
Lynn Coffelt
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Re: Ford truck fuel gage..empty?


"Backyard Mechanic" <pettyfog@yaywho.com> wrote in message
news:Xns972E57CA37D88pettyfogery@207.115.17.102...
> "Lynn Coffelt" <coffelt2@comcast.net> wrote:
>
> > Friends 1998 Ford diesel powerstroke 250 with dual fuel tanks has
> > a
> > problem with one tank's fuel gage. It reads empty all the time, even
> > when the tank is full.
> > Question is, should I be looking for a short or an open? Is the
> > fuel
> > transmitter a float activated rheostat like in the olden days,
> > or???????
> > Any tips are appreciated before I bundle up and brave the wind
> > and snow
> > to check it out.

>
> So... let me get this straight. a dual tank machine, and presumably the
> owner would have some clue as to how many miles to expect per tank.
>
> Where the normal practice would be to drive/run 2/3 of the expected
> capacity from a full tank.. then switch to the one with a gage.
>
> That must be a helluva friend. I mean, even if he's plowing surely it
> could wait for a break in the weather. Just switch to working gauge when
> he drops the blade.
>
> Use a voltmeter, not ohmmeter, two reasons... it's NOT 12v so not
> confusing.. mistake can blow your ohmmeter, start at the switch with key
> on
>
> looking for zero to five volts (which is what gage supplies) and the
> sender grounds it
>
> full tank always was near or no resistance (a short) so youre looking at
> straight five volts until you come to the break in the wire or bad
> connection


Thanks Krusty,
(Friend thanks too) I think I've got it. The gage sources 5 volts, and
the tank sender grounds this through a rheostat (or equivalent), with a near
zero resistance to ground indicating a full tank?
Sounds like a possible short to ground somewhere along the path from
the switch to the sender (or maybe the switch or sender themselves)
Friend says Krusty can't be that bad.
Lynn



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Old 12-16-2005, 11:01   #4 (permalink)
Backyard Mechanic
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Re: Ford truck fuel gage..empty?

"Lynn Coffelt" <coffelt2@comcast.net> wrote:



>>
>> Use a voltmeter, not ohmmeter, two reasons... it's NOT 12v so not
>> confusing.. mistake can blow your ohmmeter, start at the switch with
>> key on
>>
>> looking for zero to five volts (which is what gage supplies) and the
>> sender grounds it
>>
>> full tank always was near or no resistance (a short) so youre looking
>> at straight five volts until you come to the break in the wire or bad
>> connection

>
> Thanks Krusty,
> (Friend thanks too) I think I've got it. The gage sources 5
> volts, and
> the tank sender grounds this through a rheostat (or equivalent), with
> a near zero resistance to ground indicating a full tank?
> Sounds like a possible short to ground somewhere along the path
> from
> the switch to the sender (or maybe the switch or sender themselves)


Now I am confused.. remember, the sender grounds.

In the legacy case, taking the wire off an oil, temp, or gas tank sender
causes gauge needle to drop to 'zero'.. and grounding it sends the gauge
to full or high or hot.. ie, the opposite of no needle movement.


thus you are looking for the source point of a disconnect.. not a
'short'. On the gauge side of the failure point, the wire should read 5
volts. ignore fluctations, if any.

Be aware that some think a 'short' means a break.. in reality, it's
connecting something that shouldnt be connected.

--
Yeh, I'm a Krusty old Geezer, putting up with my 'smartass' is the price
you pay..DEAL with it!
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Old 12-16-2005, 12:02   #5 (permalink)
Lynn Coffelt
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Posts: n/a
Re: Ford truck fuel gage..empty?

> Now I am confused.. remember, the sender grounds.
>
> In the legacy case, taking the wire off an oil, temp, or gas tank sender
> causes gauge needle to drop to 'zero'.. and grounding it sends the gauge
> to full or high or hot.. ie, the opposite of no needle movement.
>
>
> thus you are looking for the source point of a disconnect.. not a
> 'short'. On the gauge side of the failure point, the wire should read 5
> volts. ignore fluctations, if any.
>
> Be aware that some think a 'short' means a break.. in reality, it's
> connecting something that shouldnt be connected.


Well, Gee Whiz, I was wondering how you could be so bone-headed.......
Now I see that in my original trouble description, I said (but did not mean
it) that the tank gage always read empty. BUT I SHOULD HAVE said that it
always reads "FULL".

Very sorry!

Maybe I'm getting too old to think and type at the same time!

Thanks again, Krusty!
Lynn (and friend)



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Old 12-16-2005, 12:02   #6 (permalink)
Backyard Mechanic
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Re: Ford truck fuel gage..empty?

"Lynn Coffelt" <coffelt2@comcast.net> wrote:



>> Be aware that some think a 'short' means a break.. in reality, it's
>> connecting something that shouldnt be connected.

>
> Well, Gee Whiz, I was wondering how you could be so
> bone-headed.......
> Now I see that in my original trouble description, I said (but did not
> mean it) that the tank gage always read empty. BUT I SHOULD HAVE said
> that it always reads "FULL".
>
> Very sorry!
>
> Maybe I'm getting too old to think and type at the same time!


Aw, crap! That changes things JUST A LITTLE!!!!.

Once you've determined which wires carry 12 volts (remember fuel pump
and/or relay) test wire with FP's running, switches in both positions.

You can eliminate them.

THEN try to determine which wires head toward fuel tank and use your
ohmmeter with ign switch off.

Hopefully the working sender shows 'not a full tank"... to make them
easier to distinguish.

Another thought... with switches in both positions, each time, do a 'tug
test' along the path of the wiring. Be advised, you may well have a bad
sender, and that's in-tank.

But - unlike a gasoline model - that tank could be, with sensible
precautions, removed inside a garage.

Like no open flames or things that spark, like a drill or compressor and
leave gar door cracked at bottom.

--
Yeh, I'm a Krusty old Geezer, putting up with my 'smartass' is the price
you pay..DEAL with it!
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Old 12-16-2005, 15:01   #7 (permalink)
Shoe Salesman
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Re: Ford truck fuel gage..empty?


>
> In the legacy case, taking the wire off an oil, temp, or gas tank sender
> causes gauge needle to drop to 'zero'.. and grounding it sends the gauge
> to full or high or hot.. ie, the opposite of no needle movement.


I think that's wrong/opposite, if you yank the wire off of the fuel sender I
*think* the fuel gauge will go full. (maybe chevys are that way and ford
isn't?) Also, the first place to look is the switch(probably built into the
fuel line switch), but since your crawling under it anyway visually inspect
everything you can under there first. If you get a book with a wiring
diagram it will make the diagnoses oh-so much easier. Make your friend buy
one, you will probably need it again anyway :)


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Old 12-17-2005, 06:01   #8 (permalink)
PCK
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Re: Ford truck fuel gage..empty?


"Shoe Salesman" <someone@microsoft.com> wrote in message
news:N8Gof.3737$pE4.2894@tornado.socal.rr.com...
>
>>
>> In the legacy case, taking the wire off an oil, temp, or gas tank sender
>> causes gauge needle to drop to 'zero'.. and grounding it sends the gauge
>> to full or high or hot.. ie, the opposite of no needle movement.

>
> I think that's wrong/opposite, if you yank the wire off of the fuel sender
> I *think* the fuel gauge will go full. (maybe chevys are that way and ford
> isn't?) Also, the first place to look is the switch(probably built into
> the fuel line switch), but since your crawling under it anyway visually
> inspect everything you can under there first. If you get a book with a
> wiring diagram it will make the diagnoses oh-so much easier. Make your
> friend buy one, you will probably need it again anyway :)
>

chevy and ford are two totally different types of gauges
chevy`s are darsenal movements and i think fords are heated bimetals


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Old 12-17-2005, 10:01   #9 (permalink)
Sharon K.Cooke
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Posts: n/a
Re: Ford truck fuel gage..empty?

PCK wrote:
>
> "Shoe Salesman" <someone@microsoft.com> wrote in message
> news:N8Gof.3737$pE4.2894@tornado.socal.rr.com...
> >
> >>
> >> In the legacy case, taking the wire off an oil, temp, or gas tank sender
> >> causes gauge needle to drop to 'zero'.. and grounding it sends the gauge
> >> to full or high or hot.. ie, the opposite of no needle movement.

> >
> > I think that's wrong/opposite, if you yank the wire off of the fuel sender
> > I *think* the fuel gauge will go full. (maybe chevys are that way and ford
> > isn't?) Also, the first place to look is the switch(probably built into
> > the fuel line switch), but since your crawling under it anyway visually
> > inspect everything you can under there first. If you get a book with a
> > wiring diagram it will make the diagnoses oh-so much easier. Make your
> > friend buy one, you will probably need it again anyway :)
> >

> chevy and ford are two totally different types of gauges
> chevy`s are darsenal movements and i think fords are heated bimetals


Just about every automaker uses this type of movement now:
auhttp://students.concord.edu/murphypv/NEETS/Chapter%2052%20Summary.htm
The bimetallic strip is really old stuff. The difference between a Ford (and
Chrysler) vs. GM fuel SENDER is that the first start with high ohms resistance
for full, and low resistance for empty; GM does it the other way. Grounding a
Ford sender will send the gauge high.
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Old 01-02-2006, 08:01   #10 (permalink)
fireater
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Posts: n/a
Re: Ford truck fuel gage..empty?

Lynn Coffelt wrote:
> Friends 1998 Ford diesel powerstroke 250 with dual fuel tanks has a
> problem with one tank's fuel gage. It reads empty all the time, even when
> the tank is full.
> Question is, should I be looking for a short or an open? Is the fuel
> transmitter a float activated rheostat like in the olden days, or???????
> Any tips are appreciated before I bundle up and brave the wind and snow
> to check it out.
> Thanks in advance,
> Lynn
>
>

step one:
disconnect the wire at the tank and check for power by shorting it to
ground .... does gauge go to full? (if yes check to see if tank is
grounded (plastic tank?) if ground is ok replace fuel sending unit(note
fuel units in ford became shitty. they are ceramic with carbon coating
for a rheostat and the carbon wears off... no connection))
step 2 : if thats not it then find the dual tank switch and disconnect
the wiring to the gauges... check wire for continuity from switch to
sending unit. (obviously if it works on one tank the problem is either
with the switch or the wiring to the other tank .)
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