Fuel Sender Resistance

J

justin brady1

New member
May 4, 2015
727
1
0
Has anyone measured fuel senders?
My tanks read Empty after using exactly 27 gallons of fuel. So roughly half a tank remaining and I'm on empty.

Normally I fill up anyway, but I'd really prefer them to read a little more accurately than this.

My thought is if I know what the resistance on the senders is maybe I can add some inline resistors to get them to read a little more accurately.
As with an airplane I don't really care if they read full accurately I just want them to read empty when I'm actually empty.

--
Justin Brady
http://www.thegmcrv.com/
1976 Palm Beach 455
 
The problem is not the senders, which are 0 - 90 ohm. The tanks transfer
fuel back and forth with terrain changes through the filler manifold. Only
way to be more accurate is to put in separate filler necks.
Jim Hupy

On Thu, Mar 28, 2019, 9:43 AM Justin Brady via Gmclist <

> Has anyone measured fuel senders?
> My tanks read Empty after using exactly 27 gallons of fuel. So roughly
> half a tank remaining and I'm on empty.
>
> Normally I fill up anyway, but I'd really prefer them to read a little
> more accurately than this.
>
> My thought is if I know what the resistance on the senders is maybe I can
> add some inline resistors to get them to read a little more accurately.
> As with an airplane I don't really care if they read full accurately I
> just want them to read empty when I'm actually empty.
>
>
> --
> Justin Brady
> http://www.thegmcrv.com/
> 1976 Palm Beach 455
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
Hey Jim,
Yep I understand how the tanks work and are connected.

To clarify, on level ground not driving with the gas settled when 27 gallons down the fuel gauge reads Empty on both tanks. It should read 1/2 tank on
each, or at least 1/2 tank when averaged between the two tank readings.
--
Justin Brady
http://www.thegmcrv.com/
1976 Palm Beach 455
 
So 0-90 Ohm, Empty is 0 correct?

Ao anything wrong (bad connection etc) should read MORE fuel, rather than less.
Odd as that's not what I'm seeing.

Is there any type of calibration on the gauge itself?
--
Justin Brady
http://www.thegmcrv.com/
1976 Palm Beach 455
 
0 resistance allows more current to flow through the electromagnetic coil
in the gage, and moves the pole piece attached to the needle and spring
assy. More resistance reduces current flow and moves the needle less.
Any loose connections in the circuit usually creates higher resistance
with the same result, except when it creates an open circuit. That results
in no current flow and no needle movement.
Jim Hupy
Salem, Or
78 GMC ROYALE 403

On Thu, Mar 28, 2019, 11:22 AM Justin Brady via Gmclist <

> So 0-90 Ohm, Empty is 0 correct?
>
> Ao anything wrong (bad connection etc) should read MORE fuel, rather than
> less.
> Odd as that's not what I'm seeing.
>
> Is there any type of calibration on the gauge itself?
> --
> Justin Brady
> http://www.thegmcrv.com/
> 1976 Palm Beach 455
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
> So 0-90 Ohm, Empty is 0 correct?
>
> Ao anything wrong (bad connection etc) should read MORE fuel, rather than less.
> Odd as that's not what I'm seeing.
>
> Is there any type of calibration on the gauge itself?

Justin,

Your assumptions are valid. (But they really only go down to about 3 ohms).
the dash instruments are "Air Core" gauges. There are two electromagnetic fields balanced against each other. So, if you have a bad ground on the
instrument, it will report a higher level than is really there. Good luck at finding it.

Matt
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit
 
If your using the old transfer switch , they are eaten by the ethanol and
draws fuel from both tank at times .
You should have replaced them when you rehoused the tank and vent .

On Thu, Mar 28, 2019 at 2:22 PM Matt Colie via Gmclist <

> > So 0-90 Ohm, Empty is 0 correct?
> >
> > Ao anything wrong (bad connection etc) should read MORE fuel, rather
> than less.
> > Odd as that's not what I'm seeing.
> >
> > Is there any type of calibration on the gauge itself?
>
> Justin,
>
> Your assumptions are valid. (But they really only go down to about 3
> ohms).
> the dash instruments are "Air Core" gauges. There are two electromagnetic
> fields balanced against each other. So, if you have a bad ground on the
> instrument, it will report a higher level than is really there. Good luck
> at finding it.
>
> Matt
> --
> Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
> Electronically Controlled Quiet Engine Cooling Fan
> OE Rear Drum Brakes with Applied Control Arms
> SE Michigan - Twixt A2 and Detroit
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmc.com
1-800-752-7502
 
Often there is oxidation on the back of the guage cluster connections and dissimilar metal stufff going on. Also broken solder connections. Added
series resistance. Easy to pull cluster and freshen on the bench.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
There must be damping in the system somewhere, or the gauges would be jumping around all the time. Is that in the sender (mechanical) or the gauge
electronics?

Has anyone attached the senders to an aftermarket or custom readout?
--
Bill Van Vlack
'76 Royale; Guemes Island, Washington; Twin bed, full (DS) side bath, Brazilian Redwood counter and settee tops,455, 6KW generator; new owner a/o mid
November 2015.
 
Also, some automotive gauges are of the 'hot wire' type that indicate by
showing the elongation and contraction of a piece of resistance wire
linked to the needle.

Very common for fuel, water temperature and oil pressure gauges.

I had a Chrysler product once that used an interrupter to modulate the
available current to the gauges (think 'turn signal flasher'). When the
interrupter stuck 'closed' ALL the gauges quickly moved to full scale
and my heart skipped a beat until I figured it out :)

Stu Rasmussen W7QJ
Silverton, OR
gutted '74 Eleganza

>From my research the factory gauge should have a parallel resistor to act as a buffer to eliminate the fast swings
>
 
Justin,
Here is a link on the operation of balance coil gauges and operation of fuel gauges. It might help you to understand it a bit better.

http://www.ppowers.com/mygauge.htm

I've always understood the advantage of a balance coil gauge is its much less sensitive to the vehicle supply voltage and so does not need a voltage
regulator for the gauge. I'm not sure where the meter gets its damping from so the that the meter moves slowly and evenly. It may be due to the
moving magnetic with possibly a separate shorted coil to dampen the meter movement.

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
 
Bruce,
I was hoping to parallel the dash fuel gauge with inputs to two of the EBL analog ports, but I'm not sure that the voltage from the sender would be
very accurate due to the changes in battery voltage on charging, etc. Perhaps one could use a virtual point on WinLog and use battery voltage and
sensor voltage to compensate.

--
Bill Van Vlack
'76 Royale; Guemes Island, Washington; Twin bed, full (DS) side bath, Brazilian Redwood counter and settee tops,455, 6KW generator; new owner a/o mid
November 2015.
 
Bill,
I've never measured the voltage on the fuel level sensors. If I recall, the Analog inputs on the EBL are 5 volt maximum, so a voltage divider might be
needed and a way to limit the voltage to 5V in case of a wiring issue sending more than 5V to the EBL.

In any case, you should be able to scale the reading and compensate for the vehicle voltage. On the other hand, what is the accuracy of the fuel
sensors... maybe +/- 10%.

I always start looking for fuel fillup when I hit the 1/2 tank mark. I need a stretch and pee myself by that point!!

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
 
Yep. Start out in the morning with full fuel tanks. Drive 5 hours at an
average speed of 50 miles per hour. That is 250 miles or so. Figure 8 - 10
miles per gallon. Easily within the range of the GMC's 50 gallon capacity.
Get out, walk about a bit, have lunch, look for a campsite for the night.
Enjoy your trip.
Jim Hupy
Salem, Or
78 GMC ROYALE 403

On Sat, Mar 30, 2019, 9:39 AM Bruce Hislop via Gmclist <

> Bill,
> I've never measured the voltage on the fuel level sensors. If I recall,
> the Analog inputs on the EBL are 5 volt maximum, so a voltage divider might
> be
> needed and a way to limit the voltage to 5V in case of a wiring issue
> sending more than 5V to the EBL.
>
> In any case, you should be able to scale the reading and compensate for
> the vehicle voltage. On the other hand, what is the accuracy of the fuel
> sensors... maybe +/- 10%.
>
> I always start looking for fuel fillup when I hit the 1/2 tank mark. I
> need a stretch and pee myself by that point!!
>
> --
> Bruce Hislop
> ON Canada
> 77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
> http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
> My Staff says I never listen to them, or something like that
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
How do you know how much fuel is in the tank, mine doesn't move off the
full peg until I've driven about 100 miles after a fill-up.

Even after the fill-up, I don't know how much I have in the tanks. The
pump jockeys quit pumping gas as soon as the fill spout belches at them.
I can fill it closer to full than they can, of course, but not in Oregon.
Fixing that problem is on my fix-it list for our visit to Jim K. after
the Spring Rally.

Ron
-----------------
On Sat, 30 Mar 2019 10:18:06 -0700 James Hupy via Gmclist

> Yep. Start out in the morning with full fuel tanks. Drive 5 hours at
> an
> average speed of 50 miles per hour. That is 250 miles or so. Figure
> 8 - 10
> miles per gallon. Easily within the range of the GMC's 50 gallon
> capacity.
> Get out, walk about a bit, have lunch, look for a campsite for the
> night.
> Enjoy your trip.
> Jim Hupy
> Salem, Or
> 78 GMC ROYALE 403
>
> On Sat, Mar 30, 2019, 9:39 AM Bruce Hislop via Gmclist <

Ron & Linda Clark
North Plains, ORYGUN
1978 Eleganza II
 
I’m using an Autometer 90-ohm gauge with new sending units, and yes they do
jump around quite a bit, and rather quixotically at that. When I installed
them two years ago I rang out the gauge lines to confirm the circuits.

They have less damping than the factory gauge, I suspect, but my factory
gauge has been out of use for my whole ownership and I don’t even know why
it was abandoned.

I have fuel level gauges and they work, but my bladder capacity is still
less than my fuel tanks, so my fill-ups tend to be in the 30-35-gallon
range.

Rick “who can’t make sense of the readings surprisingly often” Denney

On Fri, Mar 29, 2019 at 8:35 PM Bill Van Vlack via Gmclist <

> There must be damping in the system somewhere, or the gauges would be
> jumping around all the time. Is that in the sender (mechanical) or the gauge
> electronics?
>
> Has anyone attached the senders to an aftermarket or custom readout?
> --
> Bill Van Vlack
> '76 Royale; Guemes Island, Washington; Twin bed, full (DS) side bath,
> Brazilian Redwood counter and settee tops,455, 6KW generator; new owner a/o
> mid
> November 2015.
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Rick Denney
73 x-Glacier 230 "Jaws"
Off-list email to rick at rickdenney dot com
 
One of my favorite parts of having the motorhome is that I can just pull off any exit, pull to the side of the on ramp get up and pee and be back on
the road in under a minute.
I prefer to drive until I need to refuel. But at this point it's anyone's guess when that is because I read empty 25 gallons too early.

I'll pull the gauge soon and give it a look.
--
Justin Brady
http://www.thegmcrv.com/
1976 Palm Beach 455
 
Ah, youth. I remember when my bladder worked. :)

The senders are notorious, because the tank is large and shallow. The
rheostats are flaky even when fairly new. And the instrument cluster has
flaky grounding, which also should be checked. (I ran a direct ground bus
for my gauges, all of which are Autometer good gauges—$50-60 apiece
quality, not the $39 for three quality.)

When I rang out the lines, I used a Simpson meter at the gauge wire to show
resistance as I changed the sender float (obviously, when the senders were
out of the tanks). Simpson meters have analog d’arsonval meter movements,
and are big enough to read from 10 feet away. I was able to confirm the
resistance range for each sender, and the dash tank selection switch.

But still brakes, acceleration, turns, crowns, and grade causes all manner
of needle wiggling.

Do the new fuel injection systems have a distance to empty calculation? I
like that better than the needle on my modern vehicles.

Rick “whose gauge shows 1/8ish when the tanks will take 35 gallons” Denney

On Sun, Mar 31, 2019 at 3:37 PM Justin Brady via Gmclist <

> One of my favorite parts of having the motorhome is that I can just pull
> off any exit, pull to the side of the on ramp get up and pee and be back on
> the road in under a minute.
> I prefer to drive until I need to refuel. But at this point it's anyone's
> guess when that is because I read empty 25 gallons too early.
>
> I'll pull the gauge soon and give it a look.
> --
> Justin Brady
> http://www.thegmcrv.com/
> 1976 Palm Beach 455
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Rick Denney
73 x-Glacier 230 "Jaws"
Off-list email to rick at rickdenney dot com
 
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