Home » Public Forums » GMCnet » Fuel Sender Resistance
| Fuel Sender Resistance [message #342033] |
Thu, 28 March 2019 11:23  |
Justin Brady
Messages: 769
Registered: April 2015
Location: Bell Buckle, TN
Karma: 11
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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
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| Re: [GMCnet] Fuel Sender Resistance [message #342039 is a reply to message #342035] |
Thu, 28 March 2019 13:04  |
Justin Brady
Messages: 769
Registered: April 2015
Location: Bell Buckle, TN
Karma: 11
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Senior Member |
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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
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| Re: [GMCnet] Fuel Sender Resistance [message #342046 is a reply to message #342042] |
Thu, 28 March 2019 15:59 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Senior Member |
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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 <
gmclist@list.gmcnet.org> wrote:
> Justin Brady wrote on Thu, 28 March 2019 14:07
>> 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
>
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Jim Kanomata
Applied/GMC, Newark,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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Jim Kanomata
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www.appliedgmc.com
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| Re: Fuel Sender Resistance [message #342052 is a reply to message #342033] |
Fri, 29 March 2019 09:57 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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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
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| Re: Fuel Sender Resistance [message #342053 is a reply to message #342052] |
Fri, 29 March 2019 10:13 |
Bill Van Vlack
Messages: 419
Registered: September 2015
Location: Guemes Island, Washington
Karma: 14
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Senior Member |
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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.
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| Re: [GMCnet] Fuel Sender Resistance [message #342058 is a reply to message #342057] |
Fri, 29 March 2019 12:06 |
Stu Rasmussen
Messages: 130
Registered: January 2019
Location: Silverton, OR
Karma: 0
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Senior Member |
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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
On 3/29/2019 9:50 AM, Justin Brady via Gmclist wrote:
>> From my research the factory gauge should have a parallel resistor to act as a buffer to eliminate the fast swings
>
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Stu Rasmussen W7QJ
Silverton, OR
'77 Birchaven
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| Re: Fuel Sender Resistance [message #342064 is a reply to message #342062] |
Sat, 30 March 2019 10:25 |
Bill Van Vlack
Messages: 419
Registered: September 2015
Location: Guemes Island, Washington
Karma: 14
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Senior Member |
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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.
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| Re: Fuel Sender Resistance [message #342065 is a reply to message #342033] |
Sat, 30 March 2019 11:39 |
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RF_Burns
Messages: 2277
Registered: June 2008
Location: S. Ontario, Canada
Karma: 3
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Senior Member |
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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
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| Re: [GMCnet] Fuel Sender Resistance [message #342066 is a reply to message #342065] |
Sat, 30 March 2019 12:18 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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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 <
gmclist@list.gmcnet.org> wrote:
> 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
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| Re: [GMCnet] Fuel Sender Resistance [message #342070 is a reply to message #342035] |
Sat, 30 March 2019 12:48 |
rallymaster
Messages: 662
Registered: February 2004
Location: North Plains, ORYGUN
Karma: -4
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Senior Member |
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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
writes:
> 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 gmclist@list.gmcnet.org> wrote:
Ron & Linda Clark
North Plains, ORYGUN
1978 Eleganza II
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Ron & Linda Clark
North Plains, ORYGUN
78 Eleganza II
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| Re: [GMCnet] Fuel Sender Resistance [message #342098 is a reply to message #342053] |
Sun, 31 March 2019 10:03 |
Richard Denney
Messages: 920
Registered: April 2010
Karma: 9
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Senior Member |
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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 <
gmclist@list.gmcnet.org> wrote:
> 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
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| Re: [GMCnet] Fuel Sender Resistance [message #342103 is a reply to message #342098] |
Sun, 31 March 2019 14:45 |
Justin Brady
Messages: 769
Registered: April 2015
Location: Bell Buckle, TN
Karma: 11
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Senior Member |
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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
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