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TR7 Fuel Gauge & Sender

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redbulletv8
Wedgling
Posts: 4
Joined: 12 Feb 2020 07:12

TR7 Fuel Gauge & Sender

Postby redbulletv8 » 25 Apr 2020 19:13

I have a fuel gauge that does not work,I took the cluster out and found that the flexible track was damaged causing an open circuit.This has been replaced and on refitting cluster the gauge still did not work.I have changed it for one off a spare cluster I had and this one reads full when I know it is not.I used a potentiometer to find 1/2 full and that needed 1.25k.
I have took a reading from the sender and get 155 ohms,I have no idea of the range on the sender from empty to full so this reading does not mean much although it alters if I shake the car from side to side.
Does anyone know the sender range at all?
I have a feeling the gauge is faulty so it probably needs replacing anyway.
I have checked all the earths and cleaned them up and cleaned and tightened all connectors as the ones on the tank were a little loose and corroded.
Any feedback would be appreciated.

saabfast
TRiffic
Posts: 1821
Joined: 03 Feb 2006 08:17
Location: Royal Tunbridge Wells

Re: TR7 Fuel Gauge & Sender

Postby saabfast » 25 Apr 2020 21:29

When I got my car the gauge just read 'full' all the time. I changed the gauge (for a s/h one) and it has worked OK since. Not sure why but they seem to fail showing either empty or full.
Alan
Saab 9-5 2.3t Vector Auto Estate Stage 1
Saab 9-3 2.0 SE Turbo Convertible
'81 TR7 DHC
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Beans
TRemendous
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Re: TR7 Fuel Gauge & Sender

Postby Beans » 25 Apr 2020 23:11

Could also be that you have a punctured float, or the sender itself is at fault
Image
1976 TR7 FHC (currently being restored ...)
1980 TR7 DHC (my first car, a.k.a. Kermette)
1981 TR7 FHC (Sprint engined a.k.a. 't Kreng)

http://www.tr7beans.blogspot.com/

redbulletv8
Wedgling
Posts: 4
Joined: 12 Feb 2020 07:12

Re: TR7 Fuel Gauge & Sender

Postby redbulletv8 » 26 Apr 2020 16:49

Perhaps if a resistance in ohms can be referenced to the 1/4, 1/2, and 3/4 full marks on a known good gauge and a resistance range of a known good sender can be found this could be placed on the help pages.
I will contact S&S after lock down and see if they have a gauge for sale.
Thank you for your replies.

Hasbeen
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Re: TR7 Fuel Gauge & Sender

Postby Hasbeen » 27 Apr 2020 00:12

The first time I filled the tank on my 7, after building it from 2 wrecks, the fuel gauge read only 3/4 when the tank was filled up the filler neck. When checked I found the float had something like 15 to 20% of its capacity full of petrol.

Knowing that wood swells when wet with water, I drilled a small hole in the float to get the fuel out, then plugged the hole with a wooden plug carved from a Kebab stick, & tapped ti gently into the hole, trimming it almost flush, hoping that wood swelled in petrol in the way it did with water. The gauge still didn't read totally full, but is only half the needle width below full.

That was about1993, & the float was still empty when last inspected about 3 years ago, & the gauge still reads the same 27 years later. I think wood must swell in petrol.

Hasbeen

Beans
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Re: TR7 Fuel Gauge & Sender

Postby Beans » 27 Apr 2020 16:07

Hasbeen wrote: ... That was about1993, & the float was still empty when last inspected about 3 years ago, & the gauge still reads the same 27 years later. I think wood must swell in petrol ...

The better "bodge"repairs :mrgreen:
Image
1976 TR7 FHC (currently being restored ...)
1980 TR7 DHC (my first car, a.k.a. Kermette)
1981 TR7 FHC (Sprint engined a.k.a. 't Kreng)

http://www.tr7beans.blogspot.com/

saabfast
TRiffic
Posts: 1821
Joined: 03 Feb 2006 08:17
Location: Royal Tunbridge Wells

Re: TR7 Fuel Gauge & Sender

Postby saabfast » 27 Apr 2020 19:10

Typical, got the 7 out on Sunday to clean for next weeks 'Classics for Carers' and my gauge went straight to 'Full'! Its been fine for years.
Alan
Saab 9-5 2.3t Vector Auto Estate Stage 1
Saab 9-3 2.0 SE Turbo Convertible
'81 TR7 DHC
Image

redbulletv8
Wedgling
Posts: 4
Joined: 12 Feb 2020 07:12

Re: TR7 Fuel Gauge & Sender

Postby redbulletv8 » 22 Jun 2020 20:01

I have fitted a replacement gauge from S&S and all is good.
Before fitting I made a note of the resistance between the 3 terminals and looking at the back of the gauge if you measure between the top terminal and the r/h lower one is around 545 ohms.
Between the top terminal and the l/h lower one is around 300 ohms.
Between the 2 lower terminals is around 245 ohms.
These readings I hope will save someone the hassle i've had.

Beans
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Joined: 15 Mar 2006 19:29
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Re: TR7 Fuel Gauge & Sender

Postby Beans » 24 Jun 2020 09:00

Thx, good info!
Image
1976 TR7 FHC (currently being restored ...)
1980 TR7 DHC (my first car, a.k.a. Kermette)
1981 TR7 FHC (Sprint engined a.k.a. 't Kreng)

http://www.tr7beans.blogspot.com/

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