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LJ S dash Fuel Gauge Issue


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#1 LJ2250

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Posted 07 November 2023 - 12:47 PM

My LJ fuel gauge is acting strange and not reading correctly after the car has been running for a few minutes.

 

I recently replaced the sender with a rare spares one as the previous one was dead and the fuel gauge read full all the time, now I have a different problem.

 

When I first start the car the fuel gauge it fine and shows the correct level but after a few minutes it drops down near empty and bounces around there slightly. If I turn the car off for a few minutes and then restart it the gauge goes back to normal initially but again after a few minutes it reverts back towards the empty position again.

 

Has anyone else had a similar issue or know what the problem could be?



#2 nanbar

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Posted 07 November 2023 - 04:50 PM

Mine behaved similarly after changing my sender with a rare spares one. I spoke to Howard Instruments and the lady there said before I bring it to them check the earths (tank properly earthed and in the dash). She reckons most instrument problems are earth related.

I added an earth wire from the one of the tabs on the sender to a screw on the body. I also checked the earth at the dash end and made it better, now the gauge seems to be behaving. I also bench tested my gauge with the old sender connected to a 12V battery, gauge behaved precisely as expected, full was full, empty was empty and it ran smoothly through the range.

Bad earths are not your friend.

Hope this helps.


Edited by nanbar, 07 November 2023 - 04:50 PM.


#3 yel327

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Posted 07 November 2023 - 05:03 PM

You beat me too it. Just don't call them earths!

 

Make sure the - terminal of the battery is bonded to the body, not just to the motor. And check all of the connection to the body from the dash and the dash harness - undo them and clean them up. If the tank has been removed and painted and/or the body where it mounds has been too, run a wire as described above so the tank body is connected to the vehicle body.

 

Most of the stuff on the car is connected to the 0V potential of the battery - terminal, and the body is the return path for any current. If there is a varying resistance involved, like an analogue sender unit in the fuel tank, it will never read right if the tank and the sender aren't at the same potential (0V) as the battery -.



#4 Dr Terry

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Posted 07 November 2023 - 05:17 PM

It's a habit that you won't change Byron.

 

In the world of 'proper' electrical systems, as you are, the term 'earth' is incorrect in this context. However, to most auto electricians it is their 'earth' & even though the car's body (chassis) is floating above ground, it is effectively 'earth' in the 12V realm.

 

Dr Terry



#5 LJ2250

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Posted 07 November 2023 - 05:50 PM

Thanks for the responses everyone, I’ll recheck all of the earths and provide some feed back.



#6 hanra

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Posted 07 November 2023 - 06:30 PM

Lolz

#7 yel327

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Posted 08 November 2023 - 07:19 AM

It's a habit that you won't change Byron.

 

In the world of 'proper' electrical systems, as you are, the term 'earth' is incorrect in this context. However, to most auto electricians it is their 'earth' & even though the car's body (chassis) is floating above ground, it is effectively 'earth' in the 12V realm.

 

Dr Terry

 

Whomever is teaching auto elecs this needs to have their qualifications reviewed. Especially today with the amount of low voltage inverters and grid connected (via caravan inlet plugs) mobile equipment, where there is a huge difference between earth and vehicle chassis ground. While the re-education is happening, they should also have the idea that 12V is low-voltage beat out of them as well!



#8 claysummers

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Posted 08 November 2023 - 07:37 AM

In distribution, they call 240 and 415 LV.

7.5kV is the lowest HV we use, though that is being phased out. No pun intended....

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#9 yel327

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Posted 08 November 2023 - 08:08 AM

240V and 415V are the same thing Clay, same voltage from the same source as far as a safety perspective.

 

Low Voltage is Legislated in Australia across all States and Territories as:

 

50V to 1000V AC.

120V to 1500V DC (but only if ripple free, which means most cheap and nasty dc power supplies must be treated as AC as they have more than 10% ripple).


Anything above that is High Voltage.

 

Yet walk into Bunnings right now, and there on packaging on Xmas lights - safe as it uses Low Voltage!

 

I really concerns me when I see some of the Low Voltage installations in people's vans, trailers and vehicles. Don't get me started on whomever sizes the ELV wiring on the 12V side of the inverters or winches.



#10 gtrboyy

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Posted 08 November 2023 - 07:48 PM

Just the fuel gauge that plays or other gauges & lighting?

 

Seem some do weird things when those metal locating things to dash are loose






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