Toyota 79 series fuel gauge
Submitted: Sunday, Mar 31, 2024 at 08:12
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@Yackandandah
Does anyone know of a fuel gauge to suit a original 79 series fuel sender. The full resistance is 12-18 ohms, empty is 405-415 ohms. I have not been able to find one that works with these values.
I have a 79 series 2011 single cab that came with one 90l tank. I have fitted a genuine Toyota 90l tank to the rear & connected it up to the existing wiring looms. The dash gauge has only one fuel gauge & I have used a relay to switch the gauge between tanks. This works, but for some reason the gauge takes 5 minutes to switch between tanks.
I would like to be able to read both tanks fuel level.
Thanks, Kevin
Reply By: RMD - Sunday, Mar 31, 2024 at 09:30
Sunday, Mar 31, 2024 at 09:30
G'day Kevin.
Seeing you have used a relay for the change over, couldn't you simply use that switch to direct the sender signal to the gauge and not have the relay? Maybe need to run a wire or two to make the connections. Does you fuel gauge read the level while ignition is off? If you turn ignition OFF and then select other tank does it then sense straight away?
You may have to make it kill power to the gauge system when the change over takes place. IE, like ign OFF and then ON so the gauge type senses that level from switch ON.
I had a similar thing with a gauge from a Daihatsu tank. ie Toyota, and it liked reading from switch ON and not from a simple change over.
AnswerID:
645578
Reply By: Member - Racey - Sunday, Mar 31, 2024 at 09:41
Sunday, Mar 31, 2024 at 09:41
Some fuel gauges have a bimetal mechanism to avoid fluctuations due slopping in the tank. The delay you are experiencing maybe due to the heating/cooling of the bimetal in the gauge.
Cheers
Racey
AnswerID:
645579
Reply By: tonysmc - Sunday, Mar 31, 2024 at 10:45
Sunday, Mar 31, 2024 at 10:45
Hi Kevin,
I’m also thinking if using a relay has caused the issue. I have a 75 series with two tanks and only the one original gauge. I have used a 6 pin, on-on toggle switch with no relay and it reads the levels in either tank straight away. Slowly up or down but within a few seconds. If you could somehow
test it by bypassing the relay and see if that helps?
Tony
AnswerID:
645580
Reply By: @Yackandandah - Sunday, Mar 31, 2024 at 12:14
Sunday, Mar 31, 2024 at 12:14
Just to clarify.
The purpose of the relay is so that the single gauge switches to the tank that is selected from the sub/main tank switch. The delay in the gauge switching to the active tank, which is exactly 5 min, is not caused by the relay. I have metered the input going into the gauge & it switches instantly. As the switch time is exactly 5 minutes I am assuming that it is ECU related.
AnswerID:
645583
Follow Up By: RMD - Sunday, Mar 31, 2024 at 13:20
Sunday, Mar 31, 2024 at 13:20
Possibly your vehicle has a trip computer and that is confused until it verifies over time, ie, 5 mins, the reading is the same. So you have answered your own question it seems.
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Reply By: qldcamper - Sunday, Mar 31, 2024 at 13:54
Sunday, Mar 31, 2024 at 13:54
Mightn't be that simple.
To start with your gauge is working as it should being a heavily dampened dual coil movement to stop the sudden movements from sloshing. Not designed to respond quickly, the dual tank models have different systems.
Also consult a wiring diagram for your exact model, I have seen models that have
A module between the sender and dash cluster, but not sure what tank arrangement that was on, so the instrument could operate on a completely different scale to that of the tank sender.
AnswerID:
645584