Low reading temp & fuel gauges

[Sundowner]

Despite the car being fitted with a new voltage stabilizer and a new fuel tank sender unit, the Fuel and Temp gauges on my Sprint are reading about 1/3rd low and I figure its a bad earth causing it.
However, I can't find the earthing point for them.
As far as my electrically challenged eye can see from the wiring diagramme, both sender units are earthed and there are no other earthing points near the gauges.
BUT....There is only 7 volts getting to the fuel tank sender unit. The battery has a reading of 13+ Volts.
Every other earthing point, that I can find, checks out OK.
Where should I look in order to fix this %$@#*&) annoying problem?
Cheers,
Rob

[GTS290N]

A faulty new stabiliser? The stabiliser should give 10v wrt earth - what do you read with your meter?

[Toledo Man]

Have you taken a reading from your votlagae stabilizer? I agree that it could well be faulty.

[Mad Mart]

Check the VS earth. The screws securing the VS must make a good contact with the bodywork as the VS body is the return path to the battery.

[Sundowner]

Thanks for that Gents.
It's Friday evening here now, so I'll check out those points on the VS again tomorrow.
Cheers,
Rob

[SprintMWU773V]

I tend to use a separate earth wire as in my experience they don't earth well on the body.

[MIG Wielder]

It would be worthwhile doing a couple of extra tests. But both gauges reading low would tend to suggest a supply voltage problem rather than an earth as they are earthed separately at opposite ends of the car.
Start the car and let the voltmeter come up to read 13.5 - 14V on the in-car voltmeter.
1. With your digital multimeter check the voltage from the casing of the fuel tank sender unit to a good earth like one of the nuts on the bumper bolt. It should be less than 0.25V. Any more than that and I'd be looking at a bad earth lead or connection ( the black one.).
2. Under the same conditions check from the brass hex on the temperature sender to the earth terminal of the battery. Again look for less than 0.25V. If its more, check the engine earth strap and have the temperature sender out to clean up the thread. ( This one is quite unlikely though).
3. Check the plain Green wire at the input to the voltage stabilizer . You need greater than 12.5V here if it is to work properly. If this voltage is low then its fuse box connections and wiring.
And then as Mart says, check the VS case earthing.
Get back to us if this doesn't help as I have some other measurements you can try.
Tony.

[marko]

I'LL get one of my voltage stabilisers ready to post over the weekend just in case it's that. I'm still testing mine but I cannot see any problem arising in the near future with it, I hope not as I have splashed the cash and have bought 20 of them for me to pass on.

[Mahesh]

My fuel and temp gague we both temperamental, voltage stabiliser replaced, problem solved.

I would concentrate the effort on the voltages in and out of the stabiliser and the earth point behind the dashboard.

[Sundowner]

First of all, I want to let you all know how much I appreciate your help here. Its is very much appreciated.

I switched on the ignition and let the voltage meter come all the way up.
I measured the input side of the voltage stabiliser and found it was receiving just short of 12 volts. I then looked at the output side and it was putting out just short of 10 volts. (This was earthing it against the body of the VS itself. Does this indicate its earthing fully?)

At the same time the temperature sender unit was receiving 8 volts and the fuel sender unit was receiving juts 6.5 volts.

Now I'll get out there again and check out the fuse box points.

Again, Thank You.

Cheers,
Rob

[Sundowner]

I've just cleaned the paint off the bulkhead immediately behind the VS and increased its earthing area.
The input has now increased to 13.1 volts and the output to 10 Volts.
Consequently, both the fuel gauge and the temp gauge are reading higher too at 7 and 9 volts. Its an improvement, but its still not good enough.
I'll keep at it.

The problem I have here is that this car has had a complete and total re-spray, then, whoever re-assembled the thing, didn't remove paint from the earthing points. I've had the emery cloth out several times cleaning up these points. I expect there will be more.

Cheers,
Rob


Now, with the car warmed up and idling at normal operating temperature, the temp gauge reads only to the first mark of the gauge...only about halfway to normal. (this is what its always done)
However, I can only get a 5 Volts reading at the temp sender unit. Where when it was cold with the engine off, but the ignition on, it was reading 9 volts.

I've checked out the fuel tank sender earth by running a separate earth wire to it and it didn't change the reading at all.
I have improved the fuel gauge indication by about 10% by improving the VS earth though.

Rob

[Sundowner]

I checked out the gauges by earthing them out and they are both working properly.
All earths are now OK too.

In summary.....
1) There is 10 volts going from the Voltage Stabiliser to the gauges.
2) There is only 8 or 9 volts getting from the temp gauge to the temp sender and about 7 Volts from the fuel gauge to the fuel sender unit.

So, what do you think is causing the gauges to still read low?

If it cant be fixed, it's something that I can live with....but, I'd rather not.

Cheers,
Rob

[Carledo]

I checked out the gauges by earthing them out and they are both working properly.
All earths are now OK too.

In summary.....
1) There is 10 volts going from the Voltage Stabiliser to the gauges.
2) There is only 8 or 9 volts getting from the temp gauge to the temp sender and about 7 Volts from the fuel gauge to the fuel sender unit.

So, what do you think is causing the gauges to still read low?

If it cant be fixed, it's something that I can live with....but, I'd rather not.

Cheers,
Rob

So, you now have to do it the hard way! Starting at the back of the guages, check every joint in the wiring between the guages and the senders to see where the voltage drop is, there is the connection where the wire fits to the guage, another (for both wires) where the dash loom connects to the main loom and a 3rd (fuel guage only) in the joining block behind the passenger front kick panel temp guage wire colour code is green with blue trace and fuel guage is green with black trace.

Steve