Fuel gauge problems.

[Jag 1979]

Hello, and its nice to be a member again after many years.

I have a Daimler 1979 series 3 4.2 fuel injection.

The car has just been recommissioned, after not being used for 29 years.
My fuel tanks after being cleaned are about half full, yet my gauge read 0 on both tanks.
The gauge drops below the 0 with the ignition being switched off.

I thought it maybe possible that the fuel senders have frozen in position after being stood for so long?

I have found what looks like a used fuel send in the boot. So, it appears that maybe this problem is not new?

[mike020150]

It wouldn't be impossible for both units to have failed but it does seem unlikely. I would start by testing if any signals are reaching the gauge from the tank senders. Do this by having one person watching the gauge for any signs of movement when, with the ignition switched on, a second person briefly earths the feed wire to the gauge where it attaches to the sender unit. Try the feed wire for each sender. If the gauge moves, the problem is indeed with the sender. If it doesn't, there may be a wiring issue. Bear in mind that the changeover switches are a common source of problems too. Mike.

[Jag 1979]

Thank you for your reply, car electrics are not my strong point.

I took the fuel gauge out yesterday, and run power to it. And the gauge worked fine.
As said, I found an old fuel gauge in the boot along with two old fuel change overs switches.

Are the systems complex on these cars in terms of the fuel wiring problems that can arise?

And as you say, it is possible for both to fail. However, both also say the same fuel among ie 0.
There must be power going to the gauge, as it moves a fraction when the ignition is turned on.

[mike020150]

The wiring is quite simple so it's a matter of testing each wiring run logically until you find the faulty component or wiring break. Try the test in my last post to get started. Mike.

[Jag 1979]

Hello Mike,
Mike I did as you suggested, I earthed the feed from the fuel sender end.
The result was that the fuel gauge rushed to the full mark.
So, therefore is must be both of the fuel sender.
Regards Karl

[mike020150]

Excellent! Now you can have confidence in checking out the senders. Remove each in turn to see if the floats have jammed at their lowest level and can be freed off or if they are totally unserviceable. Mike.

[Jag 1979]

Hello Mike.
I thought that I would simply replace them with new ones.
Regards Karl
Thanks again.