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MG TD TF 1500 - Fuel warning light on with engine on

Hi. Now that the good weather arrives I would like to enjoy my TD as much as possible, but I have found a problem that I do not know how to solve. I have searched the archive and I have not seen anything like it, so I ask for your help.

With the fuel tank full and ignition on, I have a fuel light off, but when I start the engine, the light comes on intermittently, increasing according to engine revolutions. I have checked the circuit and everything is correct, at least in appearance.
Gabriel Martínez

Do you have a sound earth connection to the tank or fuel level indicator casing?
Dave H
Dave Hill

I was thinking the same thing Dave, but why only when the engine is running? Is the charging circuit working properly, no shorted wires under the dash? PJ
PJ Jennings

The best way to start looking for this fault is to separate the fuel level sender from the rest of the circuit to do so just remove the bullet connector which has the green and black wire going to it, the connector is found next to the rear left chassis member, under the rear apron. If you still have the fault then the problem is not with the sender unit. If the lamp does not light short the loose green and black wire to ground.

John
J Scragg

The cable that goes to the sending unit has a good connection and is not connected to earth in another place, there is no possible short circuit in sight behind the dashboard. I have disconnected the cable from the sending unit and the light goes out with a low amount of fuel, but I have not tried to start the engine with the cable disconnected, tomorrow I will try it.
Gabriel Martínez

Don't forget that the copper fuel pipe is an earth!
Regards
Declan
Declan Burns

Hello, with the cable disconnected from the fuel sending unit and the engine started the light is always off at low or high rev.
Gabriel Martínez

Time for a good clean-up or replacement of the sending unit.
Lew Palmer

I agree with Lew. Get one with a metal float (From the Frame Up has them), as the plastic floats dissolve and sink in modern fuel. Or if yours is an original Smiths sender with a metal float, you can open it up and repair it. Abingdon and FTFU have gasket sets for them. George
George Butz III

Right, today I filled the tank and La Luz went off half an hour later, but with the vehicle rolling it came back on again. I have driven later with the cable of the fuel sending unit disconnected and the light has not turned on again. It seems to be a problem in the limit or a "capricious" fuel sending unit. Now I have to empty the tank and solve the problem.
My float is new of plastic, but I have saved one metal of a frozen sending fuel unit, I will try to change it.
Gabriel Martínez

A washer comes with the sending unit installation kit. It is to prevent the connector from shorting to ground. Is yours installed? Bud
Bud Krueger

Ok. It is installed.
Gabriel Martínez

It's the small circular gasket shown here. Bud

Bud Krueger

Fact. The plastic float is broken by the area of ​​union with the rod and is filled with fuel. I replaced it with an old brass one.
The slight crack can be seen to the left of the float and it is filled of fuel.

Gabriel Martínez

I have seen that crack many times. It is caused by the wire being too tight at the very end. It actualy pokes a hole in the plastic float.
I used a warm soldering iron to melt the hole closed and relieved the end of the wire by tapering off the inside at the very end of the loop. Then I installed the float by the other end.
Sandy
Sanders

I have discovered the reason for the capricious behavior of fuel light. It seems that there is low intensity of electricity, so that when it should be on it is off if the engine is idling, but if it goes up, then it starts to look more and more. Therefore, I had two problems, one the broken float and the other electric. The latter I must find out why, because the car works well.
Gabriel Martínez

This thread was discussed between 27/03/2019 and 07/04/2019

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