Faulty Fuel Gage
 

Fuel Gage giving mixed readings, when switch on the fuel gage moves, but inconsistent ,even when tank is full the gage moves up and down, and most times shows 1/2 full, any suggestions and help would be most appreciated .

Martyn

Probably the sender unit in the fuel tank.

Info in the How-To's.

It is where the car "throws down the gauntlet" to challenge the owner to a game of Russian roulette ;)

Normally this happens, where some "green plum" has been into the fuel tank to rectify a fuel pump issue, and bends or otherwise knacks the float arm.

So bearing that in mind, check the drivers side module first, then the passenger side if that doesn't work.

There are two separate float level sensors, and the IPK take the average of the two readings to arrive at what is displayed on the gauge ;)

Have fun

Brian :D

Are you getting odd results or warnings from other items, i.e. ABS?

As Brian says someone has most likely been in the tank, as your car is a CDTi I'd check the drivers side first.

If it was a petrol model I'd suggest the passenger side first. Just had to this on a V6 where someone had been messing about fitting the Orange clip ;) That one didn't drop below 3/4 tank no matter what was in there ;)

Russ

Faulty Fuel Gage
 

You guy's are incredible with your suggestions. Keep me busy for a while. Thank you all .


Martyn

I have suspected Brian's diagnosis to be the right one for my inaccurate gauge since I first bought the car. After the low fuel light came on for the first time, I managed to get 28L of diesel into the tank before diesel ran out from under the car. The previous owner's plonker "mechanic" son, had replaced the ITP, doubling over the foam gasket when he fitted it, causing the full tank leak. I refitted it correctly, but from full (which registers as slightly above half on the gauge), to low level light coming on, is around 33L. One day, I'll put a gallon in the boot, then drive 100miles with the light on. I reckon it would do it. So no excuse for running it out of fuel, eh?

Perhaps there could also be a bad electrical connection somewhere?

On mine at least, the total consistency of the gauge would suggest some other fault, eg , a bent float arm.

Yes, if it's consistent. But I don't think Richard3275's was?

I haven't had the privilege of looking closer at a 75/ZT float and sensor, but drawing on experience from other makes, they usually consist of a float at the far end of a very thin and flimsy steel spoke that could easily get bent. This, in turn, is connected to a variable resistor; the same principle as a potentiometer, only arch-shaped. As the float moves up or down, the resistance changes in the electric circuit connected to it, and this change is measured by your gauge.
Such a resistor would normally be kept lubricated by the fuel itself. However, all such resistors are sensitive to buildup of sludge, dirt, grit, and even corrosion. That's one possible source for an inconsistent reading.

Another is probably the cables and connectors themselves. Being exposed as they are to the elements, they cannot be blamed for deteriorating over time. Weak points are especially any connectors or couplings where air, moist, goo and whatnot can make its way in and mess with the electronics. So I'd start looking there.