Checking and replacing a fuel sender unit

Here you can get Checking and replacing a fuel sender unit, Safety precautions, and Checking the sender unit in the petrol tank ect.

If the fuel gauge reads empty once you know there’s fuel within the tank, the cause could also be a faulty sender unit the device that measures the extent. Or it’s going to be a faulty gauge or a break within the wiring between the gauge and sender. It is also possible for the fuel tank to read ‘full’ constantly, although the car has travelled some distance and has obviously used an amount of petrol. The cause could also be a fault within the insulation of the wiring, leading to a brief circuit.

Checking and replacing a fuel sender unit

Safety precautions

An empty tank are often more of a risk than a full one. there’s always petrol vapour in it – albeit it’s been empty for months which the slightest heat or spark can explode. Before doing any repair or replacement work on the tank, begin the battery leads, as a precaution against accidental sparks. The sender unit is mounted through the tank wall, and removing it leaves a hole.

If it’s within the tank side, removing it’s going to let petrol gush out. you want to be sure that the reserve is well below the sender hole – and this is often difficult to guage with the gauge not working. You may be ready to check the extent through the filler with a dipstick . as long as all else fails do you have to drain the tank. Note that in Britain you’ll store up to 2 metal cans each holding 2 gallons (9 litres) of petrol, or up to 2 plastic containers each holding 5 litres (1.1 gallons). The cans or containers must be marked and purpose made, and must not be kept within the house.

A few cars have a tank drain plug. Otherwise, try to empty the tank by disconnecting the fuel pipe or pipes. If the tank won’t empty through the pipe, it’s going to be possible to siphon the fuel out through the filler hole, but anti-siphon devices are often fitted. If siphoning is possible, use a special siphon pump. If you are doing not have one, use several feet of clear plastic tube. Push one end to rock bottom of the tank and suck gently at the opposite end. When you see petrol rising within the tube, quickly plunge the opposite end into the can. If you accidentally get petrol in your mouth, spit it out immediately and rinse your mouth out with many clean water. don’t swallow any – it’s poisonous.

Checking the sender unit in the petrol tank

The sender unit could also be fitted within the top or the side of the tank. Often it’s hard to seek out , particularly if it’s on the top, and you’ll need to remove some trim from inside the boot. Most senders are circular. Generally the fuel pipe (or pipes, during a circulating system) is connected thereto. There is an electrical connection to the fuel gauge, and sometimes a other for a low-fuel red light . make sure the connection isn’t loose, which the wiring has not become kinked, or trapped, breaking the insulation and causing a brief circuit.

Ask a helper to observe the fuel gauge, then turn on the ignition. Disconnect the fuel-gauge wire from the sender unit and scratch its bare end against the tank, or the other bare metal on the chassis or bodywork, to earth it. If the gauge needle swings to ‘full’ although the tank is half-full, there’s no electrical fault, but there could also be a mechanical fault within the sender unit, like a detached float. If the needle stays still, try earthing the wire by touching it to an unpainted point on the car body. If the needle moves now, the tank isn’t properly earthed. Remove and clean some of its mounting bolts or screws.

If the needle doesn’t move in the least , there may an opportunity within the wiring. Check the wiring to the gauge with a circuit tester – one lead connected to the wire detached from the sender and therefore the other to the terminal on the gauge. If the tester shows continuity within the wire, the gauge is faulty. If the sender unit is faulty, fit a new one, but note the security precautions.

Removing and refitting a sender unit

Before you remove the sender unit, take precautions against spilling fuel (see right). Then disconnect the fuel pipe if necessary, blocking it with a plug or an old pencil. If there are two pipes, mark them. Disconnect the electric wires. The sender may be fixed by screws or by studs and nuts round the edge. Unscrew them carefully; one snapped stud could mean replacing the whole tank. Often the sender has a bayonet fitting, held on to its seating by an outer locking ring with lugs.

Release this ring by turning it anticlockwise, using a C-spanner. Alternatively, hold a metal bar against a lug and tap gently with a hammer. lookout to not bend the lug. begin the sender carefully. Inside there’s an extended arm attached to a float. If you bend the arm, the gauge becomes inaccurate. there’s usually a tag within the sender hole to make sure that you simply refit the sender the proper way round. Put the sealing ring in situ and tighten the nuts or screws in sequence to spread the pressure . Reconnect the fuel pipe and electric wires, refill the tank and check for leaks.

Checking the fuel tank

A smell of petrol is presumably to return from a fuel-pipe leak (See Checking fuel pipes ). Check also the flexible hose between the tank and therefore the filler, ensuring that its clips are tight. If of these are sound, the tank could also be leaking. Fuel tanks can rust from both inside and out of doors , particularly at rock bottom . Eventually holes may develop. this is often not uncommon in older cars, where a series of small pinholes barely visible to the eye cause a slow, steady loss of fuel.

If a tank is old and leaky, replace it, not only due to the needless loss of fuel but also due to the danger of fireside. A tank mounted inside the bodywork could also be rusted by water trapped in body panels. confirm that there’s no water present, which drain holes are clear. Drill extra drain holes if necessary – but take care of the tank. Plug any new drain holes later with suitably sized rubber bungs.

A tank mounted on the surface usually under the boot or forward of the rear axle – are often dented or holed by knocks , stones or a wrongly placed jack. A dented tank may provides a shorter range between refills, but be serviceable otherwise. Do not plan to repair a tank yourself. If it’s leaking or rusted through, replace it.

Removing and refitting the tank

Empty the tank (see Safety precautions above). Disconnect the fuel pipes and wires, and the breather tube if one is fitted. Loosen the clips on the hose between the filler and therefore the tank, and begin the hose. Renew a perished hose or corroded clips. Tie a bag over the tank opening, for safety.

The tank could also be held by bolts around its flange or by metal straps. Bolts on the surface of the car may need to be loosened with the help of penetrating oil. Allow the oil a couple of hours to figure. A tank fitted through the boot floor may have a sealing gasket between the tank and therefore the floor. If it doesn’t have a gasket, seal the joint with mastic. Bolt within the new tank, then reattach all the connections. Refill with petrol, check for leaks and see that the fuel indicator registers.

Cleaning a blocked breather

A blocked breather within the tank causes the same symptoms as running out of fuel, although the fuel gauge doesn’t indicate ’empty’. Test by quickly removing the filler cap. If there’s a loud sucking noise, the breather is blocked. The tank may breathe through a vent within the cap. this will become blocked or a new, non-vented cap may are fitted by mistake.

Many cars have a second, small-bore hose from the highest of the tank or filler neck, which can loop up and right down to prevent siphoning. make sure it’s not blocked by dirt. A few cars use a broad hose with a closed end. rather than letting in air, it collapses to equalise pressure. this sort is maintenance free.

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