Rubber connectors are often damaged by being removed in the wrong way. If they are pulled straight off, the tension makes them become narrower and tighter, and they may tear.
They should be twisted off. This also applies to longer lengths of rubber hose.
Pushing on a connector or hose is seldom a problem, but do not use a lubricant to ease it or jointing compound to seal it. This applies to all types of connector used on fuel pipes.
Make sure any clips are correctly positioned. Do not overtighten them, particularly when they are wire clips, for these can cut through a hose.
When a metal connector needs replacing, the pipe is generally damaged as well as the connector. If there is enough pipe, you can cut off the damaged section.
With the type of connector that relies on an expanded or ‘belled’ end on the pipe, you must bell the end before screwing up the nut tightening the nut completes the belling and forms the seal.
Strictly this should be done with a special belling tool, but in an emergency you can usually manage it by sticking a pair of long-nosed pliers into the end and twisting them round to expand the end into a bell shape.
If you are using a new nut, slide it over the end of the pipe before you start to bell the end, or it will not go on. Have the joint sealed with a proper belling tool as soon as possible.
With an olive joint, always replace the olive when you reconnect the joint, whether or not you have replaced any other parts.
Avoid overtightening connectors, which can cause them to leak.
Where plastic pipe is joined with nut-type joints, make sure it does not get twisted when you are loosening or tightening them. This is a particular danger with joints which have a nut at each end. Use two spanners.
The section of fuel line in the engine bay is less exposed to damage than the piping under the car. But heat and oil can damage its rubber connectors.
Special clear-plastic tubing, which is both flexible and oil and fuel resistant, is often used here, particularly where an original rubber hose has been replaced.
Some plastic can become hard and awkward to flex – always use the grade recommended by the spares department of a dealer for your make of car, though it may cost more. Once a plastic fuel pipe has hardened with age, replace it.
Apart from leaking, fuel lines can also become blocked. A total blockage will stop the car, but a partial one may only cause fuel starvation at high speed, which is hard to diagnose as there may be other causes. One clue is that the effect is often spasmodic.
If you suspect a blockage, the quickest way to check is to free both ends of the pipe and blow through it. Use your mouth, not a high-pressure air line, which may cause damage.
An air line may also loosen dirt, which later falls back and blocks the pipe again.
Do not blow into the fuel filler hole it will not reveal a blockage and could be dangerous if the tank is full. You might inhale petrol – or fumes – and get it in your eyes.
If you find a blockage, it may be at a filter. Some filters mounted in the fuel line look just like rubber connectors. There is also one on the fuel pump (See Cleaning fuel-pump filters).
Kinks and dents in the line itself can cause a blockage.
Old rubber hose – especially the braided type – can collapse internally without this being evident on the outside.
Check by blowing, not by poking anything through the hose which may damage it.
Repeated blockages may be caused by dirt or rust in the fuel tank. If so, the tank must be removed, cleaned and flushed out, or replaced.
When working on the fuel system, do not wipe the ends of pipes with soft rags. Small threads or bits of fluff can come off and block a pipe.
Occasionally a slack joint in the fuel-pipe system allows air into the fuel. This, too, can cause fuel starvation at high speed.
The trouble is difficult to spot. A fuel-pump filter with a glass bowl may show an air leak by a stream of bubbles. Routine checking of all joints for tightness should prevent or cure the problem.
Another cause of fuel starvation can be a blockage of the tank ventilation. This may even stop the engine.
The trouble will show when air hisses in as the filler cap is released. The normal type of tank vent is a plastic pipe leading from the top of the tank to below the car.
If this cannot be reached to unblock it, disconnect the pipe at the fuel tank, and blow through it with a foot pump.
Belling the pipe in an emergency