Close up of old broken gas injectors of the LPG Liquefied Petroleum Gas alternative fuel system of a car.

Fuel Injectors: What are they and how do you know when you need to replace them?

For the majority of drivers, all they know about their fuel is that they pump it out of the nozzle at the filling station and into that little hatch at the back of their car. From then it might as well be sorcery. Almost all cars on the roads today are powered by fuel injection, helping get the fuel from the tank, via the pump, into the engine and power you along the road. But how exactly do they work, where are they and how do you fix one? Read on to find out more.

But first, if you’re struggling to get your car’s reliability in check and your injector is the latest in a long line of problems, maybe it’s time to cut your losses and send it to the scrapyard once and for all. Scrap Car Comparison is here to make that decision as easy as possible for you, and with certified buyers across the country, we can guarantee you the very best price, no matter what. Not only that, but with all of our buyers being registered Authorised Treatment Facilities, you can be safe in the knowledge your car will be disposed of in line with all government regulations. Get started today and find out just how much your car could be worth as scrap or salvage.

Close up of a man's hands as he replaces a fuel injector

What is a fuel injector? 

A fuel injector, simply put, is an electronically controlled valve found within your car that controls the amount of fuel that can be sprayed into the engine. Pressurised fuel enters the injector from the fuel pump and is fed through a tiny nozzle, the effect of which atomises the fuel – making it a fine mist which allows it to burn much easier. Sensors within the car’s ECU control the amount the injector stays open.

Where is the fuel injector located? 

Fuel injectors are usually found within the intake manifold and often close to each respective cylinder head. Diesel drivers will more than likely find their injector within the cylinder head, while drivers of petrol-powered cars will see their injectors on the intake manifold.

What causes a faulty fuel injector? 

Fuel injectors can go faulty as carbon and other contaminants begin to build up and clog the injector. These clogs can prevent the injector from closing fully, which can result in a drip, causing a misfire. Dry or cracked rubber seals, or even cracks within the pump itself can also cause the injector to begin failing. The electrical elements are liable to standard wear and tear, such as heat, age and moisture damage.

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How to tell if your fuel injectors need to be replaced 

You will likely go through your entire driving career without ever having to replace a fuel injector, such is their longevity. Instead, it’s more likely that you’re going to need to get it cleaned, or at least have it looked at by your local garage or mechanic. Tell-tale signs that you’re nearing this point include:

  • Engine misfire – issues with the injector mean that the delicate balance of fuel and air being syphoned into the engine is not as it should be, which can cause a ‘splutter’ effect as you’re driving.
  • Rough idling – Similar to a misfire while driving along, spluttering when the car is idle is the result of a constantly changing RPM even if your feet are off the pedals. This is often accompanied by stalling.
  • Reduction in fuel mileage – Quite an obvious one, given your expected mileage is based on your injectors working exactly how they should; any drop in your miles to the gallon could point towards the need to get your injectors looked at.
  • Erratic tachometer – This one is likely to go hand-in-hand with rough idling, and you’ll notice that the juddery nature will probably match up with the needle pulsing up and down the rev gauge.
  • Car fails to start – If your injectors aren’t doing their job properly, then the right amount of fuel and air won’t be provided to your engine’s internals. As a result, there may be a distinct lack of combustion for your internal combustion engine. This is a rare case, and could be a sign of something else, but by this point you’re probably going to be getting your car to the nearest garage anyway.

How long do fuel injectors last and how often should they be replaced? 

Most fuel injectors should have an adequate life expectancy to last your car’s entire life, with some of the major manufacturers claiming that their injectors can last 1 billion cycles and in ideal conditions will never need replacing. Of course, you won’t be driving in ideal conditions every day and, as with most car parts, the longevity of injectors is often measured in mileage. That can be anywhere between 50,000 and 100,000 miles – which is why you’re highly unlikely to ever encounter a situation where you’ll need new ones.

Are fuel injectors universal? 

Absolutely not – there may be some aftermarket options out there that claim to be a ‘one size fits all’ solution, but nothing will ever fit your car quite in the way that OEM parts made for your car will. Fuel injectors made for a wide range of cars will not perform to the best of their ability as they’ll need to make compromises in order to fit across the board and if there’s a part that you don’t want to be compromised in any way, it’s a fuel injector. We’ve already discussed what slight leaks can do to your injector, and an injector without a perfect fit could perform in the same way as one that’s leaking.

Young mechanic wiping his hands while repairing car engine in auto repair shop.

Can a faulty fuel injector cause a misfire? 

One of the common symptoms of a faulty fuel injector is a misfire, because as an injector begins to falter, the delicate mixture of fuel and air it distributes will no longer be as required, which can wreak havoc with your engine as it trundles along.

Can you drive with a bad fuel injector? 

Driving with a faulty fuel injector isn’t something you’ll find many motoring experts recommend, as you run the risk of more problems as a result. We’ve already mentioned the issues of misfires or rough idling, but you could also find that the injector problems cause you to stall or even flood the engine. In this case you’re likely to be put in a much more dangerous position if you’re stranded, so it may be better to not take the risk at all and get it fixed before you undertake any major drives.

How do you test fuel injectors? 

Testing fuel injectors isn’t the most complex of jobs for someone who knows what they’re looking at when you pop the bonnet open, but if something like topping up oil or checking tyre pressures is the most advanced work you’ve done on your car, maybe leave this to a professional.

There are a number of tests that you’ll want to carry out to ensure that the injectors are working correctly. 

  • The easiest way – The simplest test is to use a long metal rod – even something as primitive as a screwdriver. Simply place one end against the injector, and listen to the other end. If you can hear clicking, then that will confirm that it is working.
  • The Circuit Power test – Switch the key into the on position and place a test light or voltmeter on the negative side of your car’s battery. Probe both sides of the injector wiring connector and if neither illuminates, you’ll need to test the fuse. If the fuse is fine, then there’s likely a connection issue somewhere.
  • The Visual test – You may be surprised to know that you can visually check the functionality of your fuel injector. Simply remove the cover of the air cleaner housing (your air filter will be here), and get someone to start the engine. You should be able to see the fuel coming out of the injector in an inverted V pattern. If it is a single, solid spray or has no discernible pattern, then there’s something amiss.

Can faulty fuel injectors cause an MOT failure?

If your fuel injector has a leak in any way, then your car will not pass its MOT. A fuel leak of any type at any point of the system will result in an instant MOT failure.

Get the best price with Scrap Car Comparison

If your car’s injectors have been playing up and are giving you a very uncomfortable ride, you might find it easier to simply get rid of the car as a whole instead of trying to fix a potentially never-ending list of headaches. By using Scrap Car Comparison you can guarantee yourself the very best price in a stress-free manner, and with collection agents working across 99% of the country, you’re never too far from our service, either. Get started today, and by just providing us with your postcode and registration number you can find out just how much your car may be worth as scrap or salvage.

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