How To Test Fuel Injectors | Autance

What Is a Fuel Injector Before we start to look at how you might test fuel injectors, it is probably…

  • 259
How To Test Fuel Injectors | Autance © How To Test Fuel Injectors | Autance

What Is a Fuel Injector

Before we start to look at how you might test fuel injectors, it is probably a good idea to clarify exactly what a fuel injector is.

A fuel injector is the modern-day equivalent, (or rather, replacement), for the carburettor – that often-temperamental piece of engine compartment equipment that mixed fuel with air in order to produce a combustible mixture suitable for powering the vehicle’s engine.

Although carburettors still exist, mainly on classic cars and specialist vehicles, they have been replaced on almost all new production vehicles since the mid-1990s, by fuel injection systems working in conjunction with the vehicle’s ECU (Engine Control Unit).

This is both a good thing, and a bad thing. For most motorists, repairing or even adjusting, a fuel injection system is close to impossible without a considerable investment in tools and equipment. The carburettor, on the other hand, provided endless fun for the keen amateur whilst trying to improve performance or deal with a glitch.

However, we are where we are, and the chances are that your vehicle will be fitted with some kind of fuel injector. Although fuel injectors are more reliable than carburettors, generally speaking, they can still go wrong and will usually involve a trip to the service garage in order to resolve the problem.

So, is it possible to diagnose fuel injection problems yourself and, if so how and with what equipment?

How To Identify a Possible Problem With Your Vehicle’s Fuel Injector(s) – What Are The Likely Symptoms?

There are several symptoms which may indicate a problem with the fuel injection system of your vehicle but to get us started, the main ones (i.e. most frequently occurring), to be aware of are as follows:

  • Your vehicle’s engine idles roughly or unevenly and/or it can often be prone to stalling frequently without any apparent reason.
  • The engine vibrates whilst idling or when in normal use, often noisily making the ride quite uncomfortable.
  • The engine is prone to frequently misfiring.
  • The “Check Engine” warning light on the dashboard comes on.
  • There is a fuel leak – look out for the characteristic smell of leaked fuel, especially in or around the engine compartment.
  • The engine has power surges whilst running and runs inconsistently, sometimes with a feeling of “hesitation” or “lulls” in power.
  • The vehicle’s fuel economy can be seen to gradually deteriorate over time with visits to the fuel pumps becoming ever more frequent.

Of course, most, if not all, of the above symptoms can have more than one probable cause – they are not necessarily indicative of a faulty fuel injection system, with faulty or dirty spark plugs being a common cause of many of them – but it is a useful checklist to begin the process with.

If You Can, Get The Code – The OBD (On Board Diagnostic) Code That Is.

Since the mid 1990’s almost all new vehicles are fitted with a computerised engine management system which, in addition to controlling the vehicle’s engine and other functions, also reports on any problems that may occur.

A universal system of codes is used to point to potential problems and the specific codes that could point to a fuel injector fault are in the range P0000 to P0299 (air/fuel mixture control) but are likely to be somewhere between P0300 – P0308 where the last digit, e.g. 8, denotes the cylinder in which the fault has occurred so a code of P0308 would be in cylinder number 8.

You can get this information by taking your vehicle to a service garage, there would of course be a charge, or you could invest in an OBD scanner or code reader which, for the amateur mechanic or enthusiast, would be a value for money and very useful investment.

As Always, Prevention is Often Better, (and cheaper), Than The Cure.

It is also worth saying that, as with many vehicle maintenance issues, prevention is almost always better, (and cheaper), than the cure. One of the easiest, low cost and effective ways to prevent and avoid fuel injection problems is to keep the system clean. If the very thought of cleaning any part of an internal combustion engine fills you with dread, fear not! It is quite possible to keep your fuel injection system clean and performing at peak efficiency simply by making use of a fuel injector cleaner.

A proprietary fuel injector cleaning fluid can be used at regular intervals and will not only clean a fuel injector system that has become clogged up with use but will also prevent dirt from accumulating in the future and avoid similar problems happening again.

Fuel injector cleaning fluid is a fuel additive, easy to use, very good for preventive maintenance and it is a relatively low-cost solution – especially when compared to having your vehicle repaired in a service garage.

It is worth bearing in mind that, if things get really bad, the cost of replacing a damaged fuel injector can run into thousands depending on the size and type of vehicle you have, so a little bit of preventative maintenance is well worth while.

Some mechanics recommend using a shot of cleaning fluid additive every time you fill up with fuel but that may not always be necessary. However, if you have noticed any of the above symptoms, even if the signs are only slight, it may well be worth using a cleaning fluid regularly in order to prevent the problem from escalating. A good guide, which many people use, is to clean your fuel injectors with a fuel additive every time you change your oil.

If your problem is more severe then you may have to consider using the services of a professional fuel injector cleaning service which, although much cheaper than having to replace the fuel injector unit, could still come with a price tag upwards of $100.

If it becomes necessary to replace fuel injectors it is standard practice to replace them all, not just the faulty one, to maintain an even performance – another incentive to keep your system clean and to have it checked regularly.

Do You Have a Problem? – How To Check Fuel Injectors

If you want to avoid the cost and inconvenience of having to take your vehicle to a service garage to have its fuel injectors tested, and maybe repaired, then you may like to learn how to tell for yourself whether there is likely to be a problem first – after all, a service engineer may well charge a hefty fee simply for telling you that you have a potentially expensive problem with your fuel injectors.

It is possible to test fuel injectors yourself, at least up to a point, without the need to buy expensive equipment or having to undergo extensive training. Look out for any obvious signs of a possible problem on your dashboard – if the engine check light comes on then that could point to any number of possible faults and a faulty fuel injector is certainly one of them.

One of the most popular ways to check fuel injectors is to listen – your ears can tell you a lot, if you know how to listen to your fuel injectors and you understand what they are telling you when you do.

In an ideal world, in order to do this properly, you’d have a stethoscope – just like the one your doctor uses, but we know that it is unlikely that you will have one of those, unless you are a doctor, nurse, or other healthcare professional of course.

Assuming that you do not have access to a stethoscope, here’s how you can listen to your fuel injectors using a piece of equipment nearly everyone will have, or which can be purchased for a small price – a large screwdriver! The bigger the better, with a long stem if possible.

Yes, the common or garden screwdriver can be your best friend here, just follow this simple checklist and identify problems with your fuel injectors:

  1. Turn on the engine and let it idle
  2. Take the largest and longest screwdriver that you can get your hands on and place the tip at the base of the fuel injector.
  3. Make sure that you, your hair and your clothing is well clear of any moving parts
  4. Put your ear to the handle of the screwdriver and listen carefully.
  5. If all is well with the fuel injector being listened to, you would hear a continuous clicking noise. This indicates a smooth-running injector. If the clicking is intermittent then there is likely to be a problem with that injector. If there is no clicking at all then that injector is faulty and will require cleaning or replacing.

Depending on how many cylinders your engine has, just repeat the above procedure for the injector on each cylinder. Simple but effective – and free of charge.

Anyone who remembers the days of manually adjusted carburettors will appreciate the convenience and reliability of a fuel injected engine although many still hanker after having the ability to tinker and tune their engines manually. For most of us, however, we have other things to do and the combination of fuel injection and the Engine Control Unit is almost universally appreciated.


  1. How to Test a Fuel Injector – Do It Your Self
  2. How to Test Fuel Injectors – WikiHow
Commnets 0
Leave A Comment