How to Test a Fuel Injector at Home

How to test a fuel injector: the steps

Work with the engine off and keep the area clear of smoking and open flames, with face and eye protection on. A pulse tool fires the injector so you can watch what it does, and an ultrasonic machine cleans it and measures what it delivers. The allsun, AUTOOL and THIKPO listings state petrol vehicles only, not diesel engines. The LUTIFIX listing states no fuel type, so check its listing before using it on a diesel injector.

Start with the pulse check, then move to spray and delivery. For pour-in cleaners, see our best fuel injector cleaner guide.

Pulse the injector and watch the spray

A pulse tool fires the injector so you can watch the spray without the engine running. The allsun kit has 8 pulse modes and 4 pulse signal output modes, short, medium, long and continuous, with a large LED display and a long test lead. The THIKPO kit has 8 pulse modes too, with 4 pulse modes at 12V EFI and 4 pulse modes at 5V GDI, an LCD display, and a 4-wire dual-channel design that pulses 2 fuel injectors at the same time. Each works with any fuel pressure gauge, and the pulse timer may be used with a fuel pressure gauge while the engine is off.

Watch for the faults the listings name: stuck, leaking or burnt-out injectors on the allsun kit, and blockage, leakage, damage and burnout on the THIKPO kit. The AUTOOL machine evaluates atomization quality, leakage and blockages, plus spray pattern angle and shape, under simulated idle, medium-speed and high-speed conditions.

Measure delivery and check for leaks

Spray pattern is only part of the check. The AUTOOL machine measures individual injector fuel delivery volume and uniformity across cylinders, with 4 individual 110ml test cylinders and bright backlighting for checks on up to 4 injectors at once. The LUTIFIX machine uses 100ml glass cylinders and runs 9 functions, including atomization, leakage, clogging, spray pattern and injection balance under various RPM conditions.

Use the adapters that fit: the LUTIFIX kit includes 5 adapter sizes, the THIKPO kit includes 8 adapters with 2 additional specialized adapters for BMW and Audi, and the AUTOOL machine includes multiple adapters compatible with most common 5V and 12V fuel injectors, excluding specific low-voltage direct injection types.

Clean the injector with ultrasound

When the spray is uneven or the delivery is low, cleaning is one possible fix: the AUTOOL listing states carbon deposits cause unstable idling, weak acceleration and difficulty in starting, and that injectors should be cleaned regularly with a fuel injector cleaner machine. The AUTOOL machine has a 1000ml ultrasonic cleaner tank for batch cleaning of multiple injectors, and the LUTIFIX machine has a 2L tank with heated cleaning fluid and recyclable cleaning solution, cleaning up to 4 injectors at once. Pour cleaning fluid only into the ultrasonic cleaning tank on the top of the machine, never into the internal chambers, per the AUTOOL listing. For the check, the AUTOOL listing states that 99% purity alcohol must be used in the designated compartments, and no other liquids such as water, detergents or fuel may be used. The THIKPO kit needs a cleaner that is not included, plus a 12V DC battery power supply that is not included.

Fuel injector gear for the job

Each pick below handles a part of the job: the LUTIFIX machine covers heated ultrasonic cleaning and injector checks, the AUTOOL machine covers ultrasonic cleaning with delivery measurement, the THIKPO kit covers dual-channel pulse checks, and the allsun kit covers individual pulse checks with a 12V battery.

Safety

Never smoke or have open flames near the vehicle, and wear face and eye protection while doing this work. Work with the engine off, and never short the battery positive terminal and negative terminal. The allsun, AUTOOL and THIKPO tools are for petrol vehicles only, not diesel engines, and the LUTIFIX listing states no fuel type, so check its listing first. On the AUTOOL machine, pour cleaning fluid only into the ultrasonic cleaning tank, never into the internal chambers. For the AUTOOL check, use 99% purity alcohol, and do not use other liquids. Never run a fuel engine in a closed garage.

FAQ: garage tools

Can I test a fuel injector at home?

Yes, with a pulse tool and a 12V battery. The allsun kit and the THIKPO kit operate injectors individually to diagnose fuel delivery problems on petrol vehicles with electronic fuel injection, with the engine off.

What does a fuel injector tool check?

A pulse tool checks for stuck, leaking or burnt-out injectors. The AUTOOL machine evaluates atomization, leakage, blockages, spray pattern angle and shape, and delivery volume and uniformity across cylinders.

Can these tools test diesel injectors?

No for the three tools that state it: the allsun, AUTOOL and THIKPO listings state that diesel engines are not supported. The LUTIFIX listing states no fuel type, so check its listing before using it on a diesel injector.

What fluid do I use for the check?

The AUTOOL listing states that 99% purity alcohol must be used in the designated compartments for the check. Cleaning fluid goes only into the ultrasonic cleaning tank on the top of the machine, never into the internal chambers.

How many injectors can I clean at once?

The LUTIFIX machine cleans up to 4 injectors at once in its 2L tank, and the AUTOOL machine checks up to 4 injectors at once in its 4 x 110ml cylinders. The THIKPO kit pulses 2 fuel injectors at the same time, and the allsun kit operates injectors individually.

Do I need a 12V battery?

For the pulse kits, yes. The allsun kit runs on a 12V vehicle battery and needs a full 12 volts, not a 9V battery, per the listing. The THIKPO kit runs on a 12V battery or an external DC 12V power adapter of at least 1.5A. The bench machines run on mains power instead: the AUTOOL on 110V and the LUTIFIX on 110V/220V.

Related: the diagnostics and electrical hub, best fuel injector cleaner and best fuel injector ultrasonic cleaning machine.