How to check fuel injectors

The question of how to check the injectors may be relevant for gasoline and diesel cars. The ways and methods of testing will be different, but feasible for any car owner at home.

All you need is a test light bulb with wires and a multimeter.

What are the Symptoms of Bad Fuel Injectors

The main malfunction that can occur with an injector is clogging or complete failure of the injector. Signs of malfunctioning injectors include the following:

unstable engine operation at idle;
significant increase in fuel consumption;
problems with engine start, especially when cold;

Example of clogged injectors

in some cases there can be a significant amount of black smoke from the exhaust pipe (in case a lot of fuel gets into the combustion chamber through the leaking injector), and sometimes it is also accompanied by periodic loud popping from the muffler;
the loss of dynamic qualities of the car, is expressed in the fact that the car accelerates poorly, it lacks power, you can feel a jerk while driving even on a level surface, including when resetting the gas and when changing the value of the load on the engine.

These signs can of course point to other problems with the power unit of the car, but if they occur, we still advise you to check the injectors and, if necessary, to clean or replace them. Also notice that in some cases, “check engine” sensor icon may glow on the dashboard, so it is worth checking OBD2 error codes. Such DTCs as: p0300 — p0306 or p0200 — p0206 can indicate faulty injectors or problems with their wiring. If you find faults related to the injectors, you can swap injectors and if the code goes to another cylinder, then the problem is definitely in the injector.

Injector malfunctions cause considerable wear and tear on the internal combustion engine.

What malfunctions can appear?

Among the main malfunctions of the electromagnetic injector can be:

No signal from the ECU (this often occurs due to a break in the wiring to the injector);
malfunction or complete failure of the winding;
clogging of injector outlet.

Practice shows that the last option is the most frequent reason of complete or partial injector failure.

How to Test Fuel Injectors

Checking the power supply to the injector

There are several methods on how to test automobile fuel injectors. Let's list them in order with a detailed algorithm of actions.

The first step is to find out which injector in the ramp is not working, you can use the above method that involves interchanging the injectors or you need to listen with a stethoscope. Instead of it you can use a thin metal rod (you can also use long screwdriver) and turned on the microphone on the phone (touch the rod to the injector and to the microphone). If you do not hear clicks of the injector work when the engine is running, then either it is constantly pouring, or it does not work at all, or the ECU turned it off (the ECU can turn off the injector work when detecting cylinder failures).

If it does not click or sounds uneven and there are other vibrations and knocks, it means that the injector in question is clogged or not triggering.

Start the test by unscrewing the spark plugs, as you can tell from their condition whether fuel is getting into the cylinder.

The second stage of the check, to understand whether the power and pulse are supplied to the injector. To do this, you will need a checker (there is a special device, but you can take a light bulb and two wires).

How to Diagnose, Test and Clean Dirty, Clogged or Bad Fuel Injectors: video

Remove the connector from the injector.
Switch on the ignition, but do not start the engine.
We fix the minus end of the tester with the bulb to «mass» (free area on the engine, body or on the minus terminal of the battery), and touch the contacts in the connector with the second end one by one.
When touching one end the light bulb should be on all the time.
Start the engine and touch the second terminal in the connector (pulse «minus»). If there is no wiring damage or short circuit, the tester lamp should blink.

If there is no power or signal minus leave the tester connected, bend the harness with injector wires, the damage will show itself by blinking the light bulb. When looking for the place of breakage pay attention to the place where the wires are fastened and the bends.

The third step is to check the resistance of the injector, and the fourth step is to check its visual operation of the fuel atomization.

Check Fuel Injectors With a Multimeter

You can check the injectors without removing them with a multimeter. First, find out which injectors are installed on your car — high or low impedance (electrical resistance). This data will be necessary to perform an accurate diagnosis. If you don't know what resistance the injectors on your car have, you can check all of them one by one, so you can at least know if all of them have the same resistance. To check the injector with a multimeter, you need to stick to this plan:

How to Check Fuel Injector Resistance with a Multimeter: video

Turn off the ignition and remove the «minus» terminal from the battery;
remove the injector connectors;
set the multimeter in the mode of measuring the insulation resistance (ohmmeter) in the range from 0 to 200 ohms;
connect the tester probes to the injector terminals and measure.

High impedance injectors have an insulation resistance of 11 to 17 ohms and low impedance injectors have an insulation resistance of 2 to 5 ohms.

If the measured insulation resistance value differs significantly from the specified value, it indicates that the injector is defective. Accordingly, the injector should be dismantled and a detailed diagnosis should be performed.

Remember that when testing injectors with a multimeter, you need to diagnose all devices one by one! This way you can check which injector does not work.

It is important to know that voltage to injectors from ECU is pulsed, not constant. Therefore, it is recommended not only to measure resistance with an ohmmeter but also to take an oscillogram of pulse voltage transmission with an oscilloscope, so you can see what peak voltage it takes. The tester will only show you average values.

How do I check the starter injector?

If you have an older model VW, Audi, Skoda, Seat, and others with a mono injector there will be an one starting injector in front of the throttle. To check it, you need to:

check in pairs the contacts from the injectors and compare them with the data from the manual (as a rule, these values should be within 1.2...1.6 ohms);
when checking contacts 1 and 4 make sure that the intake air temperature sensor is working properly, for this also use the resistance data from the manual;
if the resistance values are out of tolerance limits, it is necessary to diagnose the injector in more detail.

If the multimeter shows that the injector is working it is necessary to check its performance (amount of atomized fuel, stability, spray pattern).

How to Test for a Clogged Fuel Injector

In the case of a clogged injector, it may leak fuel or atomize badly. Therefore first you need to check the jet, and secondly, you need to compare the performance. It is necessary to dismantle the whole ramp or separate injectors. In the service, clogging and performance are checked on a special stand. At home you can check if the injectors are spraying and what is the spray pattern this way:

Example of operation of injectors on the bench: click to enlarge

unscrew and lift the fuel ramp;
lay a dense cloth on the place where injectors are installed;
ask a helper to try to start the engine for 3 to 5 seconds;
observe if and how injectors are spraying fuel (flare should be equal and even on all injectors).

If all injectors work but have different spray patterns, try to clean them. Cleaning can very often save you money on replacing them, as one can cost over $100.

Dave Wagner 19 May 2022

Repair of running gear, replacement of units, dense repair of auto air conditioning systems.