Car Won’t Start After Replacing Fuel Injectors

So, you have replaced the fuel injectors of your car and your car won’t start after replacing fuel injectors? Well, I got you as I also faced the same problem in my vehicle.  

In this guide, I am going to tell you how you can solve this problem and start your car again. Now, first of all, before going to the solution, let me tell you a little bit about how to fix this problem and start your car again. You need to know that when you replace the fuel injectors of your car, you may face such kinds of problems and issues, but it depends on the reason for which it is going to happen.

Sometimes, it can happen due to the reasons like a problem with the fuel pump, fuel line, fuel filter, throttle body or the problem may occur due to the fact that you haven’t checked the car properly before going to change the fuel injectors. In other cases, there can be a problem with the injectors themselves. It can also be due to the poor quality of the fuel.

It can also be due to a damaged car battery. In other cases, you may face a problem because of the issue with the wiring of your vehicle. In any case, it is always better to keep checking your car carefully before going to replace the fuel injectors.

Also, check my guide on car won’t start after replacing the crankshaft sensor.

Why Car Won’t Start After Replacing Fuel Injectors?

There are different causes due to which car won’t start after replacing the fuel injector. Some of the reasons for the car not starting after replacing the fuel injector include a bad fuel injector, bad electrical connection to the spark plug coil, improper installation of the fuel injector, the loose connector of the fuel injector, leaking fuel injector O-ring, and bad spark plugs.

Bonus Read: Car won’t start after changing oil

Can Fuel Injectors Cause Car Not Start?

Yes, fuel injectors can cause cars not to start if they fail to deliver the desired fuel. A fuel injector is an electronically controlled valve responsible for delivering a precise amount of fuel into the engine. This is done by pushing the fuel under pressure through the nozzle, into the engine’s intake manifold, or directly into the engine cylinder. If the injector fails to work, you may experience a rough idle, hesitation when accelerating or even a total engine starting failure.

In some cases, the problem may be caused by the fuel pump. When this happens, the fuel pump may not be pumping fuel into the engine. The fuel pump is responsible for pumping fuel out of the fuel tank and into the engine. 

If the fuel pump is faulty, it may not be pumping fuel out of the tank. This could happen when the fuel line or the fuel filter is clogged. The fuel filter is located at the bottom of the fuel tank. If the filter is clogged, it will not allow fuel to flow out of the tank.

Causes Of Car Won’t Start After Replacing Fuel Injector

1. Faulty Fuel Injector

The most common reason for the car not starting after replacing the fuel injector is that the new fuel injectors are bad. Some engines work with only OEM fuel injectors as they are designed to handle a certain pressure of fuel. 

If an aftermarket fuel injector can’t install a high fuel pressure, the fuel injector will be stuck open and flood the cylinder with fuel. For combustion, a certain air/fuel mixture is required. If too much fuel drops into the cylinder, the air/fuel will become rich. Thus, the car won’t start.

On the other hand, the solenoid in aftermarket fuel injectors can also fail to operate, due to which the fuel is not injected into the cylinder and the car won’t start. Fuel injectors simply have coils serving as magnetic carrying electric current. A fuel injector contains three components: a pin, a coil, and a spring. The spring keeps the pin closed until a current is applied to the coil, which opens the pin and allows fuel to flow through it.

fuel injector construction

There are several methods to test a bad fuel injector. You have to check the fuel injector electrically, and also make sure it is delivering the fuel. First, you should have a multimeter and connect its probes to the terminals of the fuel injector.

Set your digital multimeter to an appropriate value on the Ohms scale according to the resistance specifications for your particular fuel injector (usually, you need to set the multimeter to read at least up to 30 Ohms).

If the resistance across terminals of the injector reads infinite resistance, it means the coil in the injector is opened. If the multimeter shows OL or very small resistance, it means that the coil in your injector has short-circuited. If it shows resistance specified in the specs of your fuel injector, it means that the coil of fuel injector is fine.

testing of fuel injector with multimeter

Another test for a bad fuel injector is to observe if it is emitting a clicking noise or not. For this, you would need a long screwdriver. Now, pull out the fuel rail. But make sure that it is connected to the fuel supply hose. Turn the key on to prime the fuel pump and pressurize the fuel line. Now, hook the 9v or 12v battery one by one to each fuel injector and try to hear its ticking noise with a long screwdriver.

That ticking noise is basically the opening and closing of a pin in the fuel injector. Also, see if the fuel injector is injecting fuel in a certain direction without leaking or not. If it’s leaking, you would need a new fuel injector.

You can check out the following video from 2:40 to get an idea of how to test fuel injectors.

Apart from that experiment, check these things on the fuel injector:

  • Look for burrs on the injector inlet
  • Check nozzle holes for hole erosion or plugging
  • Inspect the end of the nozzle for burrs or rough machine marks
  • Look for cracks at the nozzle end

2. Fuel Injector Is Not Properly Installed

Another reason the car won’t start after replacing the fuel injector is that the fuel injector is not properly installed. While installing, the O-rings of the fuel injectors can get pinched if you do not properly lubricate the O-rings with clean motor oil.

If the O-rings of the fuel injector were not lubricated before putting on the fuel injector, they would get pinched and the seal would break, resulting in flooding the engine compartment with fuel. If the fuel injectors come with the O-rings on, lubricate the O-rings with motor oil while the O-ring is in place.

Moreover, make sure that O-rings are installed on the bottom and top of the fuel injector and that they are new and compatible with the engine and fuel injector. The old O-Rings will have micro-tears or will be hardened, not making a great seal. Usually, the engine manufacturer has specified the part number of the O-ring to be installed on the fuel injector. Use your palm to push the o-rings until they sort of “pop” into place.

Put the fuel injector back into the engine by pushing its nozzle first into the hole. Rock it slightly. You’ll feel a slight “pop” as it seats.

Moreover, when you remove the fuel rail, make sure that any dirt or debris does not get into the hole where fuel injectors are plugged in. It will also cause the car not to start.

After installing the fuel injector, turn the ignition key to the “start” position a few times (with several seconds in place). You’ll hear the fuel pump prime the fuel lines.

3. Check Electrical Connections To Fuel Injector

While removing the fuel rail to replace the fuel injector, the electrical connection can break at some point if the insulation of the wire rubs against the metal during the installation and removal process. First, you have to see if there is corrosion on the all connectors of the fuel injectors.

First, you should check if the wiring harness of fuel injectors has shorted to the ground. For this, connect the red probe of the multimeter to the one terminal of the connector and the black probe with the negative terminal of the battery. Similarly, repeat the step for another terminal of the connector. If there is a short circuit, the multimeter will show negligible resistance.

Next, check if there is any voltage across the terminals of the connector. If the connector is good, it should read voltage around 12V.

4. Spark Plugs Are Drenched With Fuel

Sometimes, after replacing the fuel injector, the spark plug gets fouled with the fuel. If you spray starter fluid in the intake close to the throttle body and see if the car cranks or not. If it doesn’t, it means that there is a problem with the fuel ignition system.

Spark plugs are fouled with fuel if the fuel injector is leaking. This happens if the fuel injector is stuck open or the O-rings of the fuel injector are damaged. This happens when the fuel injector is not spraying fuel with atomization and is simply dripping the fuel. In such cases, you will have to remove each spark plug and check if it’s dry or wet with the fuel. To remove the spark plug, you can read this guide.

You can watch this video from 4:00 to test the spark plug:

Also, take out the oil and check if you smell pure gasoline in it. If it smells, you also need to change the oil.

5. Throttle Body Is Disconnected

Usually, a throttle body has to be removed to replace the fuel injectors. Now, if you have not correctly connected the throttle body and MAF (Mass Airflow Sensor), the engine control module will not detect any incoming air. Since the fuel is injected based on the flow of air. So, if the engine control module does not measure any volume of air, the fuel will not be injected and the car won’t start.

Moreover, if you have cleaned the air intake while replacing the fuel injector, some of the junk might fall into the combustion chamber that is keeping your car from getting started.

6. Camshaft Sensor Is Disconnected

A camshaft sensor also comes into the way while replacing the fuel injector. The camshaft sensor compares camshaft speed with the crankshaft speed and sends signals to the engine control module for ignition timing. If the camshaft sensor has disconnected, it will also cause the car not to start.

Should I Reset ECU After Changing Injectors?

It ios not necessary to reset or reprogram the ECU after installing new fuel injectors as fuel injectors directly affect the fuel delivery of the vehicle. They are not sending any signal to the ECU like the sensors. So, you don’t have to reset the ECU. However, if there are any error codes stored in the engine’s memory, you will have to reset the ECU after installing the new fuel injectors.

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